2.3 Lenses

Question 1

Lens

Answer 1

piece of transparent material that refracts light rays to form an image

Question 2

principal axis

Answer 2

imaginary horizontal line running through optical centre of lens

Question 3

2 types of lens

Answer 3

convex/converging
concave/diverging

Question 4

convex/converging lens

Answer 4

converges rays of light travelling parallel to its principal axiS

Question 5

focal point of converging/convex lens

Answer 5

point where rays converge

Question 6

focal length

Answer 6

distance from focal point to optical centre of lens

Question 7

concave/diverging lens

Answer 7

diverges rays of light travelling parallel to principal axis

Question 8

focal point of diverging/concave lens

Answer 8

point where rays appear to diverge from

Question 9

lens equation

Answer 9

1/f = 1/u + 1/v

Question 10

what do the letters in the lens equation stand for?

Answer 10

u = object to lens
v = image to lens
f = focal length of lens

Question 11

lens equation method

Answer 11

move lens until image is sharply focused
measure u, distance from object to lens and v, distance from image to lens
repeat to obtain series of 5 values for u and v
calculate 1/u and 1/v

Question 12

refraction rules for converging lens - ray going to optical centre of lens

Answer 12

straight through
no refraction

Question 13

refraction rules for converging lens - ray travelling parallel to principal axis

Answer 13

refracts
travels through focal point of lens

Question 14

refraction rules for converging lens - ray passes through focal point on way to lens

Answer 14

refract
travel parallel to principal axis

Question 15

refraction rules for diverging lens - ray going to optical centre of lens

Answer 15

straight through
no refraction

Question 16

refraction rules for diverging lens - ray travelling towards focal point on opposite side of lens

Answer 16

refracts
travels parallel to principal axis

Question 17

refraction rules for diverging lens - ray travelling parallel to principal axis

Answer 17

refracts
appears to have come from focal point on object side of lens

Question 18

Convex lens - object beyond 2f from lens example

Answer 18

camera

Question 19

Convex lens - object beyond 2f from lens properties

Answer 19

image is:
real
inverted
diminished
between F and 2F

Question 20

Convex lens - object at 2f example

Answer 20

photocopier

Question 21

Convex lens - object at 2f properties

Answer 21

image is:
real
inverted
same size as object
at 2F

Question 22

Convex lens - object between F and 2F example

Answer 22

projector

Question 23

Convex lens - object between F and 2F properties

Answer 23

image is:
real
inverted
enlarged/magnified
beyond 2F

Question 24

Convex lens - object at F

Answer 24

no image will be formed here as the rays are parallel to each other

Question 25

Convex lens - object between F and the lens example

Answer 25

magnifying glass

Question 26

Convex lens - object between F and the lens properties

Answer 26

image is: virtual upright magnified between F and 2F

Question 27

Concave lens properties

Answer 27

image is: virtual upright diminished between F and the lens

Question 28

Magnification of lens equation

Answer 28

image size/object size image distance (v)/object distance (u) himage/hobject

Question 29

Magnification of lens

Answer 29

compare distance of object to optical centre of lens with distance of image to optical centre of lens

Question 30

sign conventions for f

Answer 30

- for convex + for concave

Question 31

sign conventions for v

Answer 31

+ for real image and opposite side of lens - for virtual image and object's side of lens

Question 32

power of lens unit

Answer 32

diopters D

Question 33

power of lens equation

Answer 33

1/focal length (m)

Question 34

power of concave diverging lens

Answer 34

negative

Question 35

power of convex/converging lens

Answer 35

positive

Question 36

What type of lens is in the eye?

Answer 36

Convex/converging lens

Question 37

Near point

Answer 37

Closest distance at which eye can focus on an object

Question 38

Near point for normal eye

Answer 38

25cm

Question 39

Far point

Answer 39

Furthest point that the eye can focus on

Question 40

Far point for normal eye

Answer 40

Infinity

Question 41

Accomodation

Answer 41

Adjustment that the eye makes to change the power of a lens so that there is a sharp image on the retina

Question 42

2 defects of vision

Answer 42

Myopia Hypermetropia

Question 43

Myopia

Answer 43

Short sighted Far objects appear blurred Light rays converge at a point before reaching the retina instead of focusing on the retina Image of far objects formed in front of retina

Question 44

Causes of myopia

Answer 44

Cornea curved too much Lens is too powerful Eye linger than usual

Question 45

Correction of myopia

Answer 45

Diverging/concave lens

Question 46

U and v values for myopia

Answer 46

Lens must produce image of object at infinity at person’s far point U = far point - infinity V = person’s unaided far point - negative as virtual and on same side as object

Question 47

Hypermetropia

Answer 47

Long sight Nearby objects appear blurred, distance objects = clearer Light rays would not converge until point behind retina

Question 48

Hypermetropia causes

Answer 48

Lens in eye not powerful enough Eye shorter than normal

Question 49

Hypermetropia correction

Answer 49

Converging/convex lens

Question 50

U and v values for Hypermetropia

Answer 50

Far point = infinity Near point = more than 25cm Corrective lens used to make object at 25cm appear (virtual image) at near point U = 25cm V = - (their near point) - negative as virtual image