Physics 2015 JAMB Past Questions - Question 34: A real image three times the size of an object is formed 24 cm from a converging mirror. What is the focal length of the mirror?

Correct Answer

C

Explanation

To find the focal length of the mirror, we can use the mirror formula:

1/f = 1/v - 1/u

Where:
f is the focal length of the mirror,
v is the image distance,
u is the object distance.

Given that the real image is three times the size of the object, we can assume that the magnification (m) is 3. The magnification is given by:

m = -v/u

Since the image is real, the image distance (v) is positive. Therefore, we have:

3 = -v/u

Simplifying, we get:

v = -3u

Given that the image distance (v) is 24 cm, we can substitute this value into the equation:

24 = -3u

Solving for u, we find:

u = -8 cm

Now, we can substitute the values of v and u into the mirror formula:

1/f = 1/24 - 1/(-8)

Simplifying further:

1/f = 1/24 + 1/8

1/f = (1 + 3)/24

1/f = 4/24

1/f = 1/6

Therefore, the focal length of the mirror is 6 cm.