The Motor Effect (7.2) Flashcards
What happen when a current flows through a conducting wire?
a magnetic field is produced around the wire
2 things
What does the strength of the magnetic field depend on?
the current through the wire and the distance from the wire
Shaping a wire to form a solenoid (coils of wire) does what?
increases the strength of the magnetic field created by a current through the wire
How would you describe the magnetic field inside a solenoid?
strong and uniform
The magnetic field around a solenoid has a similar shape to that of a (…)
bar magnet
What is an electromagnet?
a solenoid with an iron core
Adding an iron core to a solenoid, creating an electromagnet, does what?
increases the strength of the magnetic field of a solenoid
How can the magnetic effect of a current can be demonstrated?
Put a piece of wire that is free to move in a magnetic field, then put a current through it
It will move as current flows through it
Draw the magnetic field pattern for a straight wire carrying a current with its direction upwards (showing the direction of the field)
this is the right hand grip rule - learn it
Draw the magnetic field pattern for a solenoid (showing the direction of the field)
Magnetic fields travel from the (…) pole to (…) pole
north to south
also know what will happen if two like poles are close
3 ways
How can you make an electromagnet stronger?
- wrapping the coil around an iron core
- adding more turns to the coil
- increasing the current flowing through the coil
The photo shows a relay circuit, describe how it works
When the switch is closed, current is induced and flows and the iron rocker arm is attracted to the electromagnet.
The arm rotates about the central pivot and pushes the contacts together.
Current now flows through circuit 2, which is now switched on and the motor turns
circuit two may have a large current flowing through it - dangerous to person
What is the motor effect?
When a conductor carrying a current is placed in a magnetic field, the magnet producing the field and the conductor (which induces its own magentic field) exert a force on each other
fields interact
3 things
What does Fleming’s left-hand rule represent?
- the relative orientation of the force
- the current in the conductor
- the magnetic field
Present Fleming’s left hand rule. It should look like this…
at right angles to eachother
acronym: FBI
In which direction will this wire feel a force?
With forefinger (magnetic field) pointing left to right, and second finger (current) pointing down, your left thumb (force) will point towards you
3 things
What are the factors that affect the size of the force on the conductor?
- the current in the wire increases
- the strength of the magnetic field increases
- length of wire in magnetic field
F = BIL
A coil of wire carrying a current in a magnetic field tends to (…)
rotate
What is a dc motor?
An electrical device that uses direct current to produce a turning effect.
What type of motor is an electric motor?
a dc motor
4 marks
Describe how an electric motor works?
The sides of the coil (parallel to the magnet) experience a force (in opposite directions)
allow the magnetic fields interact causing the coil to rotate
(each half-turn) the two halves of the (rotating) commutator swap from one brush to the other
(each half-turn) the commutator reverses the current (in the coil)
Loudspeakers and headphones do what?
to convert variations in current in electrical circuits to the pressure variations in sound waves
Describe how moving-coil loudspeaker and headphones work
- Current creates a magnetic field (around the coil)
- Which interacts with the permanent magnetic field
- Producing a (resultant) force (causing the coil/cone to move)
- When the direction of current reverses, the direction of the (resultant) force reverses to the opposite direction (producing pressure variations in sound wave)
