A clothes dryer's heating element carries 25 A, and its resistance is 9.6 Ω. P = I²R gives the power it dissipates in one step.
P = I²R gives the power dissipated in a resistance from the current through it and its resistance. The calculation runs the same three steps as every power calculation.
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 clothes dryer's heating element carries 25 A and has a resistance of 9.6 Ω. Calculate the power it dissipates.
Write down the values in the question:
I = 25 A
R = 9.6 Ω
P = ?
Write down the equation:
P = I²R
Substitute in the values:
P = (25)²(9.6)
Simplify:
P = (625)(9.6)
P = 6000 W
The dryer element dissipates 6000 W.
A heating wire of 8.0 Ω carries 3.0 A. Enter its power in watts.
A supply lead of 0.4 Ω carries 5.0 A. Enter its power in watts.
A 20 Ω test resistor carries 1.5 A. Enter its power in watts.
The same dryer's drum motor windings carry 4.0 A and have a resistance of 2.5 Ω. Calculate the power dissipated in the windings.
Write down the values in the question:
I = 4.0 A
R = 2.5 Ω
P = ?
Write down the equation:
P = I²R
Substitute in the values:
P = (4.0)²(2.5)
Simplify:
P = (16)(2.5)
P = 40 W
The element dissipates 150 times the windings' power. The square on the current does most of that work.
A camper's 0.8 Ω heater element carries 15 A. Enter its power in watts.
A rheostat set to 35 Ω carries 2.0 A. Enter its power in watts.
A motor winding of 1.2 Ω carries 10 A. Enter its power in watts.
A 15 Ω resistor carries 4.0 A. Calculate the power it dissipates, in W.
A 6.0 Ω element carries 8.0 A. Calculate the power it dissipates, in W.
A 100 Ω resistor carries 0.5 A. Calculate the power it dissipates, in W.