Answer: 4.5 W.
- A 2.25 W
- B 4.5 W
- C 9 W
- D 18 W
Correct answer: B. 4.5 W
Explanation: Max power when R = r = 2 Ω; I = 6/4 = 1.5 A; P = I²R = 2.25·2 = 4.5 W.
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.