P7 Flashcards
What are each end of the magnet called
Poles
North and south
Where are magnetic feilds strongest
At the poles
What happens when we bring two magnets close together
They exert a force on eachother
Like poles repel
Unlike poles attract
Non contact forces
What is a permanent magnet
A magnet which produces its own magnetic field
Eg bar magnet
What is an induced magnet
An object that become a magnet when it is placed in a magnetic field
Always causes force of attraction
What are the magnetic materials
Iron steel cobalt nickel
What is a magnetic field
A region around a magnet where a force acts on another magnet or magnetic material
What happened if we place a magnetic material into a magnetic field
Experiences a force of attraction towards the magnet
How can we find magnetic field
Using a magnetic compass
-place compass near north pole
-draw cross at north pole of the magnet
-move the compass so the South Pole is on the cross,draw another cross at north pole
-continue until we have plotted a magnetic field line
-join crosses with straight line and draw arrow on direction
How do we know the earth has it’s own magnetic field
If we hold a compass away from any magnet then the needle always points in the north-south direction.
What happens when a current flows through a conducting wire
A magnetic field is produced around the wire
How can we increase magnetic feild strength produced by a solenoid
-increase current
-iron core
-increase turns of coils
What happenes in a solenoid if we change the direction of the current
We change the direction of the magnetic field
How can we figure out direction of current
Flemings right hand rule
Place our right hand so the thumb is in the direction of the current,now the fingers are pointing in the direction of the magnetic field
What is a solenoid containing an iron core called
Electro magnet
Why are electro magnets useful
-We can change the strength
-turn on or off
What is the motor effect?
If you bring a current carrying wire near another magnetic field, the fields interact and a force is produced
How do we calculate the size of force produced during Moter effect
F=BxIxL
Force (n)=
magnetic flux density (T) x current (A) x length (m)
How do we determine direction of force during motor effect
Flemings left hand rule
Thumb=direction of force
First finger=direction of magnetic field
Second finger= direction of current
What happens in the motor effect if the conductor is parallel to the magnetic field
It will not experience a force
How does a motor continue spinning
For a motor to continue spinning A split ring communicator is used, this swaps the contacts of the motor every half turn therefore reversing the current
When there is a current in a coil,the coil rotates continuously
Why?
-The coil in the magnetic field will experience a force when current flows
-The current will flow in opposite directions in the coil, so each side will experience in opposite force which allows it to turn
-Every half a turn, the rotating communicator swaps carbon brush, and the current is reversed
-This reverses the force, each side experiences, keeping it rotating
What does switching the direction of the current do in an electric motor?
By switching the direction of the current, the split ring communicator, allows the motor to keep rotating in the same direction
how can we use a permanent magnet to identify a permanent magnet,magnetic metal and regular metal
-permanent metal will attract magnetic material
-magnet would have no effect on regular metal
-magnet could only repel the permanent magnet
how can a electromagnet be used to move magnetic materials
-by completing the circuit the electromagnet is turned on
-there is a current in the coil which produces a magnetic field around the coil
-move electromagnet towards the blocks
-the block is attracted to the electromagnet
-switching off the current switches off the electromagnet
-releasing the block
how to find frequency
-use a stopwatch
-count the number of waves passing a point in a fixed time period
- divide the time by the number of waves to determine the time or one wave, T
-f = 1/T
how to find wavelength
-use a camera to freeze the image
-use a metre rule to measure the distance between two
wavefronts
- count the number of waves between the wavefronts
-divide distance by the number of waves to determine λ
The paper clip in Figure 2 is not a permanent magnet.
Explain what would happen if the paper clip was removed and brought close to the
south pole of the permanent magnet.
-paper clip will still experiannce a force of attracton towards the magnet
-because its become an induced magnet
