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Physics > Electricity > Flashcards

Electricity Flashcards

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0
Q

Define the kilowatt hour (kWh)?

A

A unit of energy equal to 3.6MJ or 1kW for 1hour.

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1
Q

What is meant by a ‘230V, 25W’ for an appliance?

A

When connected to the 230V supply, the power (energy per second) is 25W.

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2
Q

Define intensity?

A

Intensity is the incident energy per unit area per second.

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3
Q

What is a current?

A

A flow of charge.
In a metal due to flow of electrons.
In an electrolyte due to flow of +ve and -ve ions.

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4
Q

Direction of conventional current?

A

Positive to negative

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5
Q

Direction of electron flow?

A

Negative to positive

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6
Q

What is a coulomb?

A

One coulomb is the charge which passes a point when a current of 1A flows for 1s

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7
Q

Charge =

A

Current x time

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8
Q

What is the elementary charge?

A

Minimum charge something can have - 1.6x10^-19C

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9
Q

What is does Kirchhoffs first law state?

A

That the sum of the current entering any point in a circuit is equal to the sum of the currents leaving that same point.

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10
Q

Current in a conductor:

I = ?

A

Anev

A is area
n is the number density
e is elementary charge
v is mean drift velocity

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11
Q

How should you attach an ammeter?

A

In series

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12
Q

How should you connect a voltmeter?

A

In parallel

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13
Q

What is 2.00mm^2 in metres?

A

2x10^-6

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14
Q

What is the shape of a diode?

A

Triangle with flat line on pointy end

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15
Q

If a thermistor heats up, what happens to the resistance through it?

A

Temperature rises, resistance falls, current rises

After x amount of time, resistance will become constant because thermal equilibrium will be reached

16
Q

How do LDR’s work?

A

As light intensity increases, resistance falls

17
Q

Define emf?

A

The energy transferred per unit charge when another type of energy is converted into electrical energy

18
Q

How do you work out the power dissipated by a resistor?

A

Current (through resistor) x voltage (across resistor)

19
Q

What is mean drift velocity?

A

The average velocity that an electron attains when an electric current flows.

20
Q

Giving examples, what are the differences between conductors, insulators and semi conductors?

A

Conductors (eg. Copper) contain a high number density of conducting electrons.

Insulators (eg. Rubber) contain very few or no conducting a electrons

Semiconductors (eg. Silicon) materials that have increasing conductivity with temperature, so a medium number density

21
Q

Define potential difference?

A

The electrical energy transferred per unit charge when electrical energy is converted into another form of energy

22
Q

Define the volt?

A

One volt is 1joule per coulomb

23
Q

W=

A

Voltage x charge

W is work done

24
Q

Define resistance?

A

The opposition to a flow of charge

25
Q

Define the ohm?

A

The resistance when 1volt produces 1amp of current

26
Q

What is ohms law and how can you tell if it is obeyed in a circuit?

A

Electrical current is proportional to voltage.

Straight line graph through origin

27
Q

Benefits of LEDs?

A

Long lifespan
Energy efficient
Only works one way round (positively biased)
Has a threshold voltage
Lots of different colours that require different voltages

28
Q

What happens to the resistance of s material when it’s temperature increases?

A

Resistance increases

29
Q

How is an NTC thermistor affected by temperature?

A

When temperature increases, resistance decreases.

30
Q

How does a fuse work?

A

A fuse is fitted in an electrical circuit to protect wiring from excessive current (and therefore helps to prevent excessive heat and fires).

Inside the fuse cartridge is a thin wire which gets hot and melts when the current gets too high, thus breaking the circuit. Each fuse has a max current it will permit.

31
Q

What is Kirchhoffs second law?

A

The sum of all of the emfs around a circuit are equal to the sum of all the pds around the same circuit.

32
Q

What is terminal pd?

A

The pd across the external resistor connected to an emf source.

Physics (12 decks)

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