13.3. Resistors in Series http://www.ck12.org
Question:How much power does each resistor dissipate?Answer:Each resistor has different voltage across it, but the same current. So, using Ohm’s law, convert the power
formula into a form that does not depend on voltage.
P=IV=I(IR) =I^2 R.
P 90 Ω=I 902 ΩR 90 Ω= ( 0. 2 A)^2 ( 90 Ω) = 3. 6 W
P 10 Ω=I 102 ΩR 10 Ω= ( 0. 2 A)^2 ( 10 Ω) = 0. 4 W
∗Note: If you add up the power dissipated by each resistor, it equals the total power outputted, as it should–Energy
is always conserved.
Question:How much voltage is there across each resistor?
Answer:In order to calculate voltage across a resistor, use Ohm’s law.V 90 Ω=I 90 ΩR 90 Ω= ( 0. 2 A)( 90 Ω) = 18 V
V 10 Ω=I 10 ΩR 10 Ω= ( 0. 2 A)( 10 Ω) = 2 V
∗Note: If you add up the voltages across the individual resistors you will obtain the total voltage of the circuit, as
you should. Further note that with the voltages we can use the original form of the Power equation(P=IV), and
we should get the same results as above.P 90 Ω=I 90 ΩV 90 Ω= ( 18 V)( 0. 2 A) = 3. 6 W
P 10 Ω=I 10 ΩV 10 Ω= ( 2. 0 V)( 0. 2 A) = 0. 4 W
Watch this Explanation
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