P4.2 Uses Of Magnetism Flashcards

1
Q

Motor effect

A

2 magnets exerting a force upon each other

When there is a current in the coil, the sides of the coil experiences a force in opposite directions, allowing the current to produce a magnetic field
Split ring commutator ensures that the coil rotates in same direction by reversing the current every half turn
Here the two halves of the commutator swap from one carbon brush to the other
Without a split ring commutator, the coil would change direction every half turn and not rotate in one continuous direction

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2
Q

What is generated around a current carrying wire

A

Magnetic field

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3
Q

Gravitational field strength (g)

A

Measured in newtons per kg (N/kg)
10N/kg on Earth

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4
Q

Magnetic field strength / magnetic flux density

A

Symbol: B
Unit: Tesla (T)

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5
Q

Fields, currents, forces all have what

A

Directions (left right up down)

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6
Q

Symbol for something going into the page
(Diagram used in showing direction of current in a wire)

A

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7
Q

Symbol for something coming out of the page
(Diagram used in showing direction of current in a wire)

A

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8
Q

Motor effect - size of force equation

A

F = BIL

F = force on conductor: Newtons
B = magnetic flux density: Tesla
I = current: Amps
L = length of conductor in field: Meters

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9
Q

Fleming’s left hand rule

A

Used to calculate the force on the wire

Finger 1: field : point forward
Finger 2: current: point down
Thumb: movement: point right

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10
Q

What happens when fields of 2 wires interact

A

They both experience a force
Attract if current flow in same direction
Repel if they flow in opposite directions

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11
Q

Electric motor (simple)

A

Uses motor effect to transfer electrical energy to kinetic energy
Consists of a loop/length of wire with a current in a magnetic field
Motor rotates as the current in the loop of wire flows in opposite directions in the opposite sides of coil, forces act in opposite directions on opposite sides of the coil, causing the coil to rotate

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12
Q

Electric motor (complex)

A

North ( \o/ )South
. v ^
. L_ı|⅃
1) The left part of this coil is pushed upwards and the right half downwards. (Check with Fleming’s left-hand rule.)
2) No current, but the coil continues to turn because of its own momentum
3) The direction of the current in the coil and commutator is reversed. Now the blue part is pushed downwards and the red half upwards
Split ring commutator ensures that the motor rotates in the same direction

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13
Q

Split ring commutator

A

Reverses direction of current in the coil of the motor every half turn
Keeps the coil turning the same direction

Split ring commutator diagram:
Coil wire
\ \
|| ||
—▪️( * )▪️— *gaps
\ \
Contact to DC power supply

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14
Q

Increase speed of motor

A

Increase size of force acting F=BIL:

Increase current in coil
Increase strength of magnetic field/magnets
Have more loops/longer wire

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15
Q

Catapult field diagram for motor coil

A

|S N|————>————|S N|
| | ‾‾———>———__ | |
| | ‾‾———>———__ | |
| | \ / ‾ ‾ \ | |
| | \ \ ^ / / ‾‾ | |
| | \ \ | / / | |
| | \ \v(⊙) / / ^(⨂) | |
| | - . ->- . - | | |
| | - . > . - v | |
| | ‾‾———>———__ | |
| | ‾‾———>———__ | |
|S N|————>————|S N|

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16
Q

Why some motors would use electromagnets instead of permanent magnets

A

Produce stronger magnetic fields,
which produces larger force

17
Q

Why bigger motors produce a larger force on the coil

A

Longer length of coil (loops) in a stronger magnetic field

18
Q

Type of current needed for motors

A

Alternating current

19
Q

How does an alternating current generator work

A

For current to be generated, motion, magnets and wires are needed
Magnets provide a magnetic field
Motion is supplied when the coil is manually rotated
Brushes make contact between the split ring commutator and the circuit and ensures that current continuously flows in circuit