# Question about two circular concentric coils

• phys62
In summary, the question asks for the necessary magnitude of current in the outer coil in order to cancel out the magnetic field at the common center of two concentric circular coils. The inner coil has 110 turns, a radius of 0.010 m, and a current of 5.6 A. The outer coil has 190 turns and a radius of 0.014 m. The equation B=(constant)IN/2R can be used to solve for the magnitude of the field from the first coil. From there, the opposing current in the outer coil can be calculated using the same equation and solving for the unknown current. Keeping the variables as unknowns and plugging in the given values at the end can make the
phys62

## Homework Statement

Two circular coils are concentric and lie in the same plane. The inner coil contains 110 turns of wire, has a radius of 0.010 m, and carries a current of 5.6 A. The outer coil contains 190 turns and has a radius of 0.014 m. What must be the magnitude of the current in the outer coil, such that the net magnetic field at the common center of the two coils is zero?

## Homework Equations

B=(constant)IN/2R

## The Attempt at a Solution

Ok so I have I1=5.6 A
R1=.010 m
N1=110
R2=.014 m
N2=190
I2=?

I think that I have to use that equation somehow and set them equal to each other, but I'm lost after that. Perhaps I'm using the wrong equation entirely? Any help is much appreciated!

Edit: Do I just solve for B1 and then set that equal to the equation for the 2nd coil (only make it negative)?

You should be able to figure the magnitude of the field from the first coil from what you're given.

Then they want to know what opposing current using the parameters of the other coil is needed to null out the B field at the center.

I find it easiest to keep it as variables of the 2 loops and then plug in the numbers at the end to solve for the one that you need.

Yes, you are on the right track. Since the two coils are concentric and in the same plane, the net magnetic field at the common center will be the sum of the magnetic fields produced by each coil. The equation you mentioned, B=(constant)IN/2R, is the correct equation to use. However, you need to take into account the direction of the magnetic field produced by each coil.

For the inner coil, the magnetic field will point in the same direction as the current, which is counterclockwise when viewed from the top. So the magnetic field produced by the inner coil will be positive.

For the outer coil, the magnetic field will point in the opposite direction as the current, which is clockwise when viewed from the top. So the magnetic field produced by the outer coil will be negative.

To find the net magnetic field at the common center, you can set the two equations for B1 and B2 equal to each other, since the net magnetic field must be zero. This will give you the magnitude of the current in the outer coil, which you can solve for.

Hope this helps!

## 1. What is the purpose of using two circular concentric coils?

The purpose of using two circular concentric coils is to create a magnetic field that is stronger and more uniform than what a single coil can produce. This is helpful in experiments and research that require precise and consistent magnetic fields.

## 2. How do the two coils affect each other?

The two circular concentric coils affect each other through electromagnetic induction. When an electric current flows through one coil, it creates a magnetic field that in turn induces a current in the other coil. This phenomenon allows for the transfer of energy between the coils.

## 3. Can the coils be of different sizes?

Yes, the two circular concentric coils can be of different sizes as long as they are concentric, meaning they share the same center point. However, the larger coil will have a greater influence on the smaller coil due to its larger surface area and stronger magnetic field.

## 4. What experiments can be done with two circular concentric coils?

There are various experiments that can be done with two circular concentric coils. Some common ones include studying electromagnetic induction, investigating the behavior of magnetic fields, and measuring the strength of a magnetic field at different distances from the coils.

## 5. How are the coils connected to a power source?

The coils are typically connected to a power source, such as a battery or power supply, through wires that are wound around the coils. The direction of the current flow through the coils can also be controlled to change the direction of the magnetic field produced.

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