Question

Assertion: In case of a concave mirror, if a point object is moving towards the mirror till focus along its principal axis, then its image will move away from the mirror.
Reason: In case of reflection $($along the principal axis of mirror$)$, object and image always travel in opposite directions.
Consider the spherical mirror to be stationary and choose the correct option.

• A. Assertion and Reason are true and the reason is the correct explanation of the assertion
• B. Assertion and Reason are true and the reason is not the correct explanation of the assertion
• C. Assertion is true, but reason is false.
• D. Assertion is false, but reason is true.

Answer 1

The correct option is A Assertion and Reason are true and the reason is the correct explanation of the assertion

For a stationary spherical mirror-
Velocity of the image when the object is moving along the principal axis is given by,
$v_i=-m^2{v}_o$, where $v_o$ is the object velocity.
The negative sign shows that object and image always travel in the opposite direction.
Also, when the object is kept till the focus of the concave mirror, its real image on the same side of the mirror is formed. Thus, the image moves away from the mirror as the object is moved closer to the mirror.
But, when the object is between pole and focus of the mirror, then its virtual image on the other side of the mirror is formed.
Thus, the image comes closer to the mirror as the object is moved closer to the mirror.
Hence, option $\left(a\right)$ is correct.

Why this question? Caution: Always remember that object and image travels opposite to each other only in parallel direction to the principal axis when the spherical mirror is at rest.