12th Class Physics Ray Optics Question Bank MCQs - Ray Optics and Optical Instruments

The focal length of a concave mirror is f. An object is placed at a distance x from the focus. The magnification is

A) \[f\,+\,x)\,/\,f\]

B) \[f\,/\,x\]

C) \[x\,/\,f\]

D) \[f\,/\,(f\,+\,x)\]

Correct Answer: B

Solution :

Option [b] is correct.

Explanation: \[u=f+x\]

Using mirror formula,

\[1\,/\,v\,\,+\,\,1\,/\,u\,\,=\,\,1\,/\,f\]

\[\therefore \,\,v=-f(f\,+\,x)\,/\,x\]

So, the magnification \[=\,\,\,|m|\,\,=\,\,\,v\,/\,u\,\,\,=\,\,\,f\,/\,x\]