Question

3. [1pt]
A headlamp in a car has a bulb in front of a concave mirror with radius of curvature C. At what distance should the bulb be placed from the mirror if the reflected rays are to be well collimated (i.e., parallel)? E.g., enter A.

You have 2 tries. Don't just guess! You should be able to explain your reasoning in terms of principal rays. Drawing a diagram will be helpful.

1. 
   
2. 2C
3. 3C
4. C
5. C/4
6. C/2

Answer 1

The bulb should be at a distance equal to focal length to become reflected rays parallel to axis.

Focal length of concave mirror is half the radius of curvature.

Focal length = C/2

option F is correct