A hair dryer's heating wire carries 6.0 A when 120 V is across it. Nothing on the label states the wire's resistance. Ohm's law can tell you anyway.
Start from Ohm's law: I = V/R. This time the unknown is the resistance R, so make R the subject.
Multiply both sides by R: I × R = V. Then divide both sides by I: R = V/I.
The three solving steps stay exactly the same: write down the values and mark the unknown, select the correct equation, substitute in the values and simplify.
The hair dryer's heating wire carries 6.0 A with 120 V across it. Calculate the wire's resistance.
Write down the values in the question:
V = 120 V
I = 6.0 A
R = ?
Write down the equation:
I = V/R
Make R the subject:
R = V/I
Substitute in the values:
R = 120/6.0
Simplify:
R = 20 Ω
A resistor carries 0.30 A with 9.0 V across it. Enter its resistance in Ω.
A lamp carries 0.60 A with 24 V across it. Enter its resistance in Ω.
When a current arrives in mA, convert it to amperes before substituting. The conversion is its own numbered step, exactly as before.
The dryer's indicator lamp carries 250 mA with 6.0 V across it. Calculate the lamp's resistance.
Write down the values in the question:
V = 6.0 V
I = 250 mA
R = ?
Convert the current to amperes:
I = 250/1000 A = 0.25 A
Write down the equation:
R = V/I
Substitute in the values:
R = 6.0/0.25
Simplify:
R = 24 Ω
Four more. Work each one on paper first; R = V/I goes straight into step 2.
A resistor carries 50 mA with 12 V across it. Enter its resistance in Ω.
A buzzer carries 0.040 A with 6.0 V across it. Enter its resistance in Ω.
A coil carries 0.20 A with 18 V across it. Enter its resistance in Ω.
A sensor carries 0.025 A with 4.5 V across it. Enter its resistance in Ω.
An aquarium pump motor carries 0.25 A with 15 V across it. Enter the motor's resistance in Ω.
A night-light carries 20 mA with 7.0 V across it. Enter its resistance in Ω.
In the circuit shown, what is the resistor's resistance? Enter it in Ω.