KCL Section 5: Lenses (Lenses)

Question 1

What is the focal point?

Answer 1

The focal point is the point where parallel incident rays of light meet or appear to diverge from.

Question 2

Do converging lenses have a real focal point?

Answer 2

Converging lenses have a real focal point, which means that the focal point actually exists, and the image formed at the focal point could be projected onto a screen.

Question 3

Another word for a converging lens?

Answer 3

Convex

Question 4

Another word for a diverging lens?

Answer 4

Concave

Question 5

Do diverging lenses have a real focal point?

Answer 5

Diverging lenses have a virtual focal point - the rays don’t actually intersect at this point, but they appear to, when you look at the refracted rays

Question 6

Take a 5 minute break and rate the card 5

Answer 6

:-)

Question 7

What is the focal length?

Answer 7

The focal length is the distance between the optical centre (the centre of the lens) and the focal point.

Question 8

Power of a lens?

Answer 8

1 / focal length

Question 9

A lense has a focal length of 46cm. What is the power?

Answer 9

2.17 D

Question 10

A concave lens has a virtual focal length of 36.4 cm. What is the power?

Answer 10

-2.75 D

Question 11

Calculate the power of a converging lens with a focal length of 6.5 cm

Answer 11

15 D

Question 12

Calculate the power of a converging lens with a focal length of 48 mm

Answer 12

21 D

Question 13

Calculate the power of a converging lens with a focal length of 32.5 cm

Answer 13

3.08 D

Question 14

Calculate the power of a diverging lens with a focal length of 7.8 cm

Answer 14

-13 D

Question 15

Calculate the power of a diverging lens with a focal length of 51.5 mm

Answer 15

-19.4 D

Question 16

Calculate the focal length of a converging lens with a power of 4.0 D

Answer 16

0.25 m

Question 17

Calculate the focal length of a converging lens with a power of 2.90 D

Answer 17

0.34 m

Question 18

Calculate the focal length of a converging lens with a power of 3.15 D

Answer 18

0.32 m

Question 19

Calculate the focal length of a diverging lens with a power of -3.4 D

Answer 19

-0.29 m

Question 20

Calculate the focal length of a diverging lens with a power of -0.56 D

Answer 20

-1.79 m

Question 21

f a combination of two or more lenses is used, the total power is the ______ of the powers of the lenses.
Remember the the focal length, and therefore the power, of a diverging lens is ________.

Answer 21

f a combination of two or more lenses is used, the total power is the sum of the powers of the lenses.
Remember the the focal length, and therefore the power, of a diverging lens is negative.

Question 22

Converging lens (1D) and a converging lens of power 2D are put together. What is the new power?

Answer 22

1 + 2 = 3

3D

Question 23

Calculate the combined power two converging lenses with a focal lengths of 12 cm.

Answer 23

17 D

Question 24

Calculate the combined power of a convex lens with a focal length of 9.0 cm and another convex lens with a focal length of 3.0 cm.

Answer 24

43 D

Question 25

Calculate the combined power of a convex lens with a focal length of 5.0 cm and another convex lens with a focal length of 85 mm.

Answer 25

32 D

Question 26

Calculate the combined power two diverging lenses with a focal lengths of 15 cm.

Answer 26

-13 D

Question 27

Calculate the combined power of a concave lens with a focal length of 67 mm and a convex lens with a focal length of 48 mm.

Answer 27

5.9 D

Question 28

Calculate the combined power of a concave lens with a focal length of 135 mm and a convex lens with a focal length of 80.5 mm.

Answer 28

5.01 D