topic 7: magnetism and elctromagnetism Flashcards
At which part of a magnet are the magnetic forces strongest
The poles of the magnet
What happens when two magnets are brought close to each other?
They exert a force on each other
what type of force is exerted? If two like poles of a magnet are brought near each other?
a repulsive,no contact force
What type of force is exerted if two unlike poles of a magnet of brought each other?
an attractive ,noncontact force
What is the difference between a permanent magnet and an induced magnet?
A permanent magnet produces its own magnetic field
An induce magnet becomes magnetic when placed in a magnetic field
what type of force does induced magnetism always cause
A force of attraction
what happens when an induced magnet is removed from a magnetic field?
The induced magnet loses most/all of its magnetism
what is a magnet field?
The region surrounding a magnet where another magnet or magnetic material experiences a noncontact force
give four examples of magnetic materials
Iron
Steel
Cobalt
Nickel
what can always be said about the force between a magnet and a magnetic material
It is always attractive
how does the strength of a magnetic field alter as you move further away from the magnet producing it?
The magnetic field strength decreases the further you move away
in what direction does a magnetic field point?
In the direction that a North Pole would experience a force if placed in the field
From the north seeking pole to the south seeking pole of a magnet
What does a magnetic compass contain?
A small bar magnet that points in the direction of the earth magnetic field
what is produced when the 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 the current flowing through the wire
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?
When a force is exerted between a magnetic field and current carrying conductor placed in that field
what rule is used to determine the force experience due to the motor effect
Flemming’s left hand rule
when using Flemming‘s left-hand rule, what does the forfinger represent?
The forfinger points in the direction of the magnetic field
when using Flemming’s left hand rule what does the second finger represent?
The second 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?
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 a current in a current carrying wire placed in a uniform magnetic field is reversed, what happens to the force?
 the direction of the forces is reversed
If the strength of the current in a current carrying wire are placed in a uniform magnetic field is increased, what happens to the force
The strength of the force is increased
what criterion must be met for the equation linking force, magnetic flux density, current to length to hold
The conductor must be right angles to the magnetic field it is placed in
what is the unit used for magnetic flux density?
Tesla, T
How does an electric motor work?
A coil of wire, carrying a current, is placed in a magnetic field
The forces on the two sides perpendicular to the field experiences forces in opposite direction
This causes a rotational effect
How do loudspeakers make use of the motor effect?
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 loudspeakers work
A cone with a wire wrapped around it is connected to an AC power supply and is placed in a permanent magnetic field
When a current flows through the wire, it creates a second magnetic field, which interacts with the permanent field
This producers a force which causes the cone to vibrate
How is the pitch of the sound from a loudspeaker changed?
The frequency of the AC current is altered
This creates a different frequency of vibration in the cone
what happens when an electrical conductor moves relative to a magnetic field?
A potential difference is induced across the ends of the conductor
What happens to an electrical conductor when there is a change to the magnetic field that it is placed in?
A potential difference is induced across the ends of the conductor
What is the requirement for an induced potential difference to cause a current flow?
The conductor must form a close loop or be part of a complete circuit
What can be said about the direction of the magnetic field produced by an induced current?
The direction of the field is such that it opposes the change that induced the current
This change is either the movement of a conductor or a change to the field
What are two ways that the generator effect is used to generate different types of current?
in an alternator to produce alternating current
In a dynamo to produce Direct current
What electromagnetic effect does a microphone take advantage of and how?
The generator effect
It converts the pressure variations in soundwaves into an alternating current in a circuit
Describe the makeup of a basic transformer
A primary coil and a secondary coil of wire wrapped round an iron cone
why is iron used as the core for a transformer?
 it is easily magnetised
explain how a transformer works
An alternating current flows through the primary coil
This induces a changing magnetic field in the core
this changing magnetic induces a current to flow in the secondary coil
Why must the current flowing through the primary coil of a transformer be alternating?
for current to be induced in the secondary coil, the magnetic field in the core must be continuously changing
For the magnetic field to be changing, the current in the primary coil must be alternating
what can be said about the electrical power input and output of an 100% efficient transformer?
The electrical power input is equal to the electrical power output
