# Why wouldn't rotating the handle 90 degrees induce an EMF?

• bajerrrr
In summary, the question is asking which action would not be able to light the lightbulb by changing the magnetic field. The choices are rotating the insulating handle 90 degrees, increasing or decreasing the resistance of the variable resistor, and moving the insulating handle towards or away from the current carrying coil. The correct answer is rotating the handle 90 degrees, as it only changes the area exposed to the magnetic field. The other choices would affect the strength of the magnetic field, which could potentially light the lightbulb. It is unclear whether the rotation and movement of the handle are around a vertical axis, which would have no effect on the magnetic field. Further clarification is needed to determine the exact answer.

## Homework Statement

There is some current in the bottom coil.
The question asks which would not be able to light the lightbulb
- rotating the insulating handle 90 degrees
- increasing resistance of variable resistor
-reducing resistance of variable resistor
- moving the insulating handle towards and away from the current carrying coil.

## Homework Equations

emf = change in magnetic flux over time.
right hand rule for current carrying wire
B = (permeability of free space * current)/ (2pi * radius)
magnetic flux = BA

## The Attempt at a Solution

Rotating the handle 90 degrees would change the area exposed to the magnetic field. All the other choices would change the strength of the magnetic field. Wouldn't all of these choices be able to light the lightbulb?

#### Attachments

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bajerrrr said:
Rotating the handle 90 degrees would change the area exposed to the magnetic field.
Perhaps they meant rotating the handle about a "vertical" axis, keeping the loop in the same plane.

Not clear:
1. Rotating the insulating handle which way? Around which axis? If you rotate the handle by 90 degrees about a vertical axi through the center of the coils, then nothing happens.
2. Moving the insulating handle towards and away from... Again, which way?

Thank you for the help, I did not consider the vertical axis.

## 1. Why is rotation necessary to induce an EMF?

Rotation is necessary to induce an EMF because it causes a change in the magnetic field around a wire, which in turn creates an electric field. This electric field then produces an EMF, or electromotive force, which can generate a current.

## 2. How does rotating the handle 90 degrees affect the magnetic field?

Rotating the handle 90 degrees changes the orientation of the magnetic field lines passing through the wire. This change in orientation creates a change in the magnetic flux, which in turn induces an EMF in the wire.

## 3. Can an EMF be induced without rotation?

Yes, an EMF can be induced without rotation if there is a change in the magnetic field, such as a moving magnet near a wire or a changing current in a nearby wire. However, rotation is a common and efficient way to induce an EMF in electrical generators.

## 4. What factors affect the strength of the induced EMF?

The strength of the induced EMF depends on the speed of rotation, the strength of the magnetic field, and the angle of rotation. A faster rotation speed, stronger magnetic field, and larger angle of rotation will result in a stronger induced EMF.

## 5. How is the induced EMF related to Faraday's law of induction?

Faraday's law of induction states that the induced EMF is proportional to the rate of change of magnetic flux. This means that the more the magnetic field changes, the stronger the induced EMF will be. Rotating the handle 90 degrees is an example of changing the magnetic field, therefore it will induce an EMF according to Faraday's law.