KCL Section 5: Thin Lens Equation (Waves and Photons)

Question 1

When measuring distances on lens diagrams what does
u =
v =
f =

Answer 1

u = distance from the lens to the object 
v = distance from the lens to the image
f = distance from the lens to the focal point

Question 2

Remember to make the value ______ if it is virtual

Answer 2

Remember to make the value negative if it is virtual

Question 3

What is the equation?

Answer 3

1 1 1
– + – = –
u v f

Question 4

Where is an image produced when placing an object 6 cm away from a convex lens of focal length 3 cm?

Answer 4

1/6 + 1/v = 1/3

1/6 + 1/6 = 1/3

v = 6
The image is 6cm away. It is real and inverted.

Question 5

What image is produced by placing an object 4 cm away from a convex lens of focal length 8 cm?

Answer 5

1/4 + 1/v = 1/8
1/4 + -1/8 = 1/8
v = -8cm

Question 6

If an object is 6 cm from a concave lens with focal length f = −3 cm, what is its position and nature?

Answer 6

1/6 + 1/v = -1/3
-1/3 - 1/6 = -1/2
v = -2cm
v is virtual and upright