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8.2 Force in Electromagnet

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Observation

When the power supply is switched on , the short copper wire moves to the “LEFT”

Explanation

When the switch is on, the current flows through short copper wire produced magnetic field.

The interaction between the magnetic field produced by the current and magnetic field of the permanent magnet occurred.

The interaction between the two magnetic fields produces a force on the conductor.

The method of determine the direction of the force by using Fleming’s Left-Hand Rule.

Fleming’s Left-hand Rule.

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Fleming’s Left-hand Rule states” If the thumb, first finger (forefinger)and second finger of the left hand are held at right angles to each other, then if the first finger (forefinger)represents the direction of the magnetic field and the second represents the direction of the current, then the thumb will represents the direction of the motion”

Catapult Field ( Resultant field)

Catapult field are the combinations field between

(a) the magnetic field produced by the current and magnetic field of the permanent magnet occurred.

Or

(b) the magnetic field produced by two current –carrying conductors are placed close to each other.

Catapult field type 1

Same direction – the two fields add to produce a stronger field.

Opposite direction – the two field cancel each other caused the combined field is weaker.

The direction of the catapult force is determined by Fleming’s Left-hand Rule.

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(ii)

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Catapult field type 2

(i) If the currents in the same direction, the magnetic field in the region between the two wires are in opposite directions. The two conductors attract each other.

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(ii) If the currents in the opposite directions, the magnetic field in the region between the two wires are in the same direction . The two conductors repel each other.

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Factors that affect the magnitude of the force on a current-carrying conductor in a magnitude field

1. The strength of the magnetic field.

When the strength of the magnetic field is increased ,the force acting on the conductor increases.

To increase the strength of the magnetic field by using more powerful magnet or by placing the magnets closer to each other to narrow the gap between the poles of the magnet.

2. The magnitude of the current .

When the magnitude of the current is increased, the force acting on the conductor increases.

To increase the magnitude of the current is by using a thicker wire of the same length, using a shorter wire or increasing the e.m.f of the power supply.

The experiment to investigate the relationship between the magnitude of the force on a current-carrying conductor in a magnitude field with the magnitude of the current.

Hypothesis:

The force on a current-carrying conductor in a magnitude field increases as the magnitude of the current increases.

Aim of the experiment :

To investigate the relationship between the magnitude of the force on a current-carrying conductor in a magnitude field with the magnitude of the current.

Variables in the experiment:

Manipulated variable: with the magnitude of the current.

Responding variable: the magnitude of the force on a current-carrying conductor in a magnitude field

Fixed variable: The strength of magnetic field and length of the current-carrying conductor.

List of apparatus and materials:

Magnadur magnets , U-shaped iron yoke , thick copper wire , short cooper wire and d.c supply and ruler.

Arrangement of the apparatus:

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The procedure of the experiment which include the method of controlling the manipulated variable and the method of measuring the responding variable.

The voltage of the d.c. power supply used is recorded = V

The d.c. power supply is switched on.

The distance of short copper wire moves on the thick copper wire is measured by a ruler = L

The experiment is repeated 5 times for with different voltage of the d.c. power supply.

Tabulate the data:

V

           

L

           

Analysis the data:

Plot the graph L against V

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The Turning Effect of a Current-carrying Coil in a Magnetic Field.

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When a coil carries a current in a magnetic field, the two sides of the coil perpendicular to the field experience forces in opposite directions (by using Fleming’s left-hand rule).

The pair of forces with equal magnitude but acting in opposite directions produce a turning effect.

The applications of the force on a current-carrying conductor in a magnetic field

1. Moving coil ammeter

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When a current passes through the coil, the magnetic field around it is produced.

The interaction between the magnetic field and the permanent magnet produced resultant field and two forces are in opposite directions.

The forces produce the turning effect on the coil.

The coil rotates until it stopped by the spring.

The pointer fixed to the coil deflects to show a reading on the scale.

2. Electric d.c. motor

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When a current passes through the coil, the magnetic field around it is produced.

The interaction between the magnetic field and the permanent magnet produced resultant field and two forces are in opposite directions.

The forces produce the turning effect on the coil.

The carbon brushes are pushed against the commutator. The commutator exchange contact with the carbon brushes every half rotation. This reverses the direction of the current in the coil to ensure that the forces on the coil turn the coil in one direction only.

3. Electric a.c. motor

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When a current passes through the coil, the magnetic field around it is produced.

The interaction between the magnetic field and the permanent magnet produced resultant field and two forces are in opposite directions.

The forces produce the turning effect on the coil.

The carbon brushes are pushed against the two slip rings.

In the synchronous a.c. motor , the polarity of magnet changes at the same frequency as the alternating current.

3. Moving coil loudspeaker

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When a current passes through the coil, the magnetic field around it is produced.

The interaction between the magnetic field and the cylindrical magnet produced resultant field and produces a force on the paper cone.

The force acts on the coil to move the paper cone outwards and inwards because the flowing of alternating current.

The paper cone vibrates at the frequency of the alternating current which has the same frequency as the original sound.

The air in front of the cone vibrates to produce the original sound.

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