What is the Focal length of a plane mirror?

Answer 1

Infinity.because the distance of object from mirror"p" and the distance from image to mirror"q" are equal,so by using formula

1/f=1/p+1/q

we can find the answer

as the image of plane mirror is virtual,so"q" is taken negative,so putting values

1/f=1/p-1/p(bcz p=q)

1/f=0

f=1/0

and any thing divided by zero is infinity.