A doorbell circuit runs from a 12 V supply. The buzzer coil's resistance is 48 Ω. How big a current flows through the coil?
Ohm's law gives the current: I = V/R. Here, for the first time, it does the arithmetic for a real circuit.
The doorbell's buzzer coil has 12 V across it and a resistance of 48 Ω. Calculate the current through the coil.
Write down the values in the question:
V = 12 V
R = 48 Ω
I = ?
Write down the equation:
I = V/R
Substitute in the values:
I = 12/48
Simplify:
I = 0.25 A
How many ohms is a resistance of 4.7 kΩ?
The conversion is its own numbered step inside the same three-step solve, written before the equation is used.
The doorbell's indicator board has a 2.0 kΩ resistor with 9.0 V across it. Calculate the current through the resistor.
Write down the values in the question:
V = 9.0 V
R = 2.0 kΩ
I = ?
Convert the resistance to ohms:
R = 2.0 × 1000 Ω = 2000 Ω
Write down the equation:
I = V/R
Substitute in the values:
I = 9.0/2000
Simplify:
I = 0.0045 A
Six in a row now. Work each one on paper, in the three steps, before you answer.
A 30 Ω resistor has 6.0 V across it. Enter the current in A.
A 60 Ω coil has 24 V across it. Enter the current in A.
A 180 Ω resistor has 4.5 V across it. Enter the current in A.
A 240 Ω element has 120 V across it. Enter the current in A.
A 3.0 kΩ resistor has 9.0 V across it. Enter the current in A.
A 250 Ω resistor has 7.5 V across it. Enter the current in A.
A 40 Ω motor coil in a garage-door opener has 18 V across it. Enter the current through the coil in A.
A 2.4 kΩ resistor on a thermostat board has 12 V across it. Enter the current in A.
In the circuit shown, what current does the ammeter read? Enter it in A.