Why does an electric bulb fail to glow if the filament is broken, even when the switch is in the 'ON' position?

Correct Option

The correct option is

The electric circuit is incomplete.

Explanation

For an electric current to flow and energize a device such as a bulb, there must be a continuous, unbroken conducting path connecting the terminals of the power source. This continuous path is known as a closed circuit.

Option Analysis

• The potential difference becomes zero. is Incorrect: The potential difference (voltage) is maintained by the power source regardless of the circuit's state. Even with a broken filament, the potential difference exists across the break, but current cannot flow to utilize it.
• The resistance of the circuit becomes infinite. is Incorrect: While an open circuit effectively has infinite resistance, the primary physical reason for the failure to glow is the lack of continuity in the conducting path. "Infinite resistance" is a mathematical consequence of the gap, whereas the "incomplete circuit" describes the structural cause.
• The electric circuit is incomplete. is Correct: A broken filament creates a physical gap in the wire, resulting in an open circuit or incomplete circuit. Without a complete loop, charge carriers (electrons) cannot circulate, and no electrical energy is converted into light and heat.
• The power source is short-circuited. is Incorrect: A short circuit implies a path of near-zero resistance that bypasses the load, causing excessive current flow. A broken filament creates a break (infinite resistance), which is the opposite condition of a short circuit.

Key Takeaway: An electric bulb requires a closed circuit to function. A broken filament breaks the continuity of the path, creating an open circuit and preventing current flow.