Determine the total resistance of each of the following parallel circuits. (You can calculate the total resistance from the current and voltage using Ohm’s law, or use the Ohmmeter to measure the resistance directly.)

Question

A. A parallel circuit with a 20-ohm resistor and a 10-ohm resistor. 6.7 ohm
B. A parallel circuit with two 20-ohm resistors and a 10-ohm resistor. 5 ohm

C. A parallel circuit with a 15-ohm light bulb and a 20-ohm resistor. _____

D. A parallel circuit with two 100-ohm resistors and a 20-ohm resistor.___

E. A parallel circuit with a 10-ohm, 20-ohm, 100-ohm and 200-ohm resistor. _____

I tried to complete A and B, but I got stuck on the rest. Can anyone help me out!?

Answer 1

C. A parallel circuit with a 15-ohm light bulb and a 20-ohm resistor. _____
It does not matter if it is a light bulb. Its resistance is 15 ohms.
1/R = 1/15+ 1/20 = 20/300 + 15/300 = 35/300
so
R = 300/35 = 8.57 ohms

Answer 2

D. 1/R = 2/100 +1/20 = 2/100 + 5/100 = 7/100
so R = 100/7 = 14.3 ohms

Answer 3

E. 1/R = 1/10 + 1/20 + 1/100 + 1/200
= 20/200 + 10/200 + 2/200 + 1/200 = 33/200
so R = 200/33 = 6.06 Ohms