The Placement of Bulb in a Torch's Concave Reflector

Understanding the Placement of Bulb in a Torch's Concave Reflector

A torch is a common handheld device used to provide illumination in various situations, such as in the dark or during emergencies. One key component of a torch is its concave reflector, which plays a crucial role in directing and focusing the light emitted by the bulb.

When it comes to the placement of the bulb in the concave reflector of a torch, there are several options to consider:

(a) between the pole and focus of reflector

(b) at the focus of reflector

(c) between focus and centre of curvature of reflector

(d) at the centre of curvature of reflector

Final answer: In a torch, the bulb is placed at the focus of the concave reflector. When the bulb is positioned at the focus, the light gets reflected off the mirror and travels in parallel rays, providing a strong beam of light. This configuration takes advantage of the unique property of concave mirrors where all parallel light rays reflect through the focus.

Explanation: In a torch, the bulb is placed at the focus of the concave reflector. This is because the reflector is a concave mirror designed to convert diverging light from the bulb into a parallel beam of light. The parallel beam is useful as it allows the light to be focused over a greater distance and area.

For example, assume you turn on a torch in the dark. The light rays diverging from the bulb get reflected by the concave mirror and become parallel after reflection, focusing the light forward.

Concave mirrors have a unique property, where all rays parallel to its principal axis (an imaginary line passing through the center of the mirror) reflect and pass through a common point, known as the focus. Hence, placing the bulb at the focus ensures a strong and directed beam of light.