Answer: 60 W bulb.
- A 100 W bulb
- B 60 W bulb
- C Both equally bright
- D Neither lights up
Correct answer: B. 60 W bulb
Explanation: In series, same current flows. R100 = 2002/100=400. R60 = 2002/60=667. Higher R means more power dissipated: P=I2R. 60W bulb has more R, so it's brighter.
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.