Definitions

Question 1

What is the definition of power in terms of electrical forces?

Answer 1

It is the rate of working

Question 2

What are the four factors which determine the resistivity of a conductor?

Answer 2

M - Material
A - Area
L - Length
T - Temperature

Question 3

What unit is cable resistivity measured in?

Answer 3

Ω/m
Or ohms per metre

Question 4

How does one calculate the total resistance across both the cable and the load?

Answer 4

By adding together the resistance given by the load and the cable itself.
This can be calculated by using the R = V/I.

Question 5

How does one calculate the voltage drop across a load and the cable?

Answer 5

By adding together the total voltages used across the load and conductor and applying ohm’s law.

Question 6

What is Kirchoff’s voltage law?

Answer 6

All voltage drops across the circuit must equal the supply voltage.

Question 7

If a material is said to be ferromagnetic what does this mean?

Answer 7

It has a high susceptability to gaining/ being given a magnetic quality (that of repulsion or attraction to other magnetic objects).

Question 8

How do you create a permanent magnet?

Answer 8

By aligning the magnetic domains within the material using an external magnetic field.

Question 9

What is the magnetic field comprised of?

Answer 9

Lines of magnetic flux

Question 10

True or false:
Lines of magnetic flux can cross.

Answer 10

False.
They cannot cross.

Question 11

What determines the strength of a magnetic effect that a material exhibits?

Answer 11

The density of the lines of magnetic flux (Tesla).

Question 12

True or false:
Whenever you pass a current through a cable, a magnetic effect is created around it (lines of flux appear around the cable).

Answer 12

True.

Question 13

True or false:
The direction of current in a cable determines the direction of the flux.

Answer 13

True.

Question 14

In a diagram, what is denoted by a circle with a cross through it?

Answer 14

The current is flowing away from the observer.

Question 15

In a diagram, what is denoted by a circle with a dot in its centre?

Answer 15

The current is flowing towards the observer.

Question 16

What direction would the lines of magnetic flux flow if:
1. The current is flowing away from the observer.
2. The current is flowing towards the observer.

Answer 16

1. The lines of flux rotate in a clockwise fashion.
2. The lines of flux rotate in an anti-clockwise fashion.

Question 17

If the current of two cables are flowing away from the observer, would they attract or repel one another?
Why is this?

Answer 17

They would attract one another.
This is because the lines of flux are going in opposite directions, and as is the same with all magnetic effects, opposites attract.

Question 18

How would one make the magnetic effect caused by current flow, in any given cable with current passing through it, stronger?

Answer 18

Create a coil with the cable.

Question 19

True or false:
Adding an iron core to a coil of cable would reduce the amount of magnetic flux present.

Answer 19

False.
The amount of magnetic flux would increase.

Question 20

Briefly explain the right hand grip rule

Answer 20

Using your right hand, make a fist with your thumb pointing at a 90 degree angle.
Your fingers follow the path of current, and your thumb will point to the magnetic north of the resultant magnetic field.

Question 21

Which direction does magnetic flux flow outside of the magnet?

Answer 21

Outside of the magnet, the lines of flux flow from North to South.

Question 22

What makes a magnet stronger?

Answer 22

The density of the lines of magnetic flux will make the magnet stronger (β is a measure of the number of lines of flux (φ) in 1m²)

Question 23

If a current carrying conductor is placed in a magnetic field (north left, south right), and the current is flowing away from the observer, what will be:
1. The direction of motion of the conductor?
2. The direction of distortion of the magnetic field?

Answer 23

1. The conductor will move downwards
2. The magnetic field will be distorted upwards.

Question 24

If a current carrying conductor is placed in a magnetic field (north left, south right), and the current is flowing towards the observer, what will be:
1. The direction of motion of the conductor?
2. The direction of distortion of the magnetic field?

Answer 24

1. The conductor will move upwards.
2. The magnetic field will be distorted downwards.

Question 25

If a current carrying conductor is placed in a magnetic field (north right, south left), and the current is flowing away from the observer, what will be:
1. The direction of motion of the conductor?
2. The direction of distortion of the magnetic field?

Answer 25

1. The conductor will move upwards.
2. The magnetic field will be distorted downwards.

Question 26

How can you reverse the motion from a current carrying conductor inside a magnetic field without changing the direction of the current flow?

Answer 26

Changing the orientatin of the magnets, ie. flipping north and south.

Question 27

What (in principle) is the difference between a generator and a motor?

Answer 27

A generator converts mechanical energy into electrical energy.
A motor converts electrical energy into mechanical energy.

Question 28

Briefly describe Fleming’s left hand motor rule

Answer 28

Holding left hand out, thumb pointing 90° upwards, index finger pointing straight forwards, middle finger pointing 90° from the index.
Thumb represents direction of motion of conductor.
Index represents the North to South of the magnetic field.
Middle represents the direction of current.

Question 29

Briefly describe Fleming’s right hand generator rule

Answer 29

Holding right hand out, thumb pointing 90° upwards, index finger pointing straight forwards, middle finger pointing 90° from the index.
Thumb represents direction of motion of conductor.
Index represents the North to South of the magnetic field.
Middle represents the direction of current.

Question 30

What is the frequency of electricity in the UK?

Answer 30

50Hz

Question 31

How many ms does the electricity in the UK turn on and off?

Answer 31

Every 20ms

Question 32

How long is a period (frequency) in the UK?

Answer 32

1/50th of a second.

Question 33

230Vrms is the equivelant of ___

Answer 33

the heating effect of DC

Question 34

What is peak to peak voltage?

Answer 34

This is the highest and the lowest value that the voltage reaches over one cycle.