L Theory Flashcards by Kyle Burgher

What holds the electron in orbit around the nucleus

Force of attraction

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What is the outer obit of an atom called

Valance shell

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What is the polarity of an electron

Negative

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

Free electron

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If an electron is removed from a balanced atom, what is the stomach now know as

Positive ion (positively charged)

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Electrical flow is always ….

Negative to positive(-ve to +ve)

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If current was to flow from positive to negative(+ve to -ve) what is it called

Conventional current flow

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What is the symbol for current

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What is current measured in

Amps

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What is the electron called that is in the outer orbit of the atom

Valance electron

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Potential differnce will exist between two points in a circuit will have a …..

Difference in charge

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What is potential difference is measured in?

Volts

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What is the force that drives current round a circuit

Voltage

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Name 6 methods that can produce voltage

Induction heat
Friction pressure
Light chemical

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To produce voltage in a chemically, what do the different plates need to be made of?

Different metals

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Give an example of creating voltage using friction

Rubbing socks on a carpet

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Name 3 requirements for induction voltage

Relative movement
Magnetic field
Electrical conductor

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What determins the polarity of induced voltage

The movement of the conductor through the magnetic field

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What determines the voltage in a thermocouple

The differnce in temperature and the matrial used

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What is used in solar panels

Semiconductor

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A material with many free electrons will pass current freely is called a…

Conductor

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List at least 4 examples of conductors

Copper
Gold
aluminium
Steel
Carbon

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A material with few free electrons and can only pass with difficulty is called an….

Insulator

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Give at last 4 examples of insulators

Plastic
Fabric
Paper
Rubber
Glass

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List 4 examples of what could cause resistance in a circuit

Heat Cross face area Length Type of material

State ohms law

States that the current flowing through a conductor is directly proportional to the voltage applied across it. Providing the temperature remains constant, and is inversely proportional to the resistance

What is resistance measure in

Ohms

What is the formula for total resistance in a series circuit

Rt= R1+R2+R3

What is the equation for total resistance in a parallel circuit

RT=1/R1+1/R2+1/R3

Define electrical power

The rate of doing work Power=(force×distance)÷time

What is the unit for power

Watts

How many Watts makes 1HP

746W

What's the danger of passing constant high current through a conductor

Can overheat and cause a electrical fire

Name two types of fuses

High Rupturing Capacity(HRC) Cartridge Fuse

What does the fuse protect

The power source

What happens to a HRC fuse when it blows

The powder covers and solidifies over the broken contacts and this prevents it from completing the circuit

What is the electrical potential of the sea

0volts

3 things that can cause a earth fault

Dampness Accidental damage Insulation becoming brittle with age or heat

Why is equipment earthed to the ships hull

Because the Hull is at earth potential thus 0 volts meaning someone standing on earth cannot be shocked from touching casing

What is the name of the natural magnetic ore

Magnetite

What direction do lines of magnetic flux travil

North to South Negative to positive

List at least 3 materials mixed with steel, will produce stronger magnetics

Copper Iron Nickle Cobalt Aluminium

What is produced around a conductor passing current

Magnetic field Heat

Permanent and electro-magnet are two ways of producing magnets what's the third

Temporary magnet

List 2 advantages of AC over DC

Can transformed to get a range of voltage via a transformer Equipment is usually lighter

At what speed is ac changing direction called(measured in)

Frequency

The level to which the voltage raises to in an ac wavelength graph

Peak value

How are AC cycles expressed(unit of measurement)

Hertz

What are the values of the ships electrical supplies draw

450V 60Hz 3 phase

Draw the frequency equation

(Seconds) Time= 1 Frequency

What is the unit of inductance and what are the more common values

Henry Milli Henry Micro Henry

Label all parts of ac waveform

One cycle +peak value -Peak value Amplitude Time axis

Will a transformer work with dc current

Why won't dc work with a transformer

They only work with AC as it is always changing which gives us our relative movement

Name two types of transformers

Shell Core

What is the purpose of a transformer

To either increase or decrease the voltage

What is the purpose of a laminated soft iron core

It passes the magnetic field and voltage from one coil with another

State the output voltage equation

Output. No. of secondary coils = ×input volts Volts. No. Of primary coils

Purpose of a centre tapped transformer

Has an earth centre in the secondary coil, which half's the voltage This reduces the shock effect by half

Identify the input and output cables on hm ships

Input. Output Red- L1. A Yellow- L2. B Blue. - L3. C

What are the new colour codes

Red is now brown Yellow is now black Blue is now gray

What the most common type of generator today

Brushless generator

2 things EMF output depends on

1)Amount of lines of force cutting across the conductor as they rotate 2) the speed the generator is rotating

How is the HF generator turned

Is belt driving, its output is 115volts

What current is fed to the exciter stator

Direct current

What is the purpose of the rectifier assembly

Converts ac output to DC for the main generator rotors

If the magnetic field around the around the ac generator is stable(made from DC supply) how does the generator produce ac output

The last generator produces an AC output as the rotor rotates round 3 AC stator, producing 3 Phase AC current

What is the output from generators on hm ships and how does the AVR know what's being produced

450V 60 hertz 3 phase It is connected to the 3 phase by a sensing line

Lists 4 advantages of AC motors

Less maintenance More efficient than smaller dc motors Cheaper than DC More compact

What is the main disadvantage of an AC motor

Needs specialist equipment to vary speed

List the 2 main components of a AC motor

The stator The rotor

What causes the movement in a 3-phase induction motor

Rotating magnetic field

What is the most common type of AC motor used on hm ships

Squirrel cage induction motor

List the components of a squirrel motor (4)

Copper end ring Drive end bearing No drive end bearing Copper bars

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

It has the opposite polarity of the stator magnetic field, and the interaction of the two fields causes the rotor to turn to follow the rotating field

Why are there less maintenance on a AC motor

There is no electrical connection(carbon contacts) meaning you don't need brushes and slip rings, simplifying construction and less parts to wear

What would happen to a running 3 phase motor if it lost 1 phase

It would start vibrating and loose power and start overheating

If a shutdown 3 phase motor looses 1 of its phases what affect would this have

It wouldn't start

What is the DC motor generally made from

Coils of wire

What does maxwell right and grip indicates

Direction of the magnetic field around the conductor

What will lines of magnetic flux never do

Cross

Using flaming left hand rule. What does each digit indicate

Thumb= motion First finger= field Second finger= current

What is back EMF

Is the emf created by the generator that flows in a differnt direction to the EMF.

What is The amount of torque produced dependant on(2)

Strength of the magnetic field Magnitude of the armature current

List 3 classifications of DC motors(type)

Series wound Shunt wound Compound wound

Why must the carbon brushes fixed in the same position as and why

The must be fixed directly opposite along the magnetic neutral axes and this is to prevent any back EMF

Describe armature reaction

A magnetic field is created around the armature. The armature magnetic field will distort the winding magnetic field

What are inter-poles and where are they positioned and why

Inter-poles are similar poles just smaller. They are placed between the main poles and wound in series with the armature. They neutralise the effect of armature reaction

L Theory Flashcards

(88 cards)