Home PYQs UPPSC UPPSC MCQs Prelims 2008 (GS Paper I)

Question

Electric motors operating at low voltages tend to burn out because

  1. they draw more current which is inversely proportional to the voltage
  2. they draw more current which is inversely proportional to the square root of the voltage
  3. they draw heat proportional to v2
  4. low voltage sets in electrical discharge

Answer:

Option A: they draw more current which is inversely proportional to the voltage

Detailed Solution:

The correct answer is “they draw more current which is inversely proportional to the voltage”.

When the voltage decreases, the motor compensates by drawing more current to maintain the same power output. Power (P) is the product of current (I) and voltage (V), expressed as:

𝑃=𝑉×𝐼

For a fixed power requirement, if the voltage (V) decreases, the current (I) increases proportionally.

The increased current leads to more heat dissipation due to resistance in the motor's wiring, which follows Joule's law:

Heat∝I2×R

Thus, operating at low voltage leads to overheating and potential burnout.