# Conceptual Questions Lenz's Law, Solenoid

1. May 10, 2013

### devilaudy

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

https://www.dropbox.com/s/17hsoz0zdfoston/Screen shot 2013-05-10 at 12.37.44 PM.png

1) A voltage is applied to a solenoid such that a current is flowing in the indicated direction. Inside the solenoid is a single wire loop that is oriented in the same direction as the solenoid windings.

Which one of the following statements is true in the case where the voltage applied to the solenoid is increased?
a) The magnetic field of the solenoid points to the left while the induced current at location A points out of the paper.
b) The magnetic field of the solenoid points to the right while the induced current at location A points into the paper.
c) The magnetic field of the solenoid points to the left while the induced current at location A points into the paper.
d) The magnetic field of the solenoid points to the right while the induced current at location A points out of the paper.

2) Which one of the following statements is true in the case where the voltage applied to the solenoid is increased?
a) The magnetic dipole moment of the loop points to the right.
b) The torque on the loop points into the paper.
c) The torque on the loop points out of the paper.
d) The magnetic dipole moment of the loop points to the left.
e) A voltage is only induced in the inner loop, not in the solenoid itself.

2. Relevant equations

Lenz's law

3. The attempt at a solution

I thought the answer to question 1 was c) since the magnetic field would point in the opposite direction to fight the increase in magnetic flux, but it was wrong. I have no idea where to start for the second question. Thanks in advance!!
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. May 10, 2013

### barryj

A to part 1, wrap your hand around the wire around the solonoid. Where do the fingers point?

3. May 10, 2013

### devilaudy

To the right. I know how to use the right hand rule, but in this situation I am confused with the loop inside the solenoid. The magnetic field inside the solenoid points to the right, but how does that affects the current inside the loop? Would the current at location A point outside the paper?

4. May 10, 2013

### barryj

What does Lenz law state? Something like the current would oppose the change in the field?