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Convex parabolic mirrors | Geometric optics | Physics | Khan Academy

Video vocabulary

remember

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US / rɪ'membə(r) /

UK / rɪˈmɛmbɚ /

A1
  • verb
  • To give someone a gift, e.g. birthday, wedding
  • To hold a thought in your mind to not forget it
  • To bring a previous image or idea to your mind

focus

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US / 'fəʊkəs /

UK / ˈfokəs /

A2
  • noun
  • Main purpose or center of interest or activity
  • verb
  • To see clearly by adjusting your eyes or a camera
  • To keep your attention, concentration on one thing

draw

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US / drɔ: /

UK / drɔ /

A1
  • noun
  • Something that attracts people to visit a place
  • A lottery or prize
  • Result of a game, contest where the score is equal
  • verb
  • To attract attention to someone or something
  • To get closer to or approach something or someone
  • To influence a person's involvement in something
  • To move an object by pulling
  • To create an image using pen or pencil and paper
  • To take one thing out of a container, etc.
  • (Of 2 teams) to finish a game with the same score

incident

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US / ˈɪnsɪdənt /

UK / ˈɪnsɪdənt /

A2
  • noun
  • Event, usually unusual or important; accident

jut

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US / dʒʌt /

UK / dʒʌt /

C1
  • verb
  • To stick out or up beyond a surface

part

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US / pɑ:t /

UK / pɑ:rt /

A1
  • adjecitve
  • To some degree; half; not fully
  • noun
  • Division of a book
  • Ratio of something, e.g. 3 of gin, 1 of tonic
  • A line in a person's hair, made with a comb
  • Character an actor plays on stage, movie, or TV
  • Some, but not all of a specific thing
  • Role in causing something to happen
  • verb
  • To make a line in a person's hair, by using a comb
  • To move two things apart creating a space
  • To leave someone, or to break off a relationship

store

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US / stɔ:(r) /

UK / stɔr, stor /

A2
  • noun
  • Place where things are kept for future use
  • Place where you can go to buy things
  • verb
  • To put things in a place for later use

exercise

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US / 'eksəsaɪz /

UK / ˈɛksɚˌsaɪz /

A2
  • noun
  • Physical activity to increase health and strength
  • Set of questions in a text book
  • verb
  • To work out to become stronger and healthier
  • To retain your ability or practice your skills

through

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US / θru: /

UK / θru /

A2
  • adjecitve
  • having finished using or doing something
  • adverb
  • From the beginning of something until the end
  • preposition
  • Over, in, across an entire thing or place
  • Allowing you to pass between, or to
  • By a particular way or process; by the use of

well

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US / wel /

UK / wɛl /

A1
  • adjecitve
  • Being in a fortunate, good condition or state
  • Healthy and in good condition
  • adverb
  • In an acceptable, proper, or successful manner
  • In a complete, total, or full manner
  • A great and considerable degree
  • In a successful way, in a good or satisfactory way
  • exclamation
  • Used to begin or continue a particular statement
  • Used to show you want to start saying something
  • Used to express that you are waiting for a reply
  • You say this to change the topic of a conversation
  • Used to indicate you are making a final remark
  • noun
  • Long deep hole in the ground to get water
  • verb
  • To cause your eyes to fill with tears

head

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US / hed /

UK / hɛd /

A1
  • noun
  • Counter for the number of cattle
  • Natural mental ability or intelligence
  • Leader or person with the greatest authority
  • Mind; mental ability; mental state
  • Side of a coin with a head on it
  • Top part of your body with eyes and a mouth
  • Starting point of something, e.g. a river
  • verb
  • To hit a ball with your head in a game
  • To be first or at the front or top (e.g. a list)
  • To travel or move toward a particular place; To go in a particular direction
  • To become the leader of something
  • To lead or be responsible for something

ray

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US / reɪ /

UK / re /

B1
  • noun
  • Person's name
  • Lines of light coming from an object
  • Fish with a pointed tail and flat body

field

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US / fi:ld /

UK / fild /

A1
  • noun
  • Area of study, such as physics or biology
  • Piece of land used to grow crops/raise animals
  • Open area of land, especially without buildings
  • Grassed area where you play some sports
  • verb
  • To respond to something or answer a question
  • To catch or stop a ball during a game

why

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US / waɪ /

UK / hwaɪ, waɪ /

A1
  • adverb
  • Question word to ask for a reason
  • exclamation
  • (Used to express surprise or approval)

just

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US / dʒʌst /

UK / dʒʌst /

A1
  • adjecitve
  • Proper or appropriate; as is deserved
  • Doing or being what is right or fair
  • Legally correct; having enough evidence
  • adverb
  • Almost; nearly
  • Exactly at the time of
  • Exactly (the same as, like)

stuff

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US / stʌf /

UK / stʌf /

A1
  • noun
  • Generic description for things, materials, objects
  • verb
  • To push material inside something, with force

line

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US / laɪn /

UK / laɪn /

A1
  • noun
  • Border that divides two places or regions
  • Long crease in the skin, often from age
  • Mark that is long, straight and very thin
  • Row of words, letters or numbers that are written
  • Telephone connection
  • People waiting one behind the other; queue
  • Long thin wire, e.g. for electrical signal
  • verb
  • To put material along the inside of something

never

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US / 'nevə(r) /

UK / ˈnɛvɚ /

A1
  • adverb
  • Not ever; not at any time

light

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US / laɪt /

UK / laɪt /

A1
  • adjecitve
  • Being bright making it easy to see; not dark
  • Being pale and lacking darkness of color
  • Not heavy; weighing only a little
  • adverb
  • Carrying few bags when traveling
  • noun
  • A source of energy that makes a room or area bright
  • Way in which something or someone is understood
  • verb
  • To cause something to burn; put a burning match to
  • To provide a way to see ahead

object

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US / 'ɒbdʒɪkt /

UK / ˈɑbdʒɪkt /

A2
  • noun
  • Something you can see or touch, but is not alive
  • Goal or purpose of a particular plan or activity
  • The thing that the action of a verb acts upon
  • verb
  • To disagree; to protest against an idea or plan

anyway

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US / ˈeniweɪ /

UK / ˈɛniˌwe /

A1
  • adverb
  • A word used to change the topic of a conversation

source

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US / sɔ:s /

UK / sɔrs, sors /

A2
  • adjecitve
  • Produces or provides what is wanted or needed
  • noun
  • Piece of information; a person giving information
  • Place from which something necessary comes
  • verb
  • To get, e.g. a raw material, from somewhere

time

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US / taɪm /

UK / taɪm /

A1
  • noun
  • Speed at which music is played; tempo
  • Point as shown on a clock, e.g. 3 p.m
  • Number of hours, minutes needed to do something
  • Occasion when something happens
  • Period or occasion that something occurred
  • Period in history or the past
  • Something measured in minutes, hours, days, etc.
  • How long an event takes; duration
  • verb
  • To check speed at which music is performed
  • To choose a specific moment to do something
  • To measure how long an event takes, e.g. a race
  • To schedule something to occur at a specific moment

one

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US / wʌn /

UK / wʌn /

A1
  • pronoun
  • You; we; people in general; someone
  • The thing or person previously referred to
  • adjecitve
  • Used to refer to people generally
  • Being a strong example of (something mentioned)
  • number
  • Number 1

emit

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US / ɪ'mɪt /

UK / ɪˈmɪt /

B1
  • verb
  • To release or send out (a gas, etc.)

ones

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US / wʌnz /

UK / wʌnz /

A1
  • number
  • Number 1, a single person or thing

might

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US / maɪt /

UK / maɪt /

A1
  • other
  • Used to politely request an action
  • Used to express that something could happen
  • Power, strength, force or influence

cave

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US / keɪv /

UK / kev /

A2
  • noun
  • Large hole in the side of a cliff or hill
  • verb
  • To give in to pressure

map

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US / mæp /

UK / mæp /

A1
  • noun
  • Diagram showing the geography of an area
  • verb
  • To draw a diagram to show the geography of an area
  • To find points of similarity between things

the

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US / ðə /

UK / ðə /

A1
  • article
  • Used to refer to something already mentioned
  • Used to show there is only one of something
  • determiner
  • Used to describe all of a family

image

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US / 'ɪmɪdʒ /

UK / ˈɪmɪdʒ /

A2
  • noun
  • Picture, sculpture or painting of something
  • General idea or opinion of something
  • verb
  • To obtain pictures by scanning them with a machine

surface

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US / 'sɜ:fɪs /

UK / ˈsɚfəs /

A2
  • adjecitve
  • Of the top layer; not deep or meaningful
  • noun
  • Top layer of the ground or of water
  • Nature or emotions that show, but may not be true
  • Outside or upper layer of something
  • verb
  • To give (road) a top layer
  • To appear after being hidden, unseen, or unknown
  • To come to the top of something; emerge
  • To come to the top level of water, mud, etc.

see

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US / si: /

UK / si /

A1
  • verb
  • To go on a date with someone
  • To predict whether something is, or will be true
  • To understand what someone says
  • To use your eyes to look at something
  • To visit a place often for sightseeing or pleasure
  • To visit or meet with someone
  • To find out by waiting or looking
  • To watch (a game, movie or TV show)

last

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US / lɑ:st /

UK / læst /

A1
  • adjecitve
  • Most recent; the latest
  • The one before
  • adverb
  • Final; with nothing following; after all others
  • Most recent; the latest
  • determiner
  • The one at the end
  • verb
  • To remain or continue for a certain period of time

parallel

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US / 'pærəlel /

UK / ˈpærəˌlɛl /

B1
  • adjecitve
  • (Of two lines) at equal distance from each other
  • (Of computer operation) happening at the same time
  • Very similar and often occurring at the same time
  • noun
  • A line on a map a set distance from the equator
  • verb
  • To be equal to, or like, something else
  • To compare

mirror

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US / 'mɪrə(r) /

UK / ˈmɪrɚ /

A2
  • noun
  • Thing with glass surface used to look at yourself
  • An accurate impression or picture of something
  • verb
  • To reflect (an image)
  • To have similar qualities to something else

could

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US / kəd /

UK / kʊd /

A1
  • other
  • Past form of 'can' to mean have ability
  • Used to ask for something politely, or to offer

hallway

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US / ˈhɔ:lweɪ /

UK / ˈhɔlˌwe /

B2
  • noun
  • Interior passage or corridor onto which rooms open

clear

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US / klɪə(r) /

UK / klɪr /

A1
  • adjecitve
  • Empty; without anything in it or on it
  • Being certain and without doubt
  • Being without any streaks, spots, or cracks
  • Easy to understand; well-explained; obvious
  • adverb
  • Completely; entirely; through the whole of
  • Away from; free from
  • verb
  • To recover from or remove a problem
  • To get rid of the entire contents of
  • To give permission for something to happen
  • To make a place or surface empty by removing
  • To prove that someone is not guilty or to blame

onto

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US / ˈɒntə /

UK / ˈɑnˌtu, -tə, ˈɔn- /

A1
  • preposition
  • Towards a certain direction/into a certain area

with

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US / wɪð /

UK / wɪð, wɪθ /

A1
  • preposition
  • As an employee of a certain company
  • Against something or someone
  • By using something as a means
  • Due to; because of
  • Including
  • Possessing as a feature
  • Related to
  • (Of the manner/attitude by which you do something)
  • Used to express that people or things are together

have

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US / həv /

UK / hæv /

A1
  • verb
  • To drink, smoke, eat or use something
  • To experience the effects of something
  • To organize an event, or join in an activity
  • To own, possess, or hold something
  • To cause to happen or produce a particular effect

know

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US / nəʊ /

UK / noʊ /

A1
  • verb
  • To be familiar with a person or place, thing
  • To feel sure or be convinced about something
  • To discover or be aware of something
  • To be able to distinguish
  • To have knowledge of things

behind

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US / bɪˈhaɪnd /

UK / bɪˈhaɪnd /

A1
  • adjecitve
  • Concerning a later or slower time than expected
  • Being in a losing position in a sporting event
  • Being in the past; old fashioned
  • adverb
  • Remaining
  • noun
  • The part of the body that one sits on
  • preposition
  • At or toward the back of someone or something
  • Supporting or helping someone

almost

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US / 'ɔ:lməʊst /

UK / ˈɔlˌmost, ɔlˈmost /

A1
  • adverb
  • Only a little less than, nearly, not quite

hopefully

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US / ˈhəʊpfəli /

UK / ˈhopfəli /

A2
  • adverb
  • In a manner wishing something to happen

sometimes

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US / ˈsʌmtaɪmz /

UK / ˈsʌmˌtaɪmz /

A1
  • adverb
  • Only at certain times; occasionally

most

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US / məʊst /

UK / most /

A1
  • adverb
  • Very; extremely
  • Greatest possible degree
  • pronoun
  • Nearly all of something

where

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US / hwɛə /

UK / hwɛr, wɛr /

A1
  • conjunction
  • At or in the place which
  • In whatever place
  • pronoun
  • Word you use to ask the location of something

owner

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US / ˈəʊnə(r) /

UK / ˈoʊnə(r) /

A1
  • noun
  • Person who owns or has something

another

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US / əˈnʌðə(r) /

UK / əˈnʌðɚ /

A1
  • adjecitve
  • One more, but not this
  • determiner
  • One more added
  • pronoun
  • One more (thing)

and

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US / ənd /

UK / ənd, ən,ænd /

A1
  • conjunction
  • Used to refer to two or more things
  • Plus; in addition; on top of that
  • Used to introduce an action that follows another

lot

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US / lɒt /

UK / lɑt /

A1
  • noun
  • What happens to a person in life from chance; fate
  • A group of people seen together
  • Item for sale at an auction
  • Small area of land used for a purpose e.g. parking

real

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US / rɪəl /

UK / ˈriəl, ril /

A1
  • adjecitve
  • Actually existing or happening, not imagined
  • Being important or special

two

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US / tu: /

UK / tu /

A1
  • number
  • 2

aisle

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US / aɪl /

UK / aɪl /

B2
  • noun
  • Long narrow space between rows of seats

back

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US / bæk /

UK / bæk /

A1
  • adjecitve
  • Farthest from the front e.g. in a classroom
  • adverb
  • Have returned to a place you were before
  • noun
  • The part of a chair that the upper body leans upon
  • Location at the rear of something
  • The reverse of side something
  • Area on the rear of your body
  • verb
  • To bet money on something
  • To go backwards in a car
  • To support and encourage someone or some cause

couple

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US / 'kʌpl /

UK / ˈkʌpəl /

A2
  • noun
  • Two people in a romantic relationship
  • Two of something; two people; a pair
  • verb
  • To join something to something else
  • (Two animals) to engage in sexual relations
  • To put two people or things together

over

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US / 'əʊvə(r) /

UK / ˈovɚ /

A1
  • adverb
  • Finished; no longer happening
  • Towards the ground/away from a standing position
  • noun
  • A set of six consecutive balls bowled in cricket
  • other
  • Finished
  • preposition
  • Showing the relation when a thing is above another
  • On or covering something
  • Above or across something
  • More than you need
  • From one side to the other
  • In the direction of; toward

something

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US / ˈsʌmθɪŋ /

UK / ˈsʌmθɪŋ /

A1
  • adverb
  • In some degree or measure
  • noun
  • a person or thing of some value or consequence
  • pronoun
  • Thing that is not yet known or named
  • Approximately

screen

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US / skri:n /

UK / skrin /

A2
  • noun
  • Wire net in a door or window to keep insects out
  • Displays in a theater on which movies are shown
  • Flat surface on a computer or TV showing images
  • verb
  • To hide or block something from being seen
  • To examine to find something, e.g. best candidate

observe

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US / əbˈzɜ:v /

UK / əbˈzɜ:rv /

A2
  • verb
  • To celebrate a particular holiday/religious event
  • To obey or follow laws, rules, or customs
  • To watch carefully; to make a comment

put

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US / pʊt /

UK / pʊt /

A1
  • phrasal verb
  • to make a light stop shining by pressing or moving a switch
  • verb
  • To move or place a thing in a particular position
  • To rate something in importance or value
  • To write or say something in a certain manner

out

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US / aʊt /

UK / aʊt /

A1
  • adverb
  • No longer stylish (e.g. fashion)
  • Away from home, business, or the usual place
  • In a direction/movement away from inside or center
  • noun
  • Act when a batter cannot continue playing
  • verb
  • To tell people a secret

version

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US / ˈvə:ʃən /

UK / ˈvɚʒən, -ʃən /

A2
  • noun
  • Different way that someone interprets something
  • New or different form of something
  • An updated form of some software

come

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US / kʌm /

UK / kʌm /

A1
  • verb
  • To arrive at a place
  • (Of mail) to be delivered
  • To move toward someone; go with someone
  • To reach a certain point or state

think

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US / θɪŋk /

UK / θɪŋk /

A1
  • verb
  • To have an idea about something without certainty
  • To have an idea, opinion or belief about something

any

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US / 'enɪ /

UK / ˈɛni /

A1
  • adjecitve
  • One, or some, no matter which
  • pronoun
  • One (thing) of many; some

only

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US / ˈəunli /

UK / ˈonli /

A1
  • adverb
  • Just one; just that amount or thing; not more than
  • Not very important or serious
  • Just that type of thing, person
  • Short time ago; not before a certain time
  • conjunction
  • Except; but

from

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US / frəm /

UK / frʌm, frɑm,frəm /

A1
  • preposition
  • Starting at a particular place, time or level

bathroom

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US / ˈbɑ:θru:m /

UK / ˈbæθru:m /

B1
  • noun
  • Room where you take a bath or go to the toilet

correspond

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US / ˌkɒrəˈspɒnd /

UK / ˌkɔ:rəˈspɑ:nd /

B1
  • verb
  • To have similarity or equality with something
  • To write letters or emails to someone

form

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US / fɔ:m /

UK / fɔrm /

A1
  • noun
  • Sports team or person's current winning record
  • Document you complete when making an application
  • Visible shape or style; type; kind
  • verb
  • To organize something such as a club or group
  • To develop; to come into a shape or substance
  • To make something into a particular shape

far

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US / fɑ:(r) /

UK / fɑr /

A1
  • adjecitve
  • A long way away
  • Being a long way away
  • adverb
  • To a large degree or extent

symmetry

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US / ˈsɪmətri /

UK / ˈsɪmɪtri /

B2
  • noun
  • Having parts that are exactly the same

parabola

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US / pəˈræbələ /

UK / pəˈræbələ /

A1
  • noun
  • Plane curve formed by intersecting other planes

opening

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US / ˈəʊpnɪŋ /

UK / ˈoʊpnɪŋ /

A1
  • noun
  • Free job; job you can apply for
  • Action of starting something, e.g. a new business
  • verb
  • To make accessible or able to be used, e.g. road
  • To start the activities or services of a business
  • To make a space or hole appear in something
  • To move or change so that it is no longer closed
  • To start something, e.g. a new business

our

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US / 'aʊə(r) /

UK / aʊr /

A1
  • determiner
  • Belonging to us

maybe

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US / ˈmeɪbi /

UK / ˈmebi /

A1
  • adverb
  • Possibly but not certainly; perhaps

whole

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US / həul /

UK / hol /

A1
  • adjecitve
  • Complete or full; all of
  • Being in a good condition
  • noun
  • Complete amount or sum; total

but

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US / bət /

UK / bʌt,bət /

A1
  • conjunction
  • Used before you say something different, opposite

video

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US / 'vɪdɪəʊ /

UK / ˈvɪdiˌo /

A2
  • adjecitve
  • Of a moving film, with sound
  • noun
  • Recording capturing action with sound
  • verb
  • To make a moving film of, with sound

would

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US / wʊd /

UK / wʊd /

A1
  • other
  • Used to indicate something imagined
  • Used to ask or request something politely
  • Verb used to indicate possibility, request etc.
  • Used to indicate a preference
  • Used to indicate a reaction
  • Indicates something that occurred repeatedly
  • Used to indicate willingness or ability to do

good

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US / ɡʊd /

UK / ɡʊd /

A1
  • adjecitve
  • Proper, appropriate or right
  • (Of an amount) enough; plenty
  • Excellent; high quality
  • Acting well or properly; of moral character
  • In a positive or happy emotional state
  • noun
  • Advantage or benefit

deal

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US / di:l /

UK / dil /

A1
  • verb
  • To cope with something - usually troubles
  • To give (something bad e.g. news) to
  • To buy and sell illegal drugs
  • To give out (cards, etc.) to; distribute
  • To do business with someone or to sell products

principal

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US / ˈprɪnsəpl /

UK / ˈprɪnsəpəl /

A2
  • adjecitve
  • Being the main or most important
  • noun
  • Leading person in a group of musicians or dancers
  • Head teacher of a school
  • Original amount of money borrowed

cloth

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US / klɔθ /

UK / klɔθ, klɑθ /

B1
  • noun
  • Piece of material used for cleaning, etc.
  • Material made by weaving fibers to make clothes

now

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US / naʊ /

UK / naʊ /

A1
  • adverb
  • At the present time or moment
  • Right away or in the next possible moment
  • Used to refer to something that just happened
  • Time between the present and a moment in the past
  • conjunction
  • Resulting from or because of something

convex

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US / ˈkɒnveks /

UK / ˈkɑ:nveks /

C1
  • adjecitve
  • Having a surface that curves outward like a ball

towards

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US / tə'wɔ:dz /

UK / 'təuədz, twɔ:dz /

A1
  • preposition
  • In the direction of someone or something

especially

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US / ɪˈspeʃəli /

UK / ɛˈspɛʃəli, ɪˈspɛʃ- /

A1
  • adverb
  • More than usual; extremely

can

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US / kæn /

UK / kən,kæn /

A1
  • noun
  • A metal container for storing food
  • other
  • Able to; have the skill to; have the time to
  • verb
  • To have permission to
  • To be possible to do
  • To preserve food by sealing it in a metal container

same

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US / seɪm /

UK / sem /

A1
  • adjecitve
  • Being equal in quality and amount
  • Identical; not different
  • Not changing; constant

single

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US / 'sɪŋɡl /

UK / ˈsɪŋɡəl /

A1
  • adjecitve
  • Being one only, without others
  • Only; merely
  • Not married or in a relationship
  • noun
  • One run in cricket or a hit baseball
  • An individual song from a CD or album
  • Person who is not married or in a relationship

not

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US / nɒt /

UK / nɑt /

A1
  • adverb
  • Word indicating the negative
  • (Used to form the negative of verbs)

reflective

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US / rɪˈflektɪv /

UK / rɪˈflɛktɪv /

A2
  • adjecitve
  • Having the ability to reflect light, heat, sound
  • Thinking deeply about something; thoughtful

want

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US / wɔnt /

UK / wɑnt, wɔnt /

A1
  • noun
  • Something you desire or wish for
  • State or condition of poverty
  • verb
  • To desire or wish for something; hope for a thing

care

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US / keə(r) /

UK / kɛr /

A1
  • noun
  • Treatment you receive for your health or safety
  • Something that a person worries about
  • verb
  • To feel interest, concern, or worry
  • To look after someone or something

anyone

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US / ˈeniwʌn /

UK / ˈɛniˌwʌn, -wən /

A1
  • pronoun
  • Any person

again

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US / ə'ɡen /

UK / əˈɡɛn /

A1
  • adverb
  • One more time, once more

bottom

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US / 'bɒtəm /

UK / ˈbɑtəm /

A2
  • adjecitve
  • Concerning the part under something, e.g. a vase
  • noun
  • The part of your body you sit on
  • Lowest position, often in a company or contest
  • Lowest part of something; part on which it rests
  • Lowest level, part or point of an object
  • The part under something, e.g. a vase
  • verb
  • To hit the lowest part of something

about

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US / ə'baʊt /

UK / əˈbaʊt /

A1
  • adverb
  • To be ready to; going to
  • Nearly; approximately; roughly
  • Near; next to; close to
  • In every direction; in the area of
  • preposition
  • Concerning or of (a topic)

case

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US / keɪs /

UK / kes /

A1
  • noun
  • Container used to carry things, e.g. clothes
  • Set of facts about a crime
  • Set of facts about an event
  • Example or instance of something
  • verb
  • To find out about a place, as in planning to steal

what

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US / wɒt /

UK / hwɑt, hwʌt, wɔt, wʌt,hwət, wət /

A1
  • pronoun
  • Thing or things that; the same kind as
  • Used to emphasize something you are about to say
  • adjecitve
  • Used to refer to a particular amount, or number
  • Used to place emphasis on a particular quality
  • adverb
  • To a certain degree
  • determiner
  • Question words used for asking for information
  • exclamation
  • Used to express excitement, shock, or surprise
  • Used to ask people to repeat something they said

get

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US / ɡet /

UK / ɡɛt /

A1
  • verb
  • To become affected by illness or disease
  • To begin to feel or understand an emotion or idea
  • To send or bring someone or something home, etc.
  • To go somewhere to obtain something
  • To (cause to) do a particular thing
  • To obtain, receive or be given something
  • To currently have
  • To prepare for use
  • To understand something being said or read

then

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US / ðen /

UK / ðɛn /

A1
  • adverb
  • A time that is not now
  • Following another thing in time or arrangement
  • Following on reasonably from what was just stated
  • At that time, not now

bunch

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US / bʌntʃ /

UK / bʌntʃ /

B1
  • noun
  • A group of things of the same kind
  • verb
  • To group people or things closely together
  • (Cloth) to gather/be gathered together in folds

type

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US / taɪp /

UK / taɪp /

A1
  • noun
  • Printed letters or blocks used for printing them
  • Group of things or people sharing common features
  • verb
  • To identify something belonging to a group
  • To write by touching keys on a keyboard

interesting

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US / ˈɪntrəstɪŋ /

UK / ˈɪntrɪstɪŋ, -tərɪstɪŋ, -təˌrɛstɪŋ /

A1
  • adjecitve
  • Taking your attention; making you want to know
  • verb
  • To make someone want to know about something
  • To persuade to do, become involved with something

virtual

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US / ˈvɜ:tʃuəl /

UK / ˈvɚtʃuəl /

B1
  • adjecitve
  • Existing only on the internet or on a computer
  • Existing only in a digital world
  • Almost being; nearly complete

shoplift

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US / 'ʃɒplɪft /

UK / 'ʃɒplɪft /

B1
  • verb
  • To steal things from a shop

like

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US / laɪk /

UK / laɪk /

A1
  • adjecitve
  • Being equal in status or kind to something else
  • Similar; the same
  • adverb
  • For example
  • preposition
  • Used as a filler; used to ad emphasis
  • In a way similar to the way something is done
  • Such as; for example
  • verb
  • To want to
  • To find something pleasing; to prefer something

mean

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US / mi:n /

UK / min /

A1
  • adjecitve
  • Being good at
  • Nasty; unkind
  • Not liking to spend money; cheap; stingy
  • noun
  • Average of a set of numbers
  • verb
  • To express a particular idea or thought
  • To intend to do something in particular
  • To have a particular meaning or value

ball

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US / bɔ:l /

UK / bɔl /

A1
  • noun
  • Large dance where people dress formally
  • Small round object often used in a game or sport

example

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US / ɪgˈzɑ:mpl /

UK / ɪɡˈzæmpəl /

A1
  • noun
  • Thing, person which represents a category

that

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US / ðæt /

UK / ðæt, ðət /

A1
  • adjecitve
  • The person or thing being talked about
  • Used to identify something both the speakers know
  • adverb
  • Used to reinforce adjectives and adverbs
  • To such a degree
  • conjunction
  • Used to connect a noun clause
  • Used to introduce an adverbial clause
  • Used to introduce a noun clause
  • determiner
  • Used as a noun to refer to something
  • pronoun
  • Referring an object far away
  • Used to refer to the relative pronoun ‘which’

happen

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US / 'hæpən /

UK / ˈhæpən /

A1
  • verb
  • To take place or occur

find

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US / faɪnd /

UK / faɪnd /

A1
  • noun
  • Object discovered by chance
  • Things that have been discovered from searching
  • verb
  • To become aware of something that is happening
  • To discover or meet by chance
  • To decide if someone is guilty of a crime, or not
  • To learn through study, research, or effort
  • To discover something by looking for it

diffuse

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US / dɪ'fju:z /

UK / dɪˈfjuz /

B2
  • verb
  • To cause something to spread through a large area

people

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US / 'pi:pl /

UK / ˈpipəl /

A1
  • noun
  • Persons sharing culture, country, background, etc.
  • Men, Women, Children

concave

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US / 'kɒn'keɪv /

UK / kɑnˈkev, ˈkɑnˌkev /

C1
  • adjecitve
  • Hollow; curved inward

right

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US / raɪt /

UK / raɪt /

A1
  • adjecitve
  • Correct or true
  • The south side of you looking at the rising sun
  • adverb
  • Exactly in a place or time
  • Being appropriate for a particular event
  • In a straight or direct manner
  • noun
  • Something you are legally or morally allowed to do
  • Ideal of what is just and good
  • Political view based on conservatism
  • verb
  • To fix something previously wrong or unjust
  • To make upright, as a boat that has turned over

how

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US / haʊ /

UK / haʊ /

A1
  • adjecitve
  • To what degree? in what amount?
  • adverb
  • (Used to explain the way to do something)
  • exclamation
  • For what purpose or reason?
  • (Used to ask someone or something's condition)

make

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US / meɪk /

UK / mek /

A1
  • noun
  • Product made by a particular company; brand
  • verb
  • To arrange or prepare something e.g. dinner
  • To get to (a place) on time
  • To gain the status of (teacher, lawyer, etc.)
  • To create something by putting things together
  • To earn a certain amount of money at a job
  • To cause or force a person to do something
  • To cause something to happen or be formed

other

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US / 'ʌðə(r) /

UK / ˈʌðər /

A1
  • adjecitve
  • A thing different from that mentioned
  • determiner
  • (Something) else; not the first (one)
  • pronoun
  • Being the one and only thing of that category

outside

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US / ˌaʊtˈsaɪd /

UK / aʊtˈsaɪd, ˈaʊtˌsaɪd /

A2
  • adverb
  • Beyond the limits or edges of some place, thing
  • noun
  • Area around or near something, such as a building
  • preposition
  • Beyond the limits or edges of some place, thing

kind

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US / kaɪnd /

UK / kaɪnd /

A1
  • adjecitve
  • In a caring and helpful manner
  • friendly and considerate
  • noun
  • One type of thing

you

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US / jʊ /

UK / ju /

A1
  • pronoun
  • Person someone is speaking or writing to
  • Person or people in general

little

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US / 'lɪtl /

UK / ˈlɪtl /

A1
  • adjecitve
  • Being short in length of time
  • Not great in size, amount, or degree; small
  • Being very young or younger than others
  • adverb
  • By an amount or degree that is not very much
  • Not often; rarely
  • noun
  • A person's name

also

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US / 'ɔ:lsəʊ /

UK / ˈɔlso /

A1
  • adverb
  • In addition; too; in a similar way

diverge

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US / daɪˈvɜ:dʒ /

UK / daɪˈvɜ:rdʒ /

B2
  • verb
  • To move away from, in a different direction
  • To think or feel differently about something

this

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US / ðɪs /

UK / ðɪs /

A1
  • adjecitve
  • Used to indicate something already been discussed
  • Used to indicate something happening around now
  • adverb
  • An indication by a physical motion or gesture
  • A specific amount of
  • determiner
  • Person, thing, or idea near you
  • pronoun
  • Person, thing that has already been discussed

although

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US / ɔ:lˈðəu /

UK / ɔlˈðo /

A1
  • conjunction
  • Despite the fact that; however

bowl

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US / bəʊl /

UK / bol /

A2
  • noun
  • Part of an object that has a rounded, inward curve
  • Round container used for holding rice, soup etc.
  • Round Building to watch sports events, concerts
  • Low-lying land with higher ground around it
  • verb
  • To roll a ball in the sport of bowling
  • To throw a ball in a game such as cricket

let

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US / let /

UK / lɛt /

A1
  • verb
  • To allow someone to do something
  • Introducing a suggestion to do something together
  • To rent a house, etc. to others

focal

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US / 'fəʊkl /

UK / ˈfokəl /

B2
  • adjecitve
  • (Of a point) being the main or important one

probably

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US / ˈprɒbəbli /

UK / ˈprɑbəbli /

A1
  • adverb
  • That is likely to happen or be true

will

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US / wɪl /

UK / wɪl /

A1
  • noun
  • Desire or choice of someone
  • Document saying who gets your money when you die
  • Strong desire to do something; determination
  • Desire to do something; strong wish to do
  • other
  • Used with verbs to express the future
  • verb
  • To leave property to someone after your death
  • To use mental effort to make something happen
  • Am (is, are) likely to do
  • To influence someone to do something
  • To make something happen by strongly wanting it

inside

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US / ˌɪn'saɪd /

UK / ɪnˈsaɪd, ˈɪnˌsaɪd /

A2
  • adjecitve
  • Being in something
  • Being in a building
  • adverb
  • Into a house; indoors
  • noun
  • Inner part or surface of something

straight

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US / streɪt /

UK / stret /

A2
  • adjecitve
  • Not having curves, bends, or angles
  • Not gay; heterosexual
  • honest and direct
  • adverb
  • in a line; immediately; honestly and directly

already

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US / ɔ:lˈredi /

UK / ɔlˈrɛdi /

A1
  • adverb
  • Having happened or been done before this time

realize

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US / 'ri:əlaɪz /

UK / ˈriəˌlaɪz /

A1
  • verb
  • To become aware of or understand mentally

imagine

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US / ɪ'mædʒɪn /

UK / ɪˈmædʒɪn /

A1
  • verb
  • To think creatively about; form mental picture of

parabolic

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US / ˌpærə'bɒlɪk /

UK / ˌpærəˈbɑlɪk /

A1
  • adjecitve
  • Having the form of a parabola

diffusely

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US / dɪˈfjuːsli /

UK / dɪˈfjuːsli /

A1
  • other
  • In a diffuse manner

side

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US / saɪd /

UK / saɪd /

A1
  • adjecitve
  • In addition to the central or most important thing
  • Next to, or very close to, the right or left of
  • noun
  • Position or opinion that is opposite to another
  • Right or left part of a person's body
  • Feature of someone's personality
  • Straight edge of an object
  • One of two or more groups fighting each other
  • verb
  • To decide to agree with one point, not the other

once

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US / wʌns /

UK / wʌns /

A1
  • adverb
  • One time; one instance
  • At a time in the past
  • conjunction
  • When; as soon as

corner

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US / 'kɔ:nə(r) /

UK / ˈkɔrnɚ /

A2
  • noun
  • Place where two lines, sides, corners etc. meet
  • Edges of something, e.g. eyes, boxing ring
  • verb
  • To force into a position impossible to escape from
  • To go around a bend in the road (often by driving)

small

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US / smɔ:l /

UK / smɔl /

A1
  • adjecitve
  • Little in size; not big
  • (Of letters) not written in capital letters
  • Being insignificant or minor
  • (Of a business) with few people or things; local
  • (Of voice) being soft and quiet
  • (Of a child) being young

point

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US / pɔɪnt /

UK / pɔɪnt /

A1
  • noun
  • An item to be discussed
  • Small spot or dot
  • Fact or detail
  • Feature of something
  • The size of the text on a page or screen
  • A certain time or stage in a process
  • Certain position in time or space
  • Idea or fact you try to convince people about
  • Measurement of scores in a game, sport
  • Sharp end of something, e.g. a pen or pin
  • verb
  • To face a certain direction, e.g. north
  • To indicate something with your finger to others

axis

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US / ˈæksɪs /

UK / ˈæksɪs /

B1
  • noun
  • A line about which a rotating body turns

guess

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US / ɡes /

UK / ɡɛs /

A1
  • noun
  • Answer given when you don't know if it is correct
  • verb
  • To give an answer without knowing if it is correct

use

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US / ju:s /

UK / ju:s /

A1
  • noun
  • Ability to employ something
  • Need to enable it to work
  • Permission to do something with something
  • Act of spending money
  • Operation of a machine for its function
  • verb
  • To have; to eat, drink, consume etc.
  • To need to operate or work
  • To operate a machine, e.g. a computer
  • To treat a person badly
  • To do something with, for a task or purpose

reason

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US / 'ri:zn /

UK / ˈrizən /

A1
  • noun
  • Ability to think about facts and form a judgment
  • Explanation for why something occurred or was done
  • verb
  • To think and make conclusions in a logical manner

here

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US / hɪə(r) /

UK / hɪr /

A1
  • adverb
  • In this place; at this location, position or time

always

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US / 'ɔ:lweɪz /

UK / ˈɔlwez,-wɪz,-wiz /

A1
  • adverb
  • For a very long time
  • At all times; in every situation
  • For ever

quick

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US / kwɪk /

UK / kwɪk /

A1
  • adjecitve
  • Using very little time; moving far in little time
  • Learning and understanding rapidly and easily

all

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US / ɔ:l /

UK / ɔl /

A1
  • adverb
  • Completely; totally
  • determiner
  • Being every one of something
  • pronoun
  • 100% of something; the complete amount

project

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US / prəˈdʒekt /

UK / prəˈdʒɛkt /

A1
  • noun
  • A planned piece of work for specific purpose
  • Group of homes built by government for poor people
  • verb
  • To predict what will happen in the future
  • To show something on a screen using light
  • To stick out past the edge of something

oppose

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US / əˈpəʊz /

UK / əˈpoʊz /

A2
  • verb
  • To fight against someone in a contest or game

direction

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US / də'rekʃn /

UK / dɪˈrɛkʃən, daɪ- /

A2
  • noun
  • When someone tells people what to do
  • Describes the way you are going, e.g. North

reflect

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US / rɪ'flekt /

UK / rɪˈflɛkt /

A2
  • verb
  • To indicate or be a sign of something
  • To bounce back light, heat, sound from a surface
  • To show an image in glass, water, a mirror etc.
  • To think of something seriously and carefully

they

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US / ðeɪ /

UK / ðe /

A1
  • pronoun
  • Two or more people, animals, or things

look

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US / lʊk /

UK / lʊk /

A1
  • noun
  • Person's beauty or physical attractiveness
  • Particular style of dress, clothes, or appearance
  • The way someone, something appears to be
  • Act of searching for or examining something
  • verb
  • To appear to be; seem

useful

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US / ˈju:sfl /

UK / ˈjusfəl /

A1
  • adjecitve
  • That can help with a particular task

clearly

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US / ˈklɪəlɪ /

UK / ˈklɪrlɪ /

A1
  • adverb
  • In a way that is easy to understand; obviously

show

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US / ʃəʊ /

UK / ʃo /

A1
  • noun
  • False display of love, emotion or action
  • An event for displaying or promoting goods
  • Play, opera or theater production
  • Presentation that is broadcast on TV or radio
  • verb
  • To be easily seen or displayed
  • To display your emotions or feelings
  • To let someone see something; display
  • To explain or teach how something is done
  • To lead someone somewhere; point them to something
  • To prove something to be true, correct
  • To reveal or allow something to be seen

bit

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US / bɪt /

UK / bɪt /

A1
  • noun
  • Device put in a horse's mouth to control it
  • Small piece of something
  • verb
  • (E.g. of fish) to take bait and be caught

take

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US / teɪk /

UK / tek /

A1
  • noun
  • Filming of a single scene for TV or the movies
  • verb
  • To accept something that is offered
  • To use a method of traveling, e.g. a bus or train
  • To use a camera to make (a photo)
  • To pick up something and go away with it
  • To study a subject in school
  • To attempt to pass (an exam)
  • To require a certain amount of time, money, space

way

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US / weɪ /

UK / we /

A1
  • adverb
  • Used to emphasize the amount of something
  • noun
  • Particular aspect of something being thought about
  • One of various choices that could be made
  • Particular existing condition or state
  • (Often long) distance or length of time
  • How something is done
  • Route to go to a place
  • Small street
  • Usual behavior, emotions or habits of someone
  • Subtitles section
  • All the parabolic mirror examples we've been doing so far have been concave.
  • And that just means, you might know already what concave means, but just to make it clear, they were opening out towards the objects, and in most of the cases, out towards where the images were formed.
  • So what we cared about the inside surface of the mirror right here.
  • And the way I always remember concave is the kind of forms that cave.
  • You could view this part right here as the inside of the cave.
  • And we had a bunch of examples where we had focal points.
  • And then this one here was our principal axis.
  • And we had objects.
  • And I showed you how the light would reflect off of the mirror and go through the focal points.
  • So thus we did a bunch of examples like that in the last couple of videos.
  • What I want to do in this video is a quick example of using a convex parabolic mirror.
  • So let's do a convex parabolic mirror.
  • And here we care about the other side of the mirror.
  • We care about the side that's the outside of the bowl, if you want to view the parabolic mirror as a ball.
  • So let's think about that as a little bit.
  • So let's imagine that once again we have something that's the shape of a parabola.
  • It has this-- let me draw a better version of it-- so it has the shape of a parabola.
  • This is the principal axis right over here.
  • You could almost view that as the line of symmetry.
  • This is still the focal point.
  • That right there is still the focus.
  • But now we're going to assume that the reflective surface is on the outside.
  • It's on the outside.
  • So the reflective surface is kind of jutting out towards us as opposed to caving in.
  • That's another way to remember it-- concave, looks like it's caved in.
  • Here, it's jutting out towards us.
  • And let's think about what would happen if I put an object over here on the outside assuming that this is a reflective surface.
  • So if I put an object over here, what is going to happen?
  • So let's just do the same exercise.
  • But what we're going to do is we're going to have one parallel ray.
  • We could do rays that go in any direction from any of these points because there's some light source over here.
  • They never draw the light source, but it reflects diffusely off of this object.
  • So this object is emitting light rays in every direction.
  • But the useful diffused light rays being emitted by this object are the ones that are parallel to the principal axis and the ones that would go through the focus.
  • Let's do one that's parallel.
  • So if something is parallel to the principal axis-- and I'm not doing the map over here-- but if it reflects on the outside of this parabolic mirror, it will reflect in a way so it looks like it's coming from the focus.
  • So I would see the focus as on the other side of this mirror, but it would reflect in a way that it looks like it's coming from the focus.
  • So that ray will reflect like that.
  • And then if we have another ray from the head of this object, from the tip of that arrow, and that ray is going in the direction of the focus-- so the focus is there-- so let me draw the direction.
  • So let's say I have an incident ray going in the direction of the focus.
  • When that gets reflected, it will reflect parallel to the principal axis.
  • And so what type of image is going to be formed here?
  • Clearly, these two rays will never converge.
  • So we can't form a real image.
  • We cannot project that image onto a screen or cloth and then see it.
  • These two rays are converging.
  • But if one were to observe the rays, they look like they are diverging from a single point.
  • This ray looks like, let me make it clear, this one that just got reflected out parallel looks like it's coming from if you go straight back behind the mirror.
  • And then this one that's coming out looks like it's coming out of this point there.
  • So it looks like they're diverging from this point on the other side of the mirror.
  • And not only doesn't look like they're coming from there, but the actual image will look like that.
  • We could do it with other points on this arrow if we want.
  • If you take the bottom of the arrow, that's maybe the easiest, light that goes straight to the actual mirror will then be reflected straight back.
  • So it would look like it's coming from a point at the mirror back over here.
  • And we could do other things.
  • We could draw stuff so that you could see what the whole image-- we could take points over here, and you would say that that would correspond to a point over there.
  • But I guess the thing that hopefully you'll realize from this video is when you're dealing with a convex parabolic mirror, the outside is a reflective surface.
  • You're not going to form a real image, you're going to form a virtual image.
  • This is a virtual image, just like you would see in your bathroom mirror, although that's probably not parabolic, I'm guessing.
  • And it's also going to be a smaller image.
  • And you see these types of mirrors all the time, especially around corners.
  • If you see a corner-- let's let me draw a hallway with corners-- you'll sometimes see mirrors-- let me do it the other way-- you'll sometimes see mirrors so that people-- well, the mirror might be out here-- so that you can see people as they're coming around the corner.
  • And the reason why these mirrors are useful is that they reflect light from a lot of directions.
  • And so you can kind of see around corners.
  • This is not the best of drawing, but I think you've seen these convex mirrors, mirrors that look something like this.
  • Sometimes you'll also see them at the aisles of stores, at the head of aisles of stores.
  • And this way, the store owners can have a good field of view.
  • And they can see if anyone is shoplifting.
  • Anyway, hopefully, you found that interesting.