In the video, we saw how to calculate a component's power — the energy it transfers each second — from the current through the component and the voltage across it.
P is the power, in watts (W). I is the current through the component, in amperes (A). V is the voltage across the component, in volts (V).
Every power calculation runs the same three steps.
Step 1 — write down the values in the question, and mark the one you want.
Step 2 — write down the equation.
Step 3 — substitute in the values, and simplify. The result line carries the unit: power comes out in watts.
A car's rear-window defroster carries 15 A with 12 V across it. Calculate the power delivered to the defroster.
Write down the values in the question:
I = 15 A
V = 12 V
P = ?
Write down the equation:
P = IV
Substitute in the values:
P = (15)(12)
Simplify:
P = 180 W
The defroster transfers 180 J of energy every second.
So, to find a component's power, multiply the current through it by the voltage across it. Values, equation, substitute, simplify — every power calculation runs those same steps.
A blender carries 4.5 A at 120 V. Enter its power in watts.
A doorbell chime carries 0.25 A at 16 V. Enter its power in watts.
An e-scooter motor carries 7.5 A at 36 V. Enter its power in watts.
An aquarium heater carries 0.6 A at 120 V. Enter its power in watts.
A microwave carries 10 A at 120 V. Enter its power in watts.
A USB desk light carries 0.9 A at 5.0 V. Enter its power in watts.