Correct Option
The correct option is (a).
Explanation
An electric bulb glows due to the heating effect of electric current. When current passes through the bulb's filament, it heats up to a high temperature and emits light (incandescence). For the bulb to glow, the current must be strong enough to generate sufficient thermal energy.
Statement-wise Analysis
- Statement 1 is Correct: Liquids (electrolytes) are generally weaker conductors of electricity compared to metals. Consequently, the current flowing through a liquid tester circuit may be weak. If the current is too weak, the filament does not get heated to a sufficiently high temperature to emit visible light, even though the liquid is conducting electricity. In such cases, a magnetic compass needle or an LED is often used to detect the weak current.
- Statement 2 is Incorrect: Tight and secure connections ensure that the circuit is complete and resistance is minimized. This condition facilitates the glowing of the bulb. Loose connections would be a reason for the bulb not to glow, but the statement specifies that connections are tight.
- Statement 3 is Incorrect: An intact filament is a requirement for the bulb to function. If the filament were broken (fused), the circuit would be incomplete, and the bulb would not glow. Since the statement mentions the filament is intact, this is not a reason for the failure of the bulb to glow.
Key Takeaway: An incandescent bulb requires a specific threshold of current to produce enough heat for light emission. In circuits with weak conductors (like certain liquids), the current may flow but remain insufficient to activate the bulb, necessitating the use of LEDs or magnetic needles for detection.