Magnetic Fields and Electromagnetism A Level Physics

Magnetic Fields and Electromagnetism

​By Muhammad Arief Kurniawan
Mutiara Harapan Islamic School

Producing magnetic Field

1. using a permanent magnet

2. using the movement of electric charges

• The magnetic field lines come out of north poles and go into south poles.

• The direction of a field line at any point in the field shows the direction of the force that a 'free' magnetic north pole would experience at that point.

• the field is strongest where the field lines are closest together

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Representing magnetic fields

So What is electromagnet?

Basically, we are using electric source (e.g battery) to produce electric current via coil to produce magnetic field. every "field" will forced something to move (either repel or attract).

​Why coil?

​Because coil concentrates the magnetic field. one end become north pole, another end become south pole.


this type of coil called SOLENOID

Direction of Field

​The right-hand grip rule

Open Ended

State which of the pairs of electromagnets shown here attract one another, and which repel.

Magnetic Force

1. A current-carrying wire is surrounded by magnetic field.

2. this magnetic field will interact with external magnetic field.

3. so giving rise to the force on the conductor (rod).

4. the magnets give create a fairly uniform magnetic field.

5. The rod starts to roll, showing the force acting on it. To which direction?

Predict the direction of the Force

Using Fleming's Left Hand Rule
or Motor Rule

​The production of this forced called "motor effect"

Explaining the force

Match

Decide whether there is a force, and which direction

no force

yes there is force into the page

yes there is force gdown

• no force

• yes there is force into the page

• yes there is force gdown

Magnetic Flux Density

Fill in the Blanks

The unit of Magnetic flux density is Tesla (T). Please elaborate the unit of Tesla

Open Ended

a wire of length 50 cm carrying a current lies at right angles to a magnetic field of flux density 5.0 mT.

a. If 10^18 electron pass a point in the wire each second, what current is flowing? (you have to know the charge of 1 e)

b. What force acts on the wire?

Measuring Magnetic Flux Density

Measuring B Using Hall Probe

​A Hall Probe must be held so that the field lines are passing directly through it, at right angles to the flat surface of the probe.

​Measuring B with a current balance

There are two ways to measure the Force.

1. Using a balance to measure the force acting on the wire

2. Using a pivot to measure the motion of the wire

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Using a balance

red line is the wire.

when the battery is on, the current flow to the wire.

When the current flow, the force will made the wire pushed up.

Following Newton Third Law, the magnet will be pushed down at the same time.

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↓

​We can predict the force acting on the wire by calculate the weight written on the balance

Using pivots

This consists a wire frame that is balanced on two pivots.

when a current flows through the frame, magnetic field push the frame downward or upward according to the direction of the force.

we can balanced the frame using small weighs.

Current crossing fields

​Remember! There is no force if the current and magnetic field direction is parallel.

Their direction must be at right angles to produce force at max.

So What if the angle is not at right angle?

Chill! You still can predict the force. but remember I warned you. The force will be not at max.

Forces between currents

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Thank you❤️
@tsitegar