Section 6 - Electric And Magnetic Fields

Question 1

What is an electric field?

Answer 1

The region around an electrically charged object where if a second electrically charged object enters it, a force would be exerted on both objects.

Question 2

which direction do electric field lines go?

Answer 2

Positive to negative

Question 3

Which direction do magnetic field lines go?

Answer 3

North to south

Question 4

State the three main magnetic elements

Answer 4

Iron
Nickel
Cobalt

Question 5

How is an induced magnet created?

Answer 5

By putting a magnetic material inside a magnetic field

Question 6

The right hand thumb rule

Answer 6

Thumb = current
Fingers = magnetic field

Question 7

What happens when a current flows through a long, straight conductor?

Answer 7

A magnetic field is created

Question 8

What happens when a current-carrying conductor is put between two magnetic poles?

Answer 8

The two magnetic fields interact, causing a force on the wire.

Question 9

Fleming’s left hand rule

Answer 9

Thumb = motion
Index finger = Field
Middle finger = Current

Question 10

How do electric motors work?

Answer 10

A coil of wire is placed between two magnetic fields and a current is passed through it. Following the right hand thumb rule, the forces acting on the wire act in opposite directions causing the wire to spin. A split ring commutator swaps the contacts every half turn to keep the coil spinning in the same direction.

Question 11

What is magnetic flux density measured in?

Answer 11

Tesla

Question 12

What does a step up transformer do?

Answer 12

Increase the potential difference

Question 13

What does a step down transformer do?

Answer 13

Decrease the potential difference

Question 14

What kind of current does a dynamo create?

Answer 14

d.c

Question 15

What kind of current does an alternator generate?

Answer 15

a.c

Question 16

How does a dynamo work?

Answer 16

A coil is placed between two magnets, this causes the coil to spin. This induces a current in the coil. The current changes direction every half turn, but dynamos have a split ring commutator which swaps the connection to keep the current flowing in the same direction.

Question 17

How does an alternator work?

Answer 17

A coil is placed between two magnets, this causes the coil to spin, which induces a charge in the coil. They have slip rings and brushes so the contacts don’t change every half turn.

Question 18

How do microphones work?

Answer 18

Sound waves hit a flexible diaphragm which is attached to a coil of wire which surrounds one pole of a magnet. The diaphragm is moved back and forth by the sound wave, this generates a current in the coil.

Question 19

How does a loudspeaker work?

Answer 19

A coil is wrapped around one pole of a magnet. A a.c signal is passed through the coil, causing it to move back and forth. This movements make a cone vibrate, causing variations in pressure that cause sound waves.