General Knowledge

Question 1

What holds the electron in orbit around the nucleus?

Answer 1

A force of attraction

Question 2

Potential difference will exist between two points in the circuit that have a?

Answer 2

Difference in charge

Question 3

to produce a Voltage chemically, the two metals need to be made of?

Answer 3

Dissimilar metals

Question 4

Name 3 requirements needed to produce voltage by induction

Answer 4

1: Electrical conductor
2: Magnetic field
3: Relative movement

Question 5

What are the lines of force that pass through a space surrounding a magnet called?

Answer 5

Lines of magnetic flux

Question 6

3 materials that mixed with steel, will produce stronger magnets

Answer 6

Aluminium
Cobalt
Nickel

Question 7

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

Answer 7

Lines of magnetic flux

Question 8

There are 3 requirements needed for magnetism to produce voltage by induction, they are?

Answer 8

Conductor
Magnetic field
Relative movement

Question 9

What direction does AC travel through a conductor?

Answer 9

Both ways ( it alternates)

Question 10

List 2 advantages of AC over DC

Answer 10

Wiring & equipment can be lighter.

Easier to transform

Question 11

The level to which the voltage or current rises to is called?

Answer 11

Amplitude

Question 12

How are AC cycles per second expressed?

Answer 12

Hertz

Question 13

What are the values of the ships main electrical supplies?

Answer 13

3 Phase
450 V
60 Hertz

Question 14

What is the frequency equation?

Answer 14

Time (Seconds) = I ^divided Frequency

Question 15

List 4 advantages of an AC motor

Answer 15

1. Less maintenance
2. More efficient
3. Cheaper
4. More compact

Question 16

What is the main disadvantage of AC?

Answer 16

It’s difficult to vary speed

Question 17

List the 2 main components of an AC motor

Answer 17

• Stator
• Rotor

Question 18

What causes movement in a 3 phase induction motor?

Answer 18

The rotating magnetic field generated by the stator

Question 19

What is the most common AC motor used in the navy?

Answer 19

Squirrel Cage

Question 20

List the components of a Squirrel cage

Answer 20

1. Non drive end bearing
2. Copper end ring
3. Copper bars
4. Drive end bearing

Question 21

How does the rotating magnetic field from the stator cause the rotor to rotate?

Answer 21

1. The rotating field induces a current
2. The current causes a magnetic field
3. The interaction between the two magnetic fields causes the rotor to ‘follow’ the rotating field.

Question 22

What will happen if a running 3 phase AC motor were to lose 1 phase of input?

Answer 22

• Keep running
• Lose power
• Vibrate
• Create excessive noise
• Heat up

Question 23

What is Back EMF?

Answer 23

It is opposite in polarity to the EMF that is being applied to the conductor

Question 24

What position must the carbon brushes be fixed and why?

Answer 24

• MNA (Magnetic neutral axis)
• To stop sparking of the brushes

Question 25

What are Inter-Poles and what do they do?

Answer 25

* They assist in giving sparkless commutation, by neutralising the effect of armature reaction. * _They are poles similar to the main poles but smaller_

Question 26

What is the name given to materials in a solar panel?

Answer 26

Semiconductors

Question 27

What's the difference between **Volts**, **Watts** And **Current**?

Answer 27

* **Voltage** (Volts) is like water pressure in a pipe, i.e. How hard is the electricity pushing? * **Current** (Amps) is like the volume of water flowing in a pipe i.e. How much water is flowing? * **Power** (Watts) is the product of the two, when you multiply Voltage by Current you get Power.

Question 28

What is Torque?

Answer 28

a force that tends to cause rotation.

Question 29

What is an armature?

Answer 29

**a device through which electric current is passed for generating torque (rotor)**.

Question 30

What is magnetic flux?

Answer 30

Magnetic flux is ***a measurement of the total magnetic field which passes through a given area***

Question 31

What is the Magnetic Neutral Axis (MNA)?

Answer 31

**The axis on which there is no Flux generated in the armature conductors. Because they move parallel to the main field flux lines**.

Question 32

What is Field winding?

Answer 32

**Where the main field flux is produced**

Question 33

What are interpoles?

Answer 33

Interpoles are designed in DC motors To counter act armature reaction, they are smaller than the main poles

Question 34

What is Lamination for?

Answer 34

to improve efficiency of transformer

Question 35

What is torque?

Answer 35

Rotational forces

Question 36

Name the 3 classifications of DC motors.

Answer 36

1. Series 2. Shunt 3. Compound

Question 37

What is a secondary cell?

Answer 37

An electric cell that can be recharged and can be used to store chemical energy

Question 38

What is an electrolyte?

Answer 38

A liquid that can conduct electricity using a chemical reaction

Question 39

What is the difference between magnetic flux and magnetic field?

Answer 39

* **Magnetic field describes a region where a magnetic force can be felt.** * **Magnetic flux describes how much magnetic field passes through an area**

Question 40

What is an advantage of DC over AC?

Answer 40

Better speed control

Question 41

The amount of torque produced by a motor depends on?

Answer 41

* Strength of magnetic field * Size of the armature current

Question 42

Define power?

Answer 42

The rate of doing work

Question 43

Electric power depends on?

Answer 43

1. The number of electrons to be moved 2. The speed in which the are made to travel

Question 44

1 horsepower =?

Answer 44

746 watts

Question 45

Earth faults can be caused by?

Answer 45

* Dampness * Old, brittle insulation * Accidental damage

Question 46

A transformer consists of 2 coils close together but insulated from one another. What are they called?

Answer 46

Primary and secondary windings

Question 47

What is the equation for transformers?

Answer 47

Output V= No. secondary turns / No. primary turns x input V

Question 48

What is the purpose of a HF (High frequency) Generator?

Answer 48

To give voltage to the AVR

Question 49

The 3 sets of windings of a 3-phase motor are usually connected in 2 which ways?

Answer 49

1. Star 2. Delta

Question 50

Describe the Compound wound motor.

Answer 50

A combination of series and shunt. Has the best of both motors.

Question 51

Name the 2 neutral axis associated with DC motors

Answer 51

* Geometric neutral axis * Magnetic neutral axis

Question 52

what is another term for Commutator?

Answer 52

Split ring

Question 53

What is the difference between *Split ring* & **Slip ring**?

Answer 53

The **slip ring** is a closed circle (used in AC motors) The *Split ring* is divided (used in DC motors)

Question 54

Why wont DC current work with transformers?

Answer 54

because there is no change in the magnetic field