A magnetic field is perpendicular to a 0.0387 m x 0.0599 m rectangular coil of w

Question

A magnetic field is perpendicular to a 0.0387 m x 0.0599 m rectangular coil of wire that has 109 turns. In a time of 0.0525 s, an average emf of magnitude 1.66 V is induced in the coil. What is the magnitude of the change in the magnetic field?

A neon sign requires 10000 V for its operation. It operates from a 220 V receptacle. What must be the turns ratio Ns/Np of the transformer?

In some places, insect "zappers", with their blue lights, are a familiar sight on a summer's night. These devices use a high voltage to electrocute insects. One such device uses an ac voltage of 4360 V, which is obtained from a standard 120 V outlet by means of a transformer. If the primary coil has 18 turns, how many turns are in the secondary coil?

Explanation / Answer

A transformer has 500 turns in the primary coil and 300 turns in the secondary coil. If the primary is connected to 220 V mains, what voltage will be obtained from the secondry coil? What type of transformer is this?

To evaluate the magnitude of the voltage in the secondary coil:
Es/Ep = Ns/Np
Es = (Ep*Ns)/Ns
= (200*300)/500
= 132 volts. This shows that the transfor is a step down transformer because the number of volts in the primary is greater than that in secondary. I.e 220v > 132v

I also know something about the turns ratio. If the turns ratio of the transformer is greater than 1, the transformer is secondary transformer. If the turns ratio of the transformer is less than 1, the transformer is primary transformer.

Transformer equation:
N2 / N1 = V2 / V1

N2 / 20 = 4325V / 120V

So N2 = 721 turns

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