# Induced Current Direction in a Changing Magnetic Field

• JSapit
In summary, the problem involves a 50 turn coil with a radius of 5.7 cm and an external magnetic field decreasing from 1.8 T to 0 T in 3.3 s. The resistance of the coil is 2.8 ohm and the induced current is found to be 0.9442 A. The direction of the current is determined using Faraday's Law, which states that a changing magnetic field will induce an emf, causing a current to circulate in the coil. Therefore, the current will flow counterclockwise (CCW).
JSapit

## Homework Statement

The component of the external magnetic field along the central axis of a 50 turn coil of radius 5.7 cm decreases from 1.8 T to 0 T in 3.3 s.

(a) If the resistance of the coil is 2.8 ohm, what is the magnitude of the induced current in the coil?

(b) What is the direction of the current if the axial component of the field points towards the viewer?

1. CCW
2. CW

## Homework Equations

EMF=-(phi)/(time)

Phi=BASin(theta)

## The Attempt at a Solution

I found the current using -N(B/t)*A

I found it to be 0.9442 A.

Now I'm just not sure on part B.

Last edited:
Well, there won't be any current unless the B is changing!
"A changing B causes an E to circulate around it."

B is changing, though. It said in the problem that "B decreases from 1.8T to 0T."

Yes, B is changing so you will get an emf in the coil, causing a current.
I meant that any formula you find for the emf MUST have a changing B.
Faraday's Law is what you are looking for.

## 1. How does changing the number of turns in a coil affect B?

Changing the number of turns in a coil affects B by directly impacting the strength of the magnetic field. More turns in a coil results in a stronger magnetic field, while fewer turns results in a weaker magnetic field.

## 2. What happens to B when the current through a coil is changed?

When the current through a coil is changed, B is also changed. This is because B is directly proportional to the current, meaning that as the current increases, so does the strength of the magnetic field.

## 3. How does the shape of a coil impact B?

The shape of a coil can impact B by affecting the direction and distribution of the magnetic field lines. A solenoid coil, for example, has a more concentrated and uniform magnetic field compared to a flat coil.

## 4. What other factors besides the number of turns and current can influence B in a coil?

Other factors that can influence B in a coil include the material of the coil, the diameter of the coil, and the distance between the coil and the magnetic material. These factors can affect the strength and direction of the magnetic field.

## 5. How does changing the direction of the current through a coil affect B?

Changing the direction of the current through a coil can change the direction of the magnetic field. If the current is reversed, the magnetic field will also reverse. This is known as the right-hand rule, where the thumb points in the direction of the current and the fingers curl in the direction of the magnetic field.

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