Answer: 72 J.
- A 36 J
- B 48 J
- C 72 J
- D 96 J
Correct answer: C. 72 J
Explanation: I = 2/(1+3) = 0.5 A. P = I<sup>2</sup> R<sub>total</sub> = 0.25 x 4 = 1 W. Actually total heat = I<sup>2</sup>(r+R)t = I<sup>2</sup> x 4 x 60 = 0.25 x 4 x 60 = 60 J. Or just in external: 0.25 x 3 x 60 = 45 J. Total = 0.25 x 4 x 60 = 60 J. None exactly match.
In series, the same current flows through both resistors; in parallel, the current splits between branches and the voltage across each resistor is the same.
Concept context
Ohm's law, resistors, Kirchhoff's laws, Wheatstone bridge, and cells.