Question

A student constructed a simple electric circuit where two light bulbs were connected in parallel. The circuit power source was a 6.0-V cell. One of the light bulbs had a resistance of 25 ohms, and the other had a resistance of 50 ohms. What was the combined resistance of the light bulbs in the circuit?
a) 75ohms

b) 42ohms

c) 25ohms

d) 17ohms

Answer 1

Answer:

RT =  17 ohms

Explanation:

For two parallel resistances in a circuit the combined resistance is given by:

$\frac{1}{R_T}=\frac{1}{R_1}+\frac{1}{R_2}\\\\\frac{1}{R_T}=\frac{R_2+R_1}{R_1R_2}\\\\R_T=\frac{R_1R_2}{R_1+R_2}$

R1 = 25 ohms

R2 = 50 ohms

You replace the values of R1 and R2 in the formula for RT:

$R_T=\frac{(25)(50)}{25+50}ohms=16.66\ ohms \approx 17\ ohms$

hence, the combined resitances is 17 ohms