Physics 2009 JAMB Past Questions - Question 32: An object is placed 5cm from the pole of a concave mirror . If the focal length of the mirror is 10 cm, what is the image distance?

Correct Answer

C

Explanation

To find the image distance for an object placed in front of a concave mirror, you can use the mirror equation, which is given by:

1/f = 1/v + 1/u

Where:
- f is the focal length of the mirror.
- v is the image distance (positive for real images, negative for virtual images).
- u is the object distance (positive for objects in front of the mirror, negative for objects behind the mirror).

In your case, the focal length of the concave mirror is -10 cm (negative because it's a concave mirror), and the object distance (u) is -5 cm (negative because the object is placed in front of the mirror).

Now, plug these values into the mirror equation:

1/(-10) = 1/v + 1/(-5)

Simplify the equation:

-1/10 = 1/v - 1/5

Now, add 1/5 to both sides to isolate 1/v:

-1/10 + 1/5 = 1/v

To add these fractions, find a common denominator, which is 10:

-1/10 + 2/10 = 1/v

Now, combine the fractions:

1/10 = 1/v

To solve for v, take the reciprocal of both sides:

v = 10

So, the image distance (v) is 10 cm. The positive sign indicates that the image is a real image located 10 cm in front of the concave mirror.