7.2 The motor effect
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What is produced when current flows through a conducting wire?
A magnetic field is produced around the wire
What determines the strength of the magnetic field around a current-carrying wire?
The magnitude of current flowing through the wire and the distance from the wire
What is a solenoid?
A coil of wire which when current passes through creates a strong magnetic field
Describe the magnetic field found inside a solenoid
Strong and uniform
What is an electromagnet?
A solenoid with an added iron core. Adding the iron core increases the strength of the magnetic field.
What is the motor effect? (Higher)
When a force is exerted between a magnetic field and and a current-carrying conductor placed inside that field
What rule is used to determine the force experienced due to the motor effect? (Higher)
Fleming’s left-hand rule
When using Fleming’s left-hand rule, what does the index finger represent? (Higher)
The index finger points in the direction of the magnetic field
When using Fleming’s left-hand rule, what does the middle finger represent? (Higher)
The middle finger points in the direction of current flow in the conductor
What factors affect the size of the force on a current-carrying wire in a magnetic field? (Higher)
The magnitude of the current flowing through the conductor The strength of the magnetic field that the conductor is placed in
If the direction of current in a current-carrying wire placed in a uniform magnetic field is reversed, what happens to the force? (Higher)
The direction of the force is reversed
If the strength of the current in a current-carrying wire placed in a uniform magnetic field is increased, what happens to the force? (Higher)
The strength of the force is increased
What is the unit used for magnetic flux density? (Higher)
Tesla (T)
What criteria must be met for the equation linking force, magnetic flux density, current and length to hold? (Higher)
The conductor must be at right-angles to the magnetic field it is placed in
How does an electric motor work? (Higher)
A coil of wire, carrying a current, is placed in a magnetic field. The forces on the two sides perpendicular to the field experience forces in opposite directions which causes a rotational effect.
How do loudspeakers make use of the motor effect? (Higher)
The motor effect is used to convert variations in the current of an electrical circuit into the pressure variations which produce audible sound
Explain how a loudspeaker works. (Higher)
A cone with a wire wrapped around it is connected to an AC power supply and is placed in a magnetic field. When current flows through the wire, it produces a second magnetic field, which interacts with the permanent magnetic field. This produces a force which causes the cone to vibrate.
How is the pitch of the sound from a loudspeaker changed? (Higher)
The frequency of the AC current is altered. This creates a different frequency of vibration in the cone.