P4.2 Uses Of Magnetism Flashcards
Motor effect
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
What is generated around a current carrying wire
Magnetic field
Gravitational field strength (g)
Measured in newtons per kg (N/kg)
10N/kg on Earth
Magnetic field strength / magnetic flux density
Symbol: B
Unit: Tesla (T)
Fields, currents, forces all have what
Directions (left right up down)
Symbol for something going into the page
(Diagram used in showing direction of current in a wire)
⨂
Symbol for something coming out of the page
(Diagram used in showing direction of current in a wire)
⨀
Motor effect - size of force equation
F = BIL
F = force on conductor: Newtons
B = magnetic flux density: Tesla
I = current: Amps
L = length of conductor in field: Meters
Fleming’s left hand rule
Used to calculate the force on the wire
Finger 1: field : point forward
Finger 2: current: point down
Thumb: movement: point right
What happens when fields of 2 wires interact
They both experience a force
Attract if current flow in same direction
Repel if they flow in opposite directions
Electric motor (simple)
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
Electric motor (complex)
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
Split ring commutator
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
Increase speed of motor
Increase size of force acting F=BIL:
Increase current in coil
Increase strength of magnetic field/magnets
Have more loops/longer wire
Catapult field diagram for motor coil
|S N|————>————|S N|
| | ‾‾———>———__ | |
| | ‾‾———>———__ | |
| | \ / ‾ ‾ \ | |
| | \ \ ^ / / ‾‾ | |
| | \ \ | / / | |
| | \ \v(⊙) / / ^(⨂) | |
| | - . ->- . - | | |
| | - . > . - v | |
| | ‾‾———>———__ | |
| | ‾‾———>———__ | |
|S N|————>————|S N|