A transformer gives 10 V across its 40-turn secondary. Its primary has 320 turns. What is Vp, in V?
A hobby-shop charger must give 12 V from the 120 V supply. Its primary has 2400 turns. How many turns does the secondary need?
Same equation, new unknown: this time the missing value is a turn count.
1. Write down the values in the question, and mark the unknown.
2. Write down the equation: Vp/Vs = Np/Ns. Make the unknown turn count the subject.
3. Substitute in the values, and calculate.
A turn count is a plain number: the answer is a number of turns.
The hobby-shop charger: Vp = 120 V, Vs = 12 V, Np = 2400 turns. Calculate Ns.
Write down the values in the question:
Vp = 120 V, Vs = 12 V, Np = 2400, Ns = ?
Write down the equation:
Vp/Vs = Np/Ns
Make Ns the subject:
Ns = Np × Vs/Vp
Substitute in the values, and calculate:
Ns = 2400 × 12/120
Ns = 240 turns.
Another transformer in the shop must give 30 V from the 120 V supply; its secondary has 500 turns. Calculate Np.
Write down the values in the question:
Vp = 120 V, Vs = 30 V, Ns = 500, Np = ?
Write down the equation:
Vp/Vs = Np/Ns
Make Np the subject:
Np = Ns × Vp/Vs
Substitute in the values, and calculate:
Np = 500 × 120/30
Np = 2000 turns.
Here are six solves. Four ask for the secondary's turn count, two for the primary's.
A transformer must give 6 V from 120 V. Its primary has 900 turns. How many secondary turns?
A shop-machine transformer must raise 120 V to 480 V. Its primary has 350 turns. How many secondary turns?
A transformer gives 10 V across its 50-turn secondary from a 120 V supply. How many primary turns?
A transformer must give 24 V from 120 V. Its primary has 850 turns. How many secondary turns?
A transformer gives 40 V across its 260-turn secondary from a 120 V outlet. How many primary turns?
A bench supply feeds 60 V into a transformer with 320 primary turns. The output must be 12 V. How many secondary turns?
An amplifier's transformer runs from a 120 V outlet and must give 21 V. Its primary has 400 turns. How many turns does the secondary need?
A sign shop's transformer steps 120 V up to 3000 V for a neon tube. Its secondary has 5000 turns. How many turns does the primary have?
A garage-door opener's transformer gives 24 V across its 140-turn secondary from a 120 V supply. How many turns does the primary have?