# Calculating time in which flux changes

1. Dec 16, 2011

### jitznerd

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

If the magnetic flux linking all the turns of a 50 turn coil changes from 10mWb to 20mWb and induces an emf of 62.5V in the coil, calculate the time over which the flux changes.

2. Relevant equations

e=Nd x change in flux / dt

3. The attempt at a solution

Not sure if this is correct formula but transposed formula to:

t = Number of turns x Change in flux / e

= 50 x 10 / 62.5

t = 8s

2. Dec 16, 2011

### Staff: Mentor

Could you do it one more time, this time showing the units? Your answer may be correct (seems kind of long), but it would be much clearer if you showed units (and included exponents with numbers like milliWebers...)

3. Dec 17, 2011

### jitznerd

Yeah I thought 8 seconds seemed a long time, thats what made me query if I had gone about it right.

The question is typed exactly as I have been given with those units, then I have used what I think is Faradays law:

E (volts) = N (number of turns) x change in flux (Webers) / Time (s)

Then transposed this to:

Time = N (number of turns) x change in flux (Webers)/ E (volts)

This gave me the 50 x 10 / 62.5 = 8 seconds.

I initially went used:

Change in time = change in flux (Webers) / E (volts)
= 10/62.5 = 0.16 secs (this answer seemed a little more realistic although it hadnt brought the 50 turns into the equation.

4. Jun 9, 2013

### britbat

try a change in flux of 10 mWb (0.01 Wb)

5. Jun 11, 2013

### rude man

The change in flux is not 10 Wb. It's 10 mWb.