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Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

What is the function of the live wire and what colour is it?

A

It is connected to the national grid and supplies electricity It is brown

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2
Q

What is the function of the neutral wire and what colour is it?

A

It is a return wire It is blue

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3
Q

What is the function of the earth wire and what colour is it?

A

It is a low resistance connection straight to the earth. This way, if a fault develops, a the large current will flow towards the earth and blow a fuse or a circuit breaker. It is green and yellow (striped)

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4
Q

What is the function of a fuse or circuit breaker?

A

To break the circuit when the current exceed a certain value

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5
Q

What are the common fuses in the UK and what are they used for?

A

3A (for lighting) 13A (for everything else)

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6
Q

Where do fuses/circuit breakers have to be connected and why?

A

They must always be connected to the live side because it is this section that supplies the electricity and has to be cut off

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7
Q

Some electrical appliances are not earthed, what do thy have instead?

A

Double insulating

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8
Q

What is double insulating?

A

As well as the wiring inside being insulated there is a casing made out of an insulating material (usually plastic) that stops current from reaching the person touching the appliance.

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9
Q

Why does current increase temperature when passing through a conductor?

A

Because electrons have kinetic energy and when they move some of this energy is passed on to the atoms in the conductor, which increases the amplitude of vibration of the atoms

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10
Q

What ubit is power measured in?

A

Watts (W)

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11
Q

What I’d the relationship between energy, voltage, current and time?

A

Energy = voltage x current x time (s) OR Energy = power x time (s)

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12
Q

Why is energy measured in?

A

Joules (J) OR Kilowatt-hours (kWh)

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13
Q

How do you convert from kWh to J

A

Multiply the amount of Watts (W) by 1 hour (60 x 60s) E.g. 1kWh = 1000W x 3600s = 3,600,000J or 3.6MJ

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14
Q

What are the characteristics of p.d. and current in a series circuit?

A

The current is the same every where The p.d. splits up so that the sum of p.d.s across individual components is equal to the p.d. across the power supply.

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15
Q

What are the characteristics of p.d. and current in a parallel circuit?

A

The current splits up so that the sum of the currents in each individual branch is the equal to the current drawn from the power supply The p.d. across each branch is the same

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16
Q

What is charge measured in?

A

Coulombs

17
Q

What’s the relationship between charge current and time?

A

Charge = current x time

18
Q

What is electric current in solid metal conductors?

A

A flow of negatively charged electrons from the negative terminal of the battery/power supply.

19
Q

What relationship do electrons have with the negative terminal an the positive terminal in the battery/power supply?

A

The electrons (which are negatively charged) are repelled from the negative terminal and attracted To the positive terminal.

20
Q

What do the arrows drawn on circuit represent?

A

The conventional current

21
Q

What is the conventional current?

A

The opposite direction to the flow of electrons through a circuit.

22
Q

In an electrolytic solution or an ionised gas which way to the electrons flow?

A

The negative ions flow towards the positive terminal and the positive ions flow in the direction of conventional current (towards the negative terminal)

23
Q

In what things are there both positive and negative ions? What are the ions called?

A

Electrolytic solutions and ionised gases Cations and anions

24
Q

How does the resistance of a metal wire at a constant temperate change as the voltage across it is varied?

A

IT DOESN’T change The resistance remains the same if it is at a constant temperature

25
Q

What is the relationship between current and voltage in a circuit if the voltage is varied across the wire (at a constant temperature)? What is this relationship known as?

A

Current is proportional to voltage Ohm’s law

26
Q

What would a current-voltage graph look like if it showed the resistance of a wire at a constant temperature? What does the gradient represent?

A

A straight line through the origin The gradient represents the resistance

27
Q

What is the relationship between resistance, voltage and current?

A

Resistance = voltage/current

28
Q

How does the resistance of a (filament) light bulb change as the voltage is varied and why?

A

The resistance increases because the temperature increases in the bulb. This happens because the moving electrons collide more with the metal ions causing resistance. As temperature increases they have more energy and therefore more collisions.

29
Q

What would be the shape of a current-voltage graph for a bulb?

A

The line would have a steep gradient at first and then curve over.

30
Q

What happens to the resistance of a semiconductor (silicon) diode as the voltage across it is varied?

A

The resistance drops.

31
Q

What would the shape of a current-voltage graph look like for a semiconductors diode?

A

The line will be horizontal (0 current) until it curves upwards suddenly.

32
Q

What is a resistor designed to do?

A

To control the amount of current flowing in a circuit.

33
Q

What effect does the passage of electrical current have on conductors and why?

A

A heating effect is produced because electrons have kinetic energy which is passed to the atoms in the conductor as collisions occur.

34
Q

What units is resistance measured in?

A

Ohms

35
Q

How does an LDR operate?

A

The resistance drops as the light levels increase.

36
Q

How does a thermistor operate?

A

Resistance drops as temperature increases.

37
Q

What can be used to indicate the presence of current in a circuit?

A

LEDs

Physics (8 decks)

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