Question

A student conducts an activity using a concave mirror which focal length of 10 cm . He placed the object 20cm from the mirror. Where is the image likely to form? *

At 10cm in front of the mirror
At 10cm behind of the mirror
At 20cm behind the mirror
At 20cm in front of the mirror

Answer 1

At 20cm in front of the mirror

We know that center of curvature = 2F

given focal length to be 10cm

Therefore center of curvature = 2 x 10 = 20cm

Now we know that the object distance from the mirror is 20 cm, that means the object is kept at the center of curvature, and we know that when the object is kept at center of curvature, the image is also always formed at the center of curvature only and is real and inverted

Therefore it would be 20cm in front of the mirror

HOPE IT HELPS

Answer 2

Given: A student conducts an activity using a concave mirror which has a focal length of 10 cm. He placed the object 20cm from the mirror.

To find: The position of the image.​  

Solution:

• The position of the image formed by a concave mirror can be found by using the formula,

        $\frac{1}{v} + \frac{1}{u} = \frac{1}{f}$

• Here, v is the distance of the image formed and u is the distance of the object from the concave mirror.

        $\frac{1}{v} + \frac{1}{20 cm} = \frac{1}{10 cm}$

        $\frac{1}{v} = \frac{1}{20}$

        $v = 20 cm$

• Since the distance of the image is positive, it is concluded that the image is formed behind the concave mirror.

Therefore, the position of the image is 20 cm behind the mirror.