L Theory

Question 1

What holds electrons in orbit around the nucleus?

Answer 1

A force of attraction

Question 2

What is the outer orbit of the atom called?

Answer 2

Valence shell

Question 3

What is outer electron in the atom called?

Answer 3

Valence electron

Question 4

What is the polarity of an electron?

Answer 4

Negative

Question 5

If an electronic is removed from an atom, what is it called?

Answer 5

Free electron

Question 6

If an electronic is removed from an atom, what is the atom called?

Answer 6

Positive ion

Question 7

Electrons flow from…?

Answer 7

Negative to positive

Question 8

What is conventional flow?

Answer 8

Positive to negative

Question 9

What is the circuit (equation) symbol for current?

Answer 9

I

Question 10

What is current measured in?

Answer 10

Amps

Amperes

Question 11

A material with lots of free electrons to allow current us called a….?

Answer 11

Conductor

Question 12

Give 4 examples of a conductor?

Answer 12

Copper
Gold
Brass
Steel

Question 13

A material with very few free electrons that doesn’t allow current through us called a…?

Answer 13

Insulator

Question 14

Give 4 examples of an insulator?

Answer 14

Rubber
Plastic
Wood
Paper

Question 15

What are the 4 factors that will effect the resistance of a conductor?

Answer 15

Length
Cross sectional area
Temperature
Type of material used

Question 16

How will increasing the length of a conductor effect the resistance?

Answer 16

Increase the resistance

Question 17

How would increasing the temperature change the resistance?

Answer 17

Increase of resistance

Question 18

How does increasing the cross sectional area effect the resistance of a conductor?

Answer 18

Decreases the resistance

Question 19

State ohms law in full

Answer 19

The current in a conductor is directly proportional to the voltage applied across it and inversely proportional to the resistance provided the temperature remains constant

Question 20

What is the unit of resistance?

Answer 20

Ohms

Question 21

State the formula for calculating resistance in a series circuit

Answer 21

Rt = R1 + R2 + ….

Question 22

State the formula for calculating the resistance in a parallel circuit

Answer 22

1/Rt = 1/R1 + 1/R2 + ….

Question 23

After working out the total resistance in a parallel circuit, what is a good check to see if you’re correct?

Answer 23

The total resistance is lower than the smallest resistor

Question 24

What is the name of a naturally magnetic ore?

Answer 24

Magnetite

Question 25

There are lines of force that surround a magnet, what are these called?

Answer 25

Lines of magnetic flux

Question 26

What direction do the lines of magnetic flux travel?

Answer 26

North to South

Question 27

What are 2 types of commonly used permanent magnet?

Answer 27

Bar | Horseshoe

Question 28

What will happen if 2 like poles are brought together?

Answer 28

They will repel

Question 29

What will happen if 2 unlike poles are brought together?

Answer 29

They will attract, stick together and magic stuff

Question 30

What are 3 materials that, when added to steel, make the magnet stronger?

Answer 30

Nickel Cobalt Aluminium

Question 31

What is produced around a conductor when a current is passed through it?

Answer 31

A magnetic field

Question 32

Name 3 methods of producing a magnet?

Answer 32

Permanent magnet Electro magnet Rubbing a permanent against a none magnetic iron bar

Question 33

What are the 3 requirements to induce a voltage by induction?

Answer 33

A conductor Relative motion Magnetic field

Question 34

Will a transformer work with DC? | Why?

Answer 34

No | Because it requires an alternating magnetic field created by AC flow

Question 35

List 2 types of transformer construction

Answer 35

Shell | Core

Question 36

What is the main purpose of a transformer?

Answer 36

To change the voltage of an AC line

Question 37

What us the purpose of the laminated iron core?

Answer 37

To reduce edicurrents which increases the efficiency

Question 38

If there are more coils on the secondary coil than in the primary, what type of transformer is it?

Answer 38

Step up

Question 39

State the output voltage equation?

Answer 39

(Number of primary coils/number of secondary coils) = (primary voltage/secondary voltage)

Question 40

What is the purpose of a centre tapped transformer?

Answer 40

Reduces the harm done by touching a live wire as it will halve the voltage across your body

Question 41

Identify the the cables used on a HM ship

Answer 41

Red - phase 1, L1 Yellow - phase 2, L2 Blue - phase 3, L3

Question 42

State the new colour codes for phases

Answer 42

Brown - phase 1, L1 Black - phase 2, L2 Grey - phase 3, L3

Question 43

What are the advantages of an AC motor?

Answer 43

Small Light Less maintenance More efficient

Question 44

What is the main disadvantage to an AC motor?

Answer 44

Difficult to vary speed output

Question 45

What are the 2 main components to an AC motor?

Answer 45

Stator | Rotor

Question 46

What causes motion in an induction motor?

Answer 46

The stator creates a rotating magnetic field The rotating magnetic field creates a current in the copper bars of the rotor The rotor generates a magnetic field which tries to follow the rotating magnetic field

Question 47

What is the most common types of AC motor on HM ships?

Answer 47

Squirrel cage motor

Question 48

List the components of a squirrel cage motor

Answer 48

``` Rotor Stator Free and shaft end bearings Free and shaft end copper rings Copper bars ```

Question 49

Why is there less maintenance on an AC motor?

Answer 49

No carbon brushes or commutator

Question 50

What would happen is a 3 phase motor was to lose a phase?

Answer 50

``` Vibrates Lots of noise Low power Will continue running Will heat up ```

Question 51

If a shut down 3 phase motor was to lose 1 phase, what would happen if you tried to start it?

Answer 51

It wouldn't start

Question 52

A potential difference will exist between 2 points that have a...?

Answer 52

Difference in charge

Question 53

What is potential difference measured in?

Answer 53

Volts

Question 54

What is the name of the force that drives a current through the circuit?

Answer 54

Electromotive force

Question 55

Name 6 methods of how voltage can be created

Answer 55

``` Light Induction Heat Friction Pressure Chemical ```

Question 56

To produce a chemical voltage, the 2 plates must be made of...?

Answer 56

Different metals

Question 57

Give an example of where friction creates voltage

Answer 57

Rubbing a woolen cloth on a glass rod and then dumping the electrons on a carbon rod

Question 58

What determines the polarity of an induced voltage?

Answer 58

The direction of polarity of the moving magnetic field

Question 59

What determines the voltage produced by a thermocouple?

Answer 59

The types of metal used | Heat difference

Question 60

What is a solar panel made of?

Answer 60

Semi conductor