Chapter 3: Electromagnetism
3.1 Analys Analysing ing the Magneti Magneticc Effec Effectt of of a Current-carr in Conductor By Ms Ms Nurul Ain Mat Aron
Objectives 1. State what an an el electromagnet is. 2. Draw Draw the the mag magne netic tic field field patte pattern rn due due to to a curr curren entt in in a: straight wire coil Solenoid 3. Plan Plan and and con condu duct ct expe experi rime ment ntss to to stu study dy fa fact ctor orss tha thatt affect the strength of the magnetic field of an electromagnet. 4. Desc escribe ribe appl applic icaation tionss of of ele electro ctrom magne agnets ts..
Introduction to Magnetism (Revision)
Magnetic materials (Ferromagnetic Material)
Magnet
Introduction to Magnetism (Revision) Magnet
Magnetic Field
a magnet has 2 poles
Magnetic Field – a region in the surrounding of a magnet which a magnetic material experiences a detectable force
Introduction to Magnetism (Revision)
Magnetic field the magnetic field is represented by the magnetic field lines
Magnetic Field Pattern •
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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 Maxwell’s Screw Rule
Magnetic Field Pattern – Straight Wire
Magnetic Field Pattern – Straight Wire
Magnetic Field Pattern – Straight Wire
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
Magnetic Field Pattern – Circular Coil
Plan view
Magnetic Field Pattern – Solenoid A solenoid is a long coil made up of a numbers of turns of wire
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.
Magnetic Field Pattern – Solenoid Determining 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.
Magnetic Field Pattern – Solenoid Determining 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.
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
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
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.
Electromagnetism •
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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.
What is an electromagnet? •
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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.
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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.
Describe Applications Of Electromagnets (Electric Bell)
Describe Applications Of Electromagnets (Electric Bell - Explanation) 1. 2.
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When the switch is on, the circuit is completed and current flows. The electromagnet becomes magnetised and hence attracts the softiron armature and at the same time pull the hammer to strike the gong. This enables the hammer to strike the gong. 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. When the circuit is connected, the electromagnet regain its magnetism and pull the armature and hence the hammer to strike the gong again. This cycle repeats and the bell rings continuously.
Describe Applications Of Electromagnets (Electromagnetic Relay)
A relay is an electrical switch that opens and closes under the control of another electrical circuit.
Describe Applications Of Electromagnets (Electromagnetic Relay - Explanation) 1. 2.
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The switch is operated by an electromagnet to open or close one or many sets of contacts. 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. When the switch is close, the electromagnet is magnetised and attracts one end of the iron armature. The armature is then closes the contacts (2nd switch) and allows current flows in the second circuit. When the 1st switch is open again, the current to the electromagnet is cut, the electromagnet loses its magnetism and the 2nd switch is opened. Thus current stop to flow in the 2nd circuit.
Describe Applications Of Electromagnets (A Telephone Earpiece)
Describe Applications Of Electromagnets (A Telephone Earpiece - Explanation) 1. 2. 3. 4. 5. 6. 7.
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An electromagnet is used in the earpiece of a telephone. When you speak to a friend through the telephone, your sound will be converted into electric current by the mouthpiece of the telephone. The current produced is a varying current and the frequency of the current will be the same as the frequency of your sound. The current will be sent to the earpiece of the telephone of your friend. When the current passes through the solenoid, the iron core is magnetised. The strength of the magnetic field changes according to the varying current. When the current is high, the magnetic field will become stronger and when the current is low, the magnetic field become weaker. The soft-iron diaphragm is pulled by the electromagnet and vibrates at the frequency of the varying current. The air around the diaphragm is stretched and compressed and produces sound wave. The frequency of the sound produced in the telephone earpiece will be the same as your sound.
Describe Applications Of Electromagnets (A Circuit Beaker)
Describe Applications Of Electromagnets (A Circuit Beaker - Explanation) 1. 2.
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A circuit breaker is an automatic switch that cut off current in a circuit when the current become too large. When the current in a circuit increases, the strength of the electromagnet will increase in accordance; this will pull the soft iron armature towards the electroma net. As a result, the spring pulls apart the contact and disconnects the circuit immediately, and the current stop to flow. 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.
