Question

To practice problem-solving strategy 26.1 resistors in series and parallel. two bulbs are connected in parallel across a source of emf e = 11.0 v with a negligible internal resistance. one bulb has a resistance of 3.0 Ï , and the other is 3.0 Ï . a resistor r is connected in the circuit in series with the two bulbs. what value of r should be chosen in order to supply each bulb with a voltage of 2.4 v ?

Answer 1

Emf e = 11
r 1 = 3.0
r 2 = 3.0
r 3 = ?

The two in parallel are equivalent to 3 • 3/6 = 1.5 Ω 
To have 2.4 volts across them, the current is I = 2.4/1.5 = 1.6 amps. and the unknown R = (11–2.4) / 1.6 = 5.375 Ω or 5.4 Ω