Question

How will a ray of light traveling parallel to the principle axis of a concave mirror be reflected back

Answer 1

It will be reflected to the principal focus of the concave mirror

Step-by-step explanation:

This is because all rays parallel and close to the principal axis of a concave mirror get reflected to the principal focus of the mirror.

For a ray to be parallel to the mirror, it must be coming from an infinite distance.

So, using the mirror formula,

1/u + 1/v = 1/f where u = object distance from mirror, v =image distance form mirror and f =focal length of mirror.

Since u = infinite distance = ∞

1/u + 1/v = 1/f

1/∞ + 1/v = 1/f

0 + 1/v = 1/f

1/v = 1/f

v = f

So, the image is at the principal focus.

So, the ray of light parallel to the principal axis of the concave mirror is reflected to the principal focus of the concave mirror.