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da physics unit 2 ccea gcse > Electricity ⚡ > Flashcards

Electricity ⚡ Flashcards

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1
Q

Why are metals good conductors of electricity?

A

Metals are good conductors of electricity because they contain free electrons.

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2
Q

Why are insulators poor conductors of electricity?

A

Insulators such as plastic and rubber do not generally contain free electrons and so are poor conductors of electricity.

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3
Q

What are some good conductors of electricity?

A

Silver, copper, aluminium, steel, gold.

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4
Q

What are some insulators?

A

Rubber, plastic, glass, wood, marble.

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5
Q

What is electric current in a metal?

A

It is the flow of electrons.

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6
Q

What direction do the electrons flow in a circuit?

A

It was originally thought that the current was flowing in the opposite direction, i.e. from the positive terminal of the battery, through the conductor, to the negative terminal.

This is wrong but is still the direction of current marked on all circuit diagrams. It is called the direction of conventional current.

Electrons flow from the negative terminal through the conductor to the positive terminal.

They are repelled by the negative terminal and attracted by the positive terminal.

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7
Q

Why is a conductor needed in circuits?

A

To allow the flow of electrons.

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8
Q

What are the role of insulators in a circuit?

A

Insulators prevent the flow of electrons.

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9
Q

What is the role of switches in a circuit?

A

A switch is used to turn a circuit on (closed) and off (open).

When the switch is open, there is a break in the circuit and current stops flowing.

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10
Q

What is the symbol for a resistor?

A

—▭—

(Rectangle should be bigger).

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11
Q

What is the symbol of a variable resistor?

A

A rectangle with a diagonal arrow going through it.

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12
Q

What is the symbol of a switch?

A

Closed: a line with a circle attached to it on either side.

Example:

—⭕——⭕—

Open: the line is now diagonal to represent the break in the circuit. The line is attached to one circle now, however both circles haven’t moved.

Very bad example:

               /                      
    —⭕/     ⭕—
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13
Q

What is the symbol of a fuse?

A

A rectangle with a horizontal line through the middle.

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14
Q

What is the symbol of a voltmeter?

A

A circle with the letter V on it.

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15
Q

What is the symbol of an ammeter?

A

A circle with an A on it.

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16
Q

What is the symbol of a lamp?

A

A circle with an X through it.

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17
Q

What is the symbol of a cell?

A

——| █——

(The lines should be solid, the vertical lines should be a bit bigger).

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18
Q

What is the symbol of a battery?

A

——| █—–| █——

(All lines should be solid except the line in the middle, which should be dotted, the vertical lines should be a bit bigger).

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19
Q

What is cell polarity?

A

Batteries have a positive (+ve) terminal and a negative (-ve) terminal.

The positive terminal is represented by a long, thin line.

The negative terminal is represented by a shorter, thicker line.

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20
Q

What is the equation for charge?

A

Q = IT

21
Q

How do you work out the total voltage provided by a power source?

A

To work out the voltage provided by a power source you add the voltage of the individual cells connected in series.

Add = ——| █——| █——

Subtract= ——| █——█ |——

22
Q

Work out the total voltage:
3V 5V
+ +
——| █——| █——

A

3 + 5 = 8V

23
Q

Work out the total voltage:
3V 5V
+ +
——| █——█ |——

A

5 - 3 = 2V

24
Q

What is the equation for voltage?

A

V = IR

25
Q

What is a series circuit?

A

In a series circuit:

There is only one possible route for current to flow, thus the current through each component is the same.

The voltage of the supply is equal to the sum of the voltages across the separate components.

26
Q

What is a parallel circuit?

A

In a parallel circuit:

There is more than one route for current to flow.

The total current taken from the supply is the sum of the currents through the separate components.

The voltage across each component is the same as that of the supply.

27
Q

How do you calculate total resistance in series?

A

You add the individual resistances to get the total resistance.

RT = R1 + R2 etc.

28
Q

How do you calculate total resistance in parallel?

A

RT= R1 × R2 / R1 + R2

29
Q

How do you calculate total resistance if there is a series and a parallel circuit connected?

A

You need to first calculate the resistance of the parallel circuit as normal and then add it to the series resistance.

30
Q

What happens when electrical current flows through a metal wire and why?

A

Heat is generated due to the free electrons colliding more often and harder with metal atoms in the metal.

31
Q

What is the equation for energy?

A

E = PT

32
Q

What is the equation for power?

A

P = IV

33
Q

What is a.c.?

A

If the current constantly changes direction, it is called alternating current (AC). Mains electricity is an AC supply, with the UK mains supply being about 230V. It has a frequency of 50Hz, meaning that it changes direction, and back again, 50 times a second.

34
Q

What is D.C.?

A

If the current flows in only one direction it is called direct current (DC). Batteries and cells supply DC electricity, with a typical battery supplying around 1.5V.

35
Q

What would an D.C. supply look like on a diagram of CRO traces?

A

It would be a horizontal line.

36
Q

What would an A.C. supply look like on a diagram of CRO traces?

A

It would be a squiggly line.

37
Q

What is the unit of cost of electricity?

A

Kilowatt hour (kWh).

38
Q

What is a kilowatt hour?

A

A kilowatt is 1000 watts.

Kilowatt hour= 1000 × watts × time in hours

39
Q

How do you calculate the cost of using an appliance?

A

The power rating of electrical appliances can be used to calculate the cost of using them.

Equation:

Number of units used = power rating in kW x time in hours

When using this equation it is important to remember that the power must be in kW and the time in hours.

40
Q

What is a 1-way switch?

A

the switch basically operates as a make or break
switch, because:

• when it is turned on, the two terminals are
connected, and when it is turned off, the contact
between the two is broken.

• the switch is always placed on the positive or live
side of a circuit.

41
Q

What are the wires in a fused three-pin plug?

A

Earth wire, live wire, neutral wire.

42
Q

What is a live wire and what is its function?

A

The live wire is bRown and is to the Right (with fuse).

The live wire carries electricity to the appliance. It is connected directly to the generators of the electricity supply company.

43
Q

What is a neutral wire and its function?

A

The neutral wire is bLue and is to the Left.

The neutral wire returns the electricity to the generator after it has passed through the appliance, to complete the circuit.

The neutral wire is at approx 0V.

44
Q

What is the earth wire and its function?

A

The Earth wire is grEEn/yEllow and to the top.

The earth wire usually carries no electricity, it is there as a safety device.

45
Q

What are appliances with metal cases usually?

A

They are usually earthed.

46
Q

What is earthing?

A

You would get an electric shock if the live wire inside an appliance, such as a cooker, came loose and touched the metal casing.

However, the earth terminal is connected to the metal casing so that the current goes through the earth wire instead of causing an electric shock. A strong current surges through the earth wire because it has a very low resistance. This breaks the fuse and disconnects the appliance.

47
Q

What is double insulation?

A

Some appliances don’t have an earth wire. This is because they have plastic casings, or they have been designed so that the live wire cannot touch the casing. As a result, the casing cannot give an election shock, even if the wires inside become loose. These appliances have double insulation and carry a symbol.

The symbol is a hollow square that has 2 layers.

48
Q

What is the equation for power?

A

P = IV

49
Q

How do you choose the appropriate rating of a fuse?

A

Fuses are in amperes and to find current you need to use the equation:

I = P/V

For domestic fuses V = 230V (UK mains voltage).

P(the maximum power of the appliance) is marked on the appliance casing in watts.

da physics unit 2 ccea gcse (8 decks)

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