Electromagnetic Effects

Question 1

If a conventional current is flowing away from you (x). Which way is the magnetic field?

Answer 1

Clockwise

Question 2

If a conventional current is flowing towards you (.). Which way is the magnetic field?

Answer 2

Anti clockwise

Question 3

Which rule is used to determine the magnetic flow around a conductor with a current flowing through it?

Answer 3

Right hand rule. Remember it is conventional current (the direction is from + towards -)

Question 4

A straight conductor is placed with current flowing from N to S.

A compass is placed under the conductor.

In which direction will the N arrow of the compass swing?

Answer 4

E

Question 5

A straight conductor is placed with current flowing from S to N

A compass is placed above the conductor.

In which direction will the N arrow of the compass swing?

Answer 5

E

Question 6

State the right hand rule

Answer 6

If a current flow along a conductor. One can use the right hand to determine the magnetic field by pointing the thumb in the direction of the current flow, the other curved fingers show the magnetic field direction.

Question 7

How can the field strength of a solenoid be increased

Answer 7

Number of turns increase

Increase the current strength

Placing a Soft iron metal core inside the solenoid

Question 8

How can one determine the direction of the field in a coil carrying a current

Answer 8

Right Hand Grasp rule

Question 9

Describe the right hand grasp rule

Answer 9

If a conductor (solenoid) is grasped in the right hand with the curved fingers around the coil and pointing in the direction of the conventional current, the thumb points towards the north pole

Question 10

Name 3 facts about the field of a solenoid

Answer 10

The field outside the solenoid is from N to S. The field inside the solenoid is from S to N

The field inside the solenoid is a uniform field because the magnetic lines are parallel to each other

The magnetic field inside the solenoid is stronger than outside because the field lines are closer together.

Question 11

Describe an electromagnet

Answer 11

It is a coil of wire through which an electric current is passed - wound around an iron core.

Question 12

How can an electromagnet’s strenth be strengthened

Answer 12

Increase the number of turns of wire

Increase the current strength

Use a soft iron metal as the core

Question 13

Name some advantages of a relay switch

Answer 13

One switch can control another without direct connection between them

The input switch can operate at a low voltage while switching a high voltage - safely

A small current on the input switch can switch a large current in the output circuit

Can be used as a level sensor

Can be considered a current amplifier

Question 14

Define the motor effect

Answer 14

Is the interaction between the magnetic field of a permanent magnet and the magnetic field of a current carrying conductor which causes movements

Question 15

State Flemmings left hand motor rule

Answer 15

If the thumb forefinger and middle finger of the left hand are held mutually at right angles,

the forefinger represents the direction of field

The middle finger represent the current

The thumb represents the force

Question 16

Two parallell conductors are conducting electricity in opposite directions, which way will they tend to move

Answer 16

Away from each other

Question 17

Two parallell conductors are conducting electricity in the same direction, which way will they tend to move

Answer 17

Towards each other

Question 18

In an electric motor, what does the armature consists of

Answer 18

Axle

Commutator

Coil

Question 19

What make contact with the commutators and needs replacement from time to time

Answer 19

Brushes

Question 20

The commutator consists out of two _______

Answer 20

Segments

Question 21

Describe how an electron moving through a magnetic field would be “bend”

Immagine the electron moving from left to right

The magnetic field coming out of the paper (.)

Answer 21

Will be deflected to the top

Question 22

Def Electromagnetic induction

Answer 22

Is the production of an EMF in a circuit which is caused by a changing magnetic field linking with the circuit

Question 23

How can the EMF of a electromagnetic induction be increased?

Answer 23

Increase the strength of the magnet

Increase the speed at which the magnet moves

Increase the number of turns on the coil

Question 24

State Lenz’s law

Answer 24

That the direction of the induced current is such that it sets up a magnetic field
That opposes the inducing action.

Question 25

What is generated around a conductor when electricity flows through it?

Answer 25

A magnetic field

Question 26

Define an ideal transformer

Answer 26

There is no Energy Lossess

Therefore the power generated in primary coil = power out of secondary coil

P= VI (primary)= VI (secondary)

Question 27

Name 3 experiments that demonstrate induction

Answer 27

By moving a permanent magnet and solenoid relative to each other

By switching an electromagnet on and off - with pick up coil close by

By alternating the current using a reostat

Question 28

How is efficiency calculated in a transformer

Some energy is lost between primary and secondary coils

Answer 28

Efficiency = energy in secondary/energy in Primary X 100

Question 29

What is meant by. Leakage of field lines

Answer 29

All the field lines of the primary coil may not link with the secondary coil

Then the efficiency of the transformer drops

Question 30

Name reasons for leakafe of field lines

Answer 30

1) . Poorly designed transformer

2) . Gaps between the coils

Question 31

Name the advantages of high voltage transmission lines

Answer 31

Less energy lossess due to heat loss
( P=I*2R)

Thinner cables can be used - more easily supported by pylons

Thinner cables and smaller pylons are more exonomical