Lens and Telescopes Quiz

Question 1

Where does refraction happen?

Answer 1

at the boundary/interface between different materials with different densities

Question 2

How do you measure the focal length of a converging lens using a distant object?

Answer 2

1. Place lens on a track. Place white card at other end
2. Place track at window, lights off.
3. Move card till image focuses
4. Measure length between lens and card.

a paper / screen (between
the objective and the
eyepiece) (1)
• move screen/lens (to and
fro) (1)
• to obtain an image which is
in focus / clear / sharp (1) 
measure the {distance /
space} (1)
• between lens and {paper /
image} (1)

Question 3

Explain how a simple telescope’s eyepiece magnifies a distant object

Answer 3

the eyepiece, at a wider angle, spreads the rays / magnifies the real image that the convex lens creates, inside the tube, to produce the virtual image seen

the (objective) lens (1)
• collects light (from Jupiter) (1)
• focuses/converges/refracts the
light (1)
• (objective) produces a real
image (1)
• (at the) focal point (1)
• (Image is viewed by the)
eyepiece lens (1)
• (Eyepiece) produces a virtual
image (1) 
magnifies the image (produced
by the objective) (1)

Question 4

What are convex lens also known as?

Answer 4

converging (e.g objective lens)

Question 5

Explain how waves are refracted at boundaries

Answer 5

Entering the the denser material causes the rays to slow their speed and direct/ refract towards the normal at the boundary

ray of light passing from air
into glass
air: ray angled towards the normal on boundary
Glass: ray angled away from normal

Question 6

Where are waves reflected?

Answer 6

at the boundary/interface between different materials

Question 7

Explain how a reflecting telescope works?

Answer 7

1. Large concave mirror collects reflects and converges parallel rays
2. Convex mirror reflects and converges rays from the concave mirror infront of its focal point
3. Rays converge through a small hole in the larger mirror to for a real image behind it
4. The converging eyepiece lens magnifies this image

Reflecting telescope has
mirror(s) (1)
Reflecting telescope can gather more light / can have a larger objective (1)
Image viewed from the side of reflecting telescope (1)