Question

In torches, searchlights, and headlights of vehicles, the bulb is placed

• A. between the pole and the focus of the reflector
• B. very near to the focus of the reflector
• C. between the focus and center of curvature of the reflector
• D. at the center of curvature of the reflector

Answer 1

The correct option is B

very near to the focus of the reflector

The explanation for the correct Option:

Option (B):

1. Inside a bulb there generally is a concave reflector.
2. For a concave mirror, when an object is placed at its focus, after reflection from the mirror, it reflects a parallel beam of light that goes to infinity.
3. Hence, in torches, searchlights, and headlights of vehicles, the bulb is placed very near to the focus of the reflector.

The explanation for the Incorrect Option:

Option (A):

1. When an object is placed between the pole and the focus of a concave mirror, the image formed is magnified, virtual, and behind the mirror.
2. An image formed that is magnified, virtual, and behind the mirror cannot give a maximum output of light rays.
3. Hence, in torches, searchlights, and headlights of vehicles, the bulb is not placed between the pole and the focus of the reflector.

Option (C):

1. When an object is placed between the focus and center of curvature of a concave mirror, the image formed is inverted and magnified.
2. An image formed that is inverted and magnified cannot give a maximum output of light rays.
3. Hence, in torches, searchlights, and headlights of vehicles, the bulb is not placed between the focus and center of curvature of the reflector.

Option (D):

1. When an object is placed at the center of the curvature of a concave mirror, the image formed is inverted.
2. An image formed that is inverted cannot give a maximum output of light rays.
3. Hence, in torches, searchlights, and headlights of vehicles, the bulb is not placed at the center of the curvature of the reflector.

Hence option B is correct.