# Current and Voltage in a transformer

1. Apr 12, 2012

### btpolk

1. The problem statement, all variables and given/known data

The primary coil in a transformer has a power of 100W. The flux through a single loop in the primary is changing at a rate of 25 Wb/s. The primary has 100 loops and the secondary has 500 loops. Assuming a perfect transformer (no losses), determine the current and voltage in both the primary and secondary.

2. Relevant equations

V1/V2=N1/N2=I2/I1

???

3. The attempt at a solution

V1/V2=1/5→5V1=V2

I1/I2=5→5I2=I1

I have no knowledge of an equation/relationship between Wb/s and the other variables in this problems nor can I find one. Please Help.

2. Apr 12, 2012

### Staff: Mentor

A hint can be found in the units: A Weber (Wb) has the equivalent units of V*s (that is, one Weber is a Volt-second).

Given the rate of change 25 Wb/s for a single loop, what's the voltage on the primary?

3. Apr 12, 2012

### btpolk

So it would be 25W then?

4. Apr 12, 2012

### btpolk

i mean 2500W since its per loop

5. Apr 12, 2012

### Staff: Mentor

Sorry, I don't understand your response. Your given information states that there is 100W associated with the primary. What's this 2500W you're proposing? Or do you mean 2500V? That would be a reasonable value

So, if the voltage on the primary is 2500V, what's the current?

6. Apr 12, 2012

### btpolk

Sorry, I did mean 2500V.

So to find the current I would use

P=V1I1

which would mean that the current would have to equal 1/25 A

7. Apr 12, 2012

### Staff: Mentor

Yes. Now, how will you find the secondary voltage and current?

8. Apr 12, 2012

### btpolk

5V1=V2

V2=12500V

P=I2V2

I2=1/125 A

Is that right?

9. Apr 12, 2012

### Staff: Mentor

Your results look good.

10. Apr 12, 2012

### btpolk

Thanks for the help! I really appreciate it