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Physics Question - Current in Resistor of parallel circuit - Need Help!?
Cannot see why it isn't 0.65. I worked out that the current for both parallel circuit and the 9 Ohm resistor is 0.75. So 32/37*0.75 =0.65 but it says it's incorrect. The hints don't help at all, so I was hoping someone could help me? Thank you

4 Answers
- billrussell42Lv 73 years agoFavorite Answer
The three R's in parallel are equivalent to
1/R = 1/5 + 1/12 + 1/20
1/R = 0.2 + 0.083 + 0.05 = 0.333
R = 3 Ω
add 9 in series to get 12 Ω
I = e/R = 9/12 = 0.75 amp
that produces a voltage across the 3 in parallel of
E = IR = 0.75 x 3 = 2.25 volts
and the currents in the 3 branches are
I = E/R
I = 2.25/5 = 0.45 amp
I = 2.25/12 = 0.1875 amps
I = 2.25/20 = 0.1125
(the three should add up to 0.75 amps)
PS, the circuit is drawn poorly, the junctions have to be shown clearly, see below.

- electron1Lv 73 years ago
The 5 Ω, a 12 Ω, and a 20 Ω resistor are in parallel with each other.
1/Req = 1/5 + 1/12 + 1/20 = ⅓
Req = 3 Ω
Total resistance = 9 + 3 = 12 Ω
B. I = 9 ÷ 12 = 0.75 amps
Let’s use the following equation to determine the voltage for the 9 Ω resistor.
V = I * R = 0.75 * 9 = 6.75 volt
To determine the voltage for each of the resistors in parallel, subtract this number from 9.
V = 9 – 6.75 = 2.25 volts
I 5 = 2.25 ÷ 5 = 0.45 amp
I 12 = 2.25 ÷ 12 = 0.1875 amp
I 20 = 2.25 ÷ 20 = 0.1125 amp
To check these currents, the sum should be 0.75 amps.
Sum 0.45 + 0.1875 + 0.1125 = 0.75
- Robert JLv 73 years ago
The total current is 0.75A as you say.
The currents in the branches are:
5R: 0.45A
12R: 0.1875A
20R: 0.1125A
Sanity check: 0.45 + 0.1875 + 0.1125 = 0.75
- Anonymous3 years ago
Try 1.8 but I’m not sure it’s right



