A transformer has 840 primary turns and 120 secondary turns. What is Vp/Vs?
A doorbell transformer runs from the 120 V house supply. Its primary has 1200 turns; its secondary has 160 turns. What voltage does the bell get?
The transformer equation answers it. Here is the routine, the same one this course uses for every equation.
1. Write down the values in the question, and mark the unknown.
2. Write down the equation: Vp/Vs = Np/Ns. When the unknown is not already the subject, make it the subject before substituting.
3. Substitute in the values, and calculate.
The doorbell transformer: Vp = 120 V, Np = 1200 turns, Ns = 160 turns. Calculate Vs.
Write down the values in the question:
Vp = 120 V, Np = 1200, Ns = 160, Vs = ?
Write down the equation:
Vp/Vs = Np/Ns
Make Vs the subject:
Vs = Vp × Ns/Np
Substitute in the values, and calculate:
Vs = 120 × 160/1200
Vs = 16 V. The bell runs at 16 V.
The same house's thermostat transformer reads Vs = 24 V across its secondary. Ns = 150 turns, Np = 750 turns. Calculate Vp.
Write down the values in the question:
Vs = 24 V, Ns = 150, Np = 750, Vp = ?
Write down the equation:
Vp/Vs = Np/Ns
Make Vp the subject:
Vp = Vs × Np/Ns
Substitute in the values, and calculate:
Vp = 24 × 750/150
Vp = 120 V. That is the house supply.
Here are six solves. Four ask for the secondary voltage, two for the primary.
A phone charger's transformer: 120 V across 600 primary turns; 25 secondary turns. What is Vs, in V?
A transformer has 500 primary turns, 75 secondary turns, and a 120 V supply. What is Vs, in V?
A tube amplifier's transformer has 200 primary turns, 500 secondary turns, on 120 V. What is Vs, in V?
A transformer gives 10 V across its 40-turn secondary. Its primary has 320 turns. What is Vp, in V?
A microwave's transformer has 240 primary turns and 4400 secondary turns, on 120 V. What is Vs, in V?
A lab transformer's secondary reads 150 V across 600 turns. Its primary has 240 turns. What is Vp, in V?
A heater in a workshop runs from a 120 V outlet through a transformer with 800 primary turns and 3200 secondary turns. What voltage does the heater get, in V?
A welding transformer's secondary gives 30 V across 90 turns. The primary has 1080 turns. What is the primary voltage, in V?
A drone-charging pad's transformer has 750 primary turns and 225 secondary turns, plugged into a 120 V outlet. What voltage reaches the pad, in V?