P7 - Magnetism And Electromagnetism

Question 1

Poles of a magnet (3)

Answer 1

• 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

Question 2

What is a Permanent magnet

Answer 2

Produces its own magnetic field

Question 3

What is an Induced magnet

Answer 3

Is a material that becomes a magnet when it is placed in a magnetic field

Question 4

induced magnetism

Answer 4

Induced magnetism always causes a force attraction - when removed from the magnetic field an induced magnet loses most/all of its magnetism quickly

Question 5

Magnetic field

Answer 5

Is the region around a magnet where a force acts on another magnet or on a magnetic material (iron, steel, cobalt and nickel)

Question 6

What is the force between a magnet and magnetic material

Answer 6

Is always a force of attraction

Question 7

What does the strength of the magnetic field depend on

Answer 7

The distance from the magnet - the field is stronger at the poles of the magnet

Question 8

Direction of the magnetic field at any point (2)

Answer 8

• 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

Question 9

Magnetic compasses (2)

Answer 9

• Contain a small bar magnet

* The compass needle points in the direction of the Earth’s magnetic field

Question 10

How to plot the magnetic field of a magnet using a compass

Answer 10

Move compass around a magnet and trace its position on some paper to build up a picture of what the magnetic field looks like

Question 11

Draw Magnet field pattern of a bar magnet

Answer 11

Check photos

Question 12

How is the behaviour of a magnetic compass related to evidence that the core of the Earth must be magnetic

Answer 12

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

Question 13

What happens when a current flows through a conducting wire

Answer 13

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

Question 14

Shaping of a wire to form a solenoid

Answer 14

Increases the strength of the magnetic field created by a current through the wire - the magnetic field inside a solenoid is strong and uniform

Question 15

Magnetic field around a solenoid (2)

Answer 15

• Has a similar shape to that of a bar magnet

* Adding an iron core increases the strength of the magnetic field of a solenoid

Question 16

Electromagnet

Answer 16

Is a solenoid with an iron core

Question 17

Describe how the magnetic effect of a current can be demonstrated (right-hand thumb rule) (2)

Answer 17

• 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)

Question 18

Draw magnetic field pattern for a straight wire carrying current

Answer 18

(Check photos)

Question 19

Draw magnetic field pattern for a solenoid

Answer 19

Check photos

Question 20

Motor effect

Answer 20

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

Question 21

What does Fleming’s left-hand rule represent (3)

Answer 21

• The relative orientation of the force
• The current in the conductor
• The magnetic field

Question 22

Factors that affect the size of the force on the conductor (3)

Answer 22

• Magnetic flux density
• Size of current through the conductor
• The length of the conductor

Question 23

Equation linking force, magnetic flux density, current and length

Answer 23

Force (N) = magnetic flux density (T) x current (A) x length (m)

Question 24

The basis of an electric motor

Answer 24

A coil of wire carrying a current in a magnetic field tends to rotate

Question 25

Explain how the force on a conductor in a magnetic field causes the rotation of the coil in an electric motor (5)

Answer 25

• 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