# Homework Help: Question about induced e.m.f

1. May 21, 2015

### anonymousZ10

1. The problem statement, all variables and given/known data
Based on what i've got, i guess the answer is A. However, I'm not quite sure of myself.
From what I can see coil Y has its own magnetic field because current is flowing in that coil. When theres a flow of current there will be a magnetic field around it. Thus, placing coil Y close to coil X will produce induced e.m.f on coil X.

The main problem here is how to determine the direction of current flow in coil X ?

well, please correct me if my theory was incorrect
2. Relevant equations

3. The attempt at a solution

2. May 21, 2015

### BvU

Hi Z,

You are searching in the right direction and now need something to go by: an equation perhaps ? Could you post the most relevant ?
What determines the induced emf ? And its polarity ?

3. May 21, 2015

### anonymousZ10

i've checked the answer just now, guess what, the right answer is B :D
Would you care to help me find the reason why is this
I just don't get it

4. May 21, 2015

### BvU

Well, I tried to help in post #2. THe questions still stand!

Approaching from the other end: what happens when the switch is opened ?

5. May 21, 2015

### anonymousZ10

I'm still trying to figure out what happens when the switch is opened. lol

6. May 21, 2015

### BvU

Well, you already said it in so many words:
and what happens to current when that switch opens ?

Oh, the questions from post # 2 Are still open !