Question

for a concave mirror , paraxial rays are focused at distance R/2 from pole and marginal rays are focused at a distance x from pole then

x=R/2

2) x=-f

3) x R/2

4) x

Answer 1

We know that Focus in a concave mirror is given by the formula

f= R/2 ( where f is the focus and R is the radius of curvature)

When parallel rays are focused at a distance R/2 from the pole that is right hand side to the mirror then the marginal rays are focused on the left hand side of the mirror which will be given by -f

So the correct option is

2. X= -f