Question

Why does an electric bulb become dim when an electric heater in parallel circuit is switched ON?

Hint:

More appliances ON → More current → Voltage drop → Bulb dims.

Answer 1

Why Does an Electric Bulb Become Dim When an Electric Heater in Parallel Circuit is Switched ON?

In a household electrical circuit, appliances such as bulbs and heaters are usually connected in parallel. Ideally, in a parallel circuit, each appliance receives the same voltage. However, when a high-power device like an electric heater is switched ON, the bulb may appear dim. This happens due to practical limitations in the supply system.

Detailed Explanation:

1. High Current Draw by Heater:
An electric heater has low resistance and high power rating. When it is switched ON, it draws a large amount of current from the mains.

2. Voltage Drop in Supply Wires:
Due to the heavy current drawn by the heater, a voltage drop occurs in the connecting wires (because wires also have some resistance). As a result, the effective voltage across the bulb decreases slightly.

3. Reduced Brightness of Bulb:
The brightness of a bulb depends on the power it receives, and power is proportional to the square of voltage (P ∝ V²). Even a small decrease in voltage reduces the power supplied to the bulb, making it glow dimly.

4. Effect in Real Circuits:
Although in an ideal parallel circuit voltage remains constant, in real-life household circuits internal resistance of wires and supply lines causes slight voltage variations.

Conclusion:
When an electric heater is switched ON in a parallel circuit, it draws a large current, causing a small voltage drop in the supply lines. This reduces the voltage across the bulb, decreasing its power and making it appear dim.