http://www.ck12.org Chapter 13. Electric Circuits: Batteries and Resistors
Answer:P=IV, so the total power equals the total voltage multiplied by the total current. Thus,
Ptotal=ItotalVtotal= ( 2. 2 A)( 20 V) = 44. 4 W. So the Power Supply outputs 44W (i.e. 44 Joules of energy per
second).
Question:How much power is each resistor dissipating?Answer:Each resistor has different current across it, but the same voltage. So, using Ohm’s law, convert the power
formula into a form that does not depend on current.P=IV=
(V
R)
V=V
2
R SubstitutedI=V/Rinto the power
formula.P 90 Ω=V
902 Ω
R 90 Ω=( 20 V)^2
90 Ω =^4.^4 W;P^10 Ω=V 102 Ω
R 10 Ω=( 20 V)^2
10 Ω =^40 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 current is flowing through each resistor?
Answer:Use Ohm’s law to calculate the current for each resistor.I 90 Ω=
V 90 Ω
R 90 Ω
=
20 V
90 Ω
= 0. 22 A I 10 Ω=
V 10 Ω
R 10 Ω
=
20 V
10 Ω
= 2. 0 A
Notice that the 10Ωresistor has the most current going through it. It has the least resistance to electricity so this
makes sense.
∗Note: If you add up the currents of the individual ’rivers’ you get the total current of the of the circuit, as you
should.Watch this Explanation
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