Question

Someone who really understands electricity concepts - help me out! I describe the problem in detail on my site
http://www.romakoulikov.com/another-ohms-law-question-that-stumped-me/

Answer 1

The question focuses on the energy consumed by the lamp, not the entire system.

Use the following formulas:
\[V = IR\]\[P = I^2R\]\[E = Pt = I^2Rt\]
First Situation: Timer has no resistance. Lamp has resistance R.

Total Voltage: V
Total Resistance: R
Total Current: I

Resistance of Lamp: R
Current through Lamp: I
Energy Consumed: E

Second Situation: Timer has resistance R. Lamp has resistance R.

Total Voltage: V
Total Resistance: 2R
Total Current: V/2R = I/2

Resistance of Lamp: R
Current through Lamp: I/2
Energy Consumed: E/4

Therefore, the energy consumed in the second situation is 1/4 the energy consumed in the first answer. The correct choice is C - it will be 1/4 as great.

Answer 2

Thank you very much physmath96. Got it!