P7 - Magnetism And Electromagnetism Flashcards
Poles of a magnet (3)
- Are the places where the magnetic forces are strongest
- When the two poles are brought close together they exert a force on each other
- To like poles repel each other and two unlike poles attract each other - attraction and repulsion are examples of non-contact forces
What is a Permanent magnet
Produces its own magnetic field
What is an Induced magnet
Is a material that becomes a magnet when it is placed in a magnetic field
induced magnetism
Induced magnetism always causes a force attraction - when removed from the magnetic field an induced magnet loses most/all of its magnetism quickly
Magnetic field
Is the region around a magnet where a force acts on another magnet or on a magnetic material (iron, steel, cobalt and nickel)
What is the force between a magnet and magnetic material
Is always a force of attraction
What does the strength of the magnetic field depend on
The distance from the magnet - the field is stronger at the poles of the magnet
Direction of the magnetic field at any point (2)
- Is given by the direction of the force that would act on another north pole placed at that point
- the direction of magnetic field line is from the north (seeking) pole of a magnet to the south (seeking) pole of the magnet
Magnetic compasses (2)
- Contain a small bar magnet
* The compass needle points in the direction of the Earth’s magnetic field
How to plot the magnetic field of a magnet using a compass
Move compass around a magnet and trace its position on some paper to build up a picture of what the magnetic field looks like
Draw Magnet field pattern of a bar magnet
Check photos
How is the behaviour of a magnetic compass related to evidence that the core of the Earth must be magnetic
When magnetic compasses are not near a magnet compasses always point north - due to the Earth generating its own magnetic field which shows the core of the earth must be magnetic
What happens when a current flows through a conducting wire
A magnetic field is produced around the wire - the strength of the magnetic field depends on the current through the wire and the distance from the wire
Shaping of a wire to form a solenoid
Increases the strength of the magnetic field created by a current through the wire - the magnetic field inside a solenoid is strong and uniform
Magnetic field around a solenoid (2)
- Has a similar shape to that of a bar magnet
* Adding an iron core increases the strength of the magnetic field of a solenoid
Electromagnet
Is a solenoid with an iron core
Describe how the magnetic effect of a current can be demonstrated (right-hand thumb rule) (2)
• Using tour right hand, point your thumb in the direction of a current and curl your fingers
• The direction of your fingers is the direction of the field
(Check photos)
Draw magnetic field pattern for a straight wire carrying current
(Check photos)
Draw magnetic field pattern for a solenoid
Check photos
Motor effect
Is when a conductor carrying a current is placed in a magnetic field the magnet producing the field and the conductor, exert a force on each other
What does Fleming’s left-hand rule represent (3)
- The relative orientation of the force
- The current in the conductor
- The magnetic field
Factors that affect the size of the force on the conductor (3)
- Magnetic flux density
- Size of current through the conductor
- The length of the conductor
Equation linking force, magnetic flux density, current and length
Force (N) = magnetic flux density (T) x current (A) x length (m)
The basis of an electric motor
A coil of wire carrying a current in a magnetic field tends to rotate
Explain how the force on a conductor in a magnetic field causes the rotation of the coil in an electric motor (5)
- Forces act on the two side arms of a coil wire thats carrying a current
- Because the coil is on a spindle and forces act one up and one down it rotates
- Split-ring commutator swaps the contacts every half turn to keep the motor rotating in the same direction
- The speed of your motor can be increased by increasing the current, adding more turns to the coil or increasing the magnetic flux density
- You can use Fleming’s left-hand rule to work out which way the coil will turn
