Question

a circuit contains two devices that are connected in parallel. if the resistance of one of these devices is 12 ohms and the resistance of the other device is 4 ohms, the total resistance of the two devices is a. 0.333 ohms. b. 16 ohms. c. 0.0625 ohms. d. 3 ohms.

Answer 1

Answer

Formula

Resistance for parallel circuit.

$\frac{1}{R_{Total}} = \frac{1}{R_{1}} +\frac{1}{R_{2}}$

As given

A circuit contains two devices that are connected in parallel.

if the resistance of one of these devices is 12 ohms and the resistance of the other device is 4 ohms.

$R_{1} = 12\ ohms$

$R_{2} = 4\ ohms$

Put in the above

$\frac{1}{R_{Total}} = \frac{1}{R_{1}}+\frac{1}{R_{2}}$

$\frac{1}{R_{Total}} = \frac{1}{12}+\frac{1}{4}$

L.C.M of (12,4)= 12

$\frac{1}{R_{Total}} = \frac{1 + 3}{12}$

$\frac{1}{R_{Total}} = \frac{4}{12}$

$R_{Total} = \frac{12}{4}$

$R_{Total} = 3\ ohms$

Therefore the total resistance of the two devices is 3 ohms .

Option (b) is correct .

Answer 2

R= 1/(1/12+1/4) = 3 ohms