Post on 03-Jun-2018
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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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Introduction to Magnetism
(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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Introduction to Magnetism
(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 Straight Wire
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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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Factors That Affect The Strength Of The
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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Factors That Affect The Strength Of The
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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Describe Applications Of Electromagnets
(Electromagnetic Relay)
A relay is an electrical switch that opens and closes under the control of another
electrical circuit.
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Describe Applications Of Electromagnets
(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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Describe Applications Of Electromagnets
(A Telephone Earpiece)
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Describe Applications Of Electromagnets
(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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Describe Applications Of Electromagnets
(A Circuit Beaker)
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Describe Applications Of Electromagnets
(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.