The Motor Effect - Paper 2 Flashcards
What is the motor effect?
When a force is exerted on a current-carrying wire due to the presence of a magnetic field
Describe the motor effect
A current-carrying conductor is placed between magnetic poles and the two magnetic fields interact
One field is from the current-carrying wire
One field is from the other magnetic poles
Which hand rule is associated with the motor effect?
Fleming’s left-hand rule
Force, field, current
Give an example of a current-carrying conductor in the motor effect
A wire
At what angle does the wire have to be relative to the magnetic field to experience the full force of the motor effect?
90 degrees
Between 90 degrees and being directly along the magnetic field, only some of the force will be felt by the wire
In the motor effect, we focus on the force acting on which component?
The wire
In the motor effect, why does the wire experience a force?
The interaction of two magentic fields
One of which is its own created because it is carrying current
Which finger of Fleming’s left hand rule refers to the direction of the force on the wire/current-carrying conductor?
Thumb
Force, field, current
Which effect is Fleming’s left hand rule used for?
The motor effect
What is the equation F=BIl used for?
Determining the size of the force acting on a conductor in a magnetic field
The motor effect
F=BIl is used in relation to what effect?
The motor effect
What does each of the letters in F=BIl refer to?
F - Force
B - Magnetic Flux Density
I - Current
l - Length
Length effects force because a longer wire means there are more electrons moving within the magnetic field
What is magnetic flux density?
The strength of a magnetic field
How many flux/field lines in a region
What is the unit for magnetic flux density?
Tesla (T)
or N/Am
In which unit is length measured?
Metres (m)
What is the difference between a motor and a generator?
A motor converts electrical energy into mechanical energy whereas a generator turns mechanical energy into electrical energy
A loudspeaker would be a motor because it moves a cone back and forth by converting electrical signals into sound waves
A microphone would be a generator because it converts sound waves into electrical signals
In which type of motor would you find a split-ring commutator?
A DC motor
What is a split-ring commutator in a DC motor?
A rotary switch which reverses the direction of current flow every half turn so that the wire only rotates one direction
In which direction does current flow?
Positive to negative
This is conventional current - use this
In a DC motor, why might the coil of wire stop moving when vertical?
Because the coil is moving parallel to the magnetic field so produces no force
Think about moving the left hand rule round in a circle as the wire (direction of current) moves around
Give two features which enable the coil of wire to keep moving in a DC motor after it is vertical and it is moving parallel to the magnetic field
The momentum of the motor
A split-ring commutator to prevent it then reversing direction
