# Physics magnetic fields question

Can anyone provide any guidance on this multiple choice question? I am very confused.

A coil P is connected to a cell and a switch. A closed coil Q is parallel to P and is arranged on the same axis. Which describes the force acting on Q after the switch is closed?
A: Steady and directed to the left
B: Steady and directed to the right
C: Short lived and directed to the left
D: Short lived and directed to the right
(edited 1 year ago)
I hate magnetism (recently learned it at school 💀)

So, to the best of my knowledge, when the coil is connected to a cell and a current goes through it a magnetic field is created. It would be the same for Q and P shouldn’t it?

Would those magnetic fields interact? Possibly.

Are there any options you can discount? And would drawing a diagram help?
Original post by pauline222
Can anyone provide any guidance on this multiple choice question? I am very confused.

A coil P is connected to a cell and a switch. A closed coil Q is parallel to P and is arranged on the same axis. Which describes the force acting on Q after the switch is closed?
A: Steady and directed to the left
B: Steady and directed to the right
C: Short lived and directed to the left
D: Short lived and directed to the right

I think there was a diagram with this. Otherwise, how do we know which is left or right in this question?

The current in the second coil (Q) will only flow while the current (and field) in the first coil is changing.
So it only happens briefly when you actually close the switch.
This means it has to be answer C or D.
As for whether the force produced is to the left or right - it's impossible to say without a diagram and knowing if the 2nd coil is on the left or right of the first.

The diagram can help in understanding what Stonebridge explained.

Spoiler

Original post by pauline222
Can anyone provide any guidance on this multiple choice question? I am very confused.

A coil P is connected to a cell and a switch. A closed coil Q is parallel to P and is arranged on the same axis. Which describes the force acting on Q after the switch is closed?
A: Steady and directed to the left
B: Steady and directed to the right
C: Short lived and directed to the left
D: Short lived and directed to the right
Original post by Stonebridge
I think there was a diagram with this. Otherwise, how do we know which is left or right in this question?

The current in the second coil (Q) will only flow while the current (and field) in the first coil is changing.
So it only happens briefly when you actually close the switch.
This means it has to be answer C or D.
As for whether the force produced is to the left or right - it's impossible to say without a diagram and knowing if the 2nd coil is on the left or right of the first.

Sorry to resurrect this old thread, but here is the diagram. The answer is D, could you explain why?
Original post by lindahasacat
Sorry to resurrect this old thread, but here is the diagram. The answer is D, could you explain why?

I understand you request an explanation, why not you try to explain yourself by going through the following questions:
1. How would the current flow when the switch is closed in P?
The current in the loop P goes from zero to some constant value in a short time. During this short time, the magnetic field caused by the current in loop P increase in the region of the loop Q.
2. During the buildup of the magnetic field, apply Faraday’s law and Lenz’s law to deduce the direction of current in loop Q.
Recall that you have learnt in GCSE that
- like currents attract
- unlike currents repel
as shown in the diagram below.

3. Apply the concept shown in the above diagram to the current loop P and Q and answer the question.