A transformer has 900 primary turns and 300 secondary turns. Is it step-up or step-down?
In the last lesson you sorted transformers by comparing turns and voltages. The comparison is exact: one equation fixes it.
Consider a transformer with 500 primary turns and 100 secondary turns. Dividing the turn counts gives 500/100 = 5.
The two voltages hold the same number: the primary voltage is five times the secondary voltage.
Vp is the voltage across the primary coil, and Vs is the voltage across the secondary coil. Both are measured in volts.
Np is the number of turns on the primary coil, and Ns is the number of turns on the secondary coil. A turn count is a plain number with no unit.
Careful with the symbols: Np and Ns count turns. They are not the N that labels a magnet's north pole. This course never swaps them.
In symbols, for that transformer: Np/Ns = 500/100 = 5, so Vp/Vs = 5.
The units agree on both sides: volts divided by volts is a plain number, and a turn count divided by a turn count is a plain number.
A diagram of a bar magnet labels its ends N and S. In the transformer equation Vp/Vs = Np/Ns, which of these does Np stand for?
Which unit do the turn counts Np and Ns carry?
A transformer has 150 primary turns and 450 secondary turns. How do its voltages compare?
Write down the equation:
Vp/Vs = Np/Ns
Substitute in the values:
Vp/Vs = 150/450
Simplify the fraction:
Vp/Vs = 1/3
The primary voltage is a third of the secondary voltage. The secondary voltage is three times the primary voltage.
A transformer's primary voltage is twice its secondary voltage. What is Np/Ns?
Write down the equation:
Vp/Vs = Np/Ns
The voltage ratio is given:
Vp/Vs = 2
The turns ratio equals the voltage ratio.
Np/Ns = 2.
A transformer has 840 primary turns and 120 secondary turns. What is Vp/Vs?
Which equation relates a transformer's voltages to its turn counts?
A transformer has 1200 primary turns and 300 secondary turns. Which statement follows from the transformer equation?
Which symbol stands for the voltage across the secondary coil?