# power through a resistor question

Discussion in 'General Electronics Chat' started by hunterage2000, May 12, 2010.

1. ### hunterage2000 Thread Starter Active Member

May 2, 2010
402
0
Can someone tell me how to find power in different resistors once you have the total power?

2. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
Depends on the particular circuit you are considering - do you have something specific in mind?

3. ### hunterage2000 Thread Starter Active Member

May 2, 2010
402
0
lets say 4 parallel resistors R1 = 5 R2 = 7 R3 = 10 R4 = 20 and V = 10.

4. ### Bosparra Member

Feb 17, 2010
79
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You need to calculate the current through every resistor and multiply with the voltage across it.

May 11, 2010
241
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Current is V/R, and then you're multiplying by V to get power, so you can simplify it to V^2 / R.

For the 5 Ohm for example, (10 V ^2) / 5 Ohms = 20 W

6. ### guru200773 Member

Apr 26, 2010
94
1
you are wrong Mr.sage.radachowsky.. U have to find out the voltage drop on each resistor in order to use that V^2/R formula not the source voltage..Whatever the formula u want use u need the current.. so I=V/R(eq). R(eq)=R(1)+R(2)+R(3)+R(4)=5+7+10+20=42
therefore.. I=10/42=0.238A.. Use P=I^2*R formula i.e
power on R(1) = 0.2822, power on R(2)=0.3965, power on R(3)=0.5664 power on R(4) =1.1328 Add the all power in each resistor then total power is P(t)=2.3779--------------------- eq(1)

another of finding total power is P(t)= V(source)*I=10*0.238=2.38-------------------- eq(2)
both eq(1) and eq (2) are equal [eq(1)sightly varies because of rounding off of decimal points in calculations....]

If u know the total power and source Voltage.. find current by using I=P(t)/V
then use formula I^2/R to find the power drop on resistor.....

Last edited: May 12, 2010