# Transformer Problem Help

• candyq27

## Homework Statement

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 4270 V, which is obtained from a standard 122.0 V outlet by means of a transformer. If the primary coil has 23 turns, how many turns are in the secondary coil?

E=-NAcos0(B/t)
V=IR
I=(V-E)/R
-B/T=V1/N1=V2/N2
V1/V2=N1/N2
I2/I1=N1/N2

## The Attempt at a Solution

I'm confused about how to do this problem. I know all those formulas but I'm not sure which one to use. I'm not sure which voltage to use and what the two voltages would be. Please help. Thanks!

You are given two voltages (primary and secondary) and the number of turns on the primary winding. Use the formaula that contains a voltage ratio and a turns ratio to find the number of turns on the secondary.

Hint -- use your 2nd to last equation. You are given a voltage ratio, and you need to calculate the required turns ratio.

Doh! marcusl beat me to the punch!

Fastest typing hands in the west!

Thanks
so is the primary voltage the 122 or the 4270?
The equation is either 122/4270=23/x x= 805 OR
4270/122=23/x x= 0.657

The 805 turns makes more sense so that must be right. Thanks!

(listens for the sound of marcusl's keyboard...)

Yes, you are making a step-up transformer. The primary is usually the input side of the transformer, and the secondary is the output side. Your intuition is correct.

I was sleeping that time, Berkeman :zzz: