3.1 - Analysing the Magnetic Effect of a Current-carrying Conductor

8/11/2019 3.1 - Analysing the Magnetic Effect of a Current-carrying Conductor

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3.1 Analysing the Magnetic Effect of a

Current-carr in Conductor

Chapter 3: Electromagnetism

By Ms Nurul Ain Mat Aron


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Objectives

1. State what an electromagnet is.

2. Draw the magnetic field pattern due to a current ina:

straight wire

coil

Solenoid

3. Plan and conduct experiments to study factors that

affect the strength of the magnetic field of anelectromagnet.

4. Describe applications of electromagnets.


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Introduction to Magnetism

(Revision)

Magnet

Magnetic materials

(Ferromagnetic Material)


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(Revision)Magnetic FieldMagnet

Magnetic Fielda region in the surrounding of a

magnet which a magnetic material experiences a

detectable force

a magnet has 2 poles


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(Revision)

Magnetic field the magnetic field is represented by the magnetic field lines


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Magnetic Field Pattern

The direction of the magnetic field can be determined by using a

small compass. The direction pointed by the compass needle shall

be the direction of the magnetic field at that point.

The direction of the magnetic filed can also be determined by using

the Right-hand Grip Rule or Maxwells Screw Rule


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Magnetic Field Pattern Straight Wire


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Magnetic Field Pattern Circular Coil

The magnetic field of a circular coil is identical to the fields of two

straight wires, one carrying current upwards and the other downwards

In the centre of the coil, the field pattern is a straight line, while both sides

are curved


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Magnetic Field Pattern Circular Coil

Plan view


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Magnetic Field Pattern Solenoid

The field lines in the solenoid are close to each other, indicates that the

magnetic field is stronger inside the solenoid.

The field lines are parallel inside the solenoid. This shows that the strength

o e magne c e s a ou un orm ns e e so eno .

The magnetic field of a solenoid resembles that of the long bar magnet, and

it behaves as if it has a North Pole at one end and a South Pole at the other.


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Magnetic Field Pattern SolenoidDetermining the Pole of the Magnetic Field

Method 1 ( Right-hand Grip Rule)

Imagine your right-hand gripping the coil of the solenoid such that your

fingers point the same way as the current. Your thumb then points in the

direction of the field.

Since the magnetic field lines always come out from the North Pole, hence

the thumb points towards the North Pole.


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Magnetic Field Pattern SolenoidDetermining the Pole of the Magnetic Field

Method 2 - (Visualisation)

Try to visualise that you are viewing the solenoid from the 2 ends as

illustrated in figure below.

The end will be a North pole if the current is flowing in the aNticlockwise,

or a South pole if the current is flowing in the clockwiSe direction.


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Factors That Affect The Strength Of The

Magnetic Field

The strength of the magnetic field produces in a straight wire can be increased by

1. Increase the current flowing through the wire

2. Increase the number of wires carrying the current


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Magnetic Field

The strength of the magnetic field produces in a circular coil can be increased by

1. Increase the current flowing through the coil

2. Increase the number of turns in the coil


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Magnetic Field

The strength of the magnetic field produces in a solenoid can be increased by

1. Increase the current flowing through the coil

2. Increase the number of turns in the coil

3. Use a soft-iron core within the solenoid.


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Electromagnetism

When current passes through a conductor, magnetic field will be

generated around the conductor and the conductor become a magnet.

This phenomenon is called electromagnetism.


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What is an electromagnet?

Since the magnet is produced by electric current, hence it is called the

electromagnet.

An electromagnet is a type of magnet in which the magnetic field is

produced by a flow of electric current. The magnetic field disappears when

the current ceases.

current.

In short, when current flow through a conductor, magnetic field will be

generated. When the current ceases, the magnetic field disappear.

An electromagnet is a type of magnet in which the magnetic field is

produced by a flow of electric current.


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Describe Applications Of Electromagnets

(Electric Bell - Explanation)1. When the switch is on, the circuit is completed and current flows.

2. The electromagnet becomes magnetised and hence attracts the soft-

iron armature and at the same time pull the hammer to strike the

gong. This enables the hammer to strike the gong.

3. As soon as the hammer moves towards the gong, the circuit is

broken. The current stops flowing and the electromagnet loses its

magnetism. This causes the spring to pull back the armature and

reconnect the circuit again.

4. When the circuit is connected, the electromagnet regain its

magnetism and pull the armature and hence the hammer to strike thegong again.

5. This cycle repeats and the bell rings continuously.


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(Electromagnetic Relay)

A relay is an electrical switch that opens and closes under the control of another

electrical circuit.


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(Electromagnetic Relay - Explanation)1. The switch is operated by an electromagnet to open or close one or

many sets of contacts.

2. A relay has at least two circuits. One circuit can be used to control

another circuit. The 1st circuit (input circuit) supplies current to the

electromagnet.

3. When the switch is close, the electromagnet is magnetised and

attracts one end of the iron armature.

4. The armature is then closes the contacts (2nd switch) and allows

current flows in the second circuit.

5. When the 1st switch is open again, the current to the electromagnet iscut, the electromagnet loses its magnetism and the 2nd switch is

opened. Thus current stop to flow in the 2nd circuit.


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(A Telephone Earpiece)


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(A Telephone Earpiece - Explanation)1. An electromagnet is used in the earpiece of a telephone.

2. When you speak to a friend through the telephone, your sound will be

converted into electric current by the mouthpiece of the telephone.

3. The current produced is a varying current and the frequency of the current will

be the same as the frequency of your sound.

4. The current will be sent to the earpiece of the telephone of your friend.

5. When the current passes through the solenoid, the iron core is magnetised. The

strength of the magnetic field changes according to the varying current.

6. When the current is high, the magnetic field will become stronger and when

the current is low, the magnetic field become weaker.

7. The soft-iron diaphragm is pulled by the electromagnet and vibrates at thefrequency of the varying current. The air around the diaphragm is stretched

and compressed and produces sound wave.

8. The frequency of the sound produced in the telephone earpiece will be the

same as your sound.


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(A Circuit Beaker)


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(A Circuit Beaker - Explanation)1. A circuit breaker is an automatic switch that cut off current in a circuit when

the current become too large.

2. When the current in a circuit increases, the strength of the electromagnet will

increase in accordance; this will pull the soft iron armature towards theelectroma net.

3. As a result, the spring pulls apart the contact and disconnects the circuit

immediately, and the current stop to flow.

4. We can reconnect the circuit by using the reset button. The reset button can be

pushed to bring the contact back to its original position to reconnect the circuit.

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3.1 - Analysing the Magnetic Effect of a Current-carrying Conductor