Learn Ohm's law, how to combine resistors in series and parallel, and how to calculate electrical power and energy.
At constant temperature, the current through a conductor is directly proportional to the voltage across it:
A resistor has 12 V across it and 2 A flowing through it. Find its resistance.
R = V/I = 12/2 = 6 Ω
Find the total resistance of two 4 Ω and 6 Ω resistors connected in series.
R = 4 + 6 = 10 Ω
Find the total resistance of a 6 Ω and a 3 Ω resistor connected in parallel.
1/R = 1/6 + 1/3 = 1/2, so R = 2 Ω
A device draws 2 A at 10 V. Find its power.
P = V × I = 10 × 2 = 20 W
A 100 W bulb runs for 5 hours. How much energy does it use, in kWh (units)?
Energy = Power × time = (100 × 5) / 1000 = 0.5 kWh
1. Using V=IR, find R if V=20V and I=4A.
2. Find the series combination of 2 Ω, 3 Ω, and 5 Ω resistors.
3. Find the parallel combination of two equal 10 Ω resistors.
4. Using P=VI, find the power of a device with V=5V and I=3A.
5. Is total resistance in a parallel combination always less than the smallest individual resistor?