Lenses

Question 1

What are lenses?

Answer 1

Lenses are devices used to change direction of light by refraction. These also focus light

Question 2

What is a converging lens?

Answer 2

One which brings light rays together, making them focus onto one point

Question 3

What is a diverging lens?

Answer 3

One which spreads the light rays out

Question 4

Rays hit the lens……

Answer 4

perpendicular to lens but parallel to principal axis

Question 5

What is a lens axis?

Answer 5

A line going through the lens vertically

Question 6

What is a principal axis?

Answer 6

A line going through the lens horizontally

Question 7

What is a principal focus?

Answer 7

a point onto which the light rays converge

Question 8

What is a focal plane?

Answer 8

A plane parallel to the principal focus?

Question 9

Where do light rays that weren’t perpendicular to the lens go

Answer 9

somewhere else on the focal plane

Question 10

What does a converging lens look like?

Answer 10

cave outward

Question 11

What is a focal length?

Answer 11

distance from lens axis to the focal plane

Question 12

Focal length is positive for?

Answer 12

real images - converging lens

Question 13

What is a focal length negative for?

Answer 13

virtual images - diverging and converging

Question 14

What does a diverging lens look like?

Answer 14

Caves inwards

Question 15

What is the principal focus on a diverging lens?

Answer 15

a point from which the light rays appear to have come from (as long as they’re parallel)

Question 16

Images created by lens can be …

Answer 16

real and virtual

Question 17

What is a real image?

Answer 17

the light rays are actually there and can be captured on a screen. A real image is defined as one that is formed when rays of light are directed in a fixed point.

Question 18

a converging lens can create both…

Answer 18

real and virtual images

Question 19

What is a virtual image?

Answer 19

light rays aren’t where they appear to be, so image cannot be captured on screen

Question 20

If the object is further than the focal length away from lens then what image is formed?

Answer 20

real image

Question 21

What about if closer?

Answer 21

virtual image

Question 22

does a diverging lens ever form a real image?

Answer 22

None

Question 23

lens equation

Answer 23

1/u + 1/v = 1/f 
where  
f = focal length 
u = distance to lens axis from object
v = distance from image to principal focus (this is negative for virtual images)

Question 24

What is the power of the lens?

Answer 24

lens ability to bend light. measured in dioptres.

greater power means more refraction

Question 25

Equation for power?

Answer 25

1/ focal length

Question 26

when do lenses work together?

Answer 26

when in series - pt = p1 + p2 +p3

Question 27

What is the equation for magnification?

Answer 27

m = v/u
where
v = image height or v
u = object height or u