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Electricity Flashcards

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1
Q

Describe the difference between a series circuit and a parallel circuit.

A

A series circuit contains only one loop of wire.

A parallel circuit contains two or more loops (branches) of wire.

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2
Q

What is an electric current?

A

An electric current is the flow of charge, usually electrons.

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3
Q

State the equation that links charge flow, current and time

A

Q = I t

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4
Q

Calculate the current in a circuit if a charge of 4 C flows in 20 seconds.

A 
Q = I t
I = Q / t	or 	I = 4 / 20
I = 0.2 A
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5
Q

In a lightning bolt, a charge of 15 C flows and there is a current of 30,000 A. Calculate the duration of the lightning strike.

A 
t = Q / I
t = 15 / 30 000
t = 0.0005 s     or     0.5 ms
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6
Q

What is an ohmic conductor?

A

A material where the current through the material is proportional to the potential difference applied across its ends.

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7
Q

Describe how the currents in a series circuit and a parallel circuit differ.

A

Series circuit – same current at any point of the loop.

Parallel circuit – the total current through the whole circuit is the sum of the currents in each loop.

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8
Q

Two resistors are placed in parallel as shown in the diagram below. Why will the maximum resistance of the circuit be less than 22 kΩ?

A

It will be less than 22 kΩ because the total resistance of two resistors in parallel is less than the resistance of the smallest individual resistor.
The smallest individual resistor is 22 kΩ.

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9
Q

What does a.c stand for?

A

Alternating current

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10
Q

What does d.c stand for?

A

Direct current

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11
Q

Give an example of where a.c is used

A

Mains electricity

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12
Q

Give an example of where d.c is used.

A

Batteries

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13
Q

Describe the difference between an alternating potential difference and direct potential difference. You may draw a sketch graph to help answer the question.

A

An alternating potential difference will go from positive to negative repeatedly
Producing an alternating current in a circuit.
A direct potential difference will stay either positive or negative, but not change sign
Producing a direct current in a circuit.

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14
Q

What is the frequency and potential difference of mains electricity in the U.K?

A

Frequency 50Hz

Potential difference 230V

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15
Q

What is the colour of a live wire?

A

Brown

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16
Q

What is the colour of a

neutral wire?

A

Blue

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17
Q

What is the colour of a earth wire?

A

Yellow/Green

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18
Q

What is the function of the live wire?

A

Carries alternating potential difference from the supply.

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19
Q

What is the function of the neautral wire?

A

Completes the circuit.

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20
Q

What is the function of the earth wire?

A

Safety wire to stop appliance becoming live.

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21
Q

State the equation that links power, potential difference and current. Include equation symbols and units.

A 
Power = Potential Difference x Current 
P = V I
22
Q

State the equation that links power, current and resistance. Include equation symbols and units.

A 
Power = (current)2 x Resistance
P = I2 R
23
Q

What is the unit symbol for power?

A

W

24
Q

What is the unit symbol for potential difference?

A

V

25
Q

What is the unit symbol for current?

A

A

26
Q

What is the unit symbol for resistance?

A

Ω

27
Q

What is the unit for resistance?

A

Ohms

28
Q

What is the unit for current?

A

Amp

29
Q

What is the unit for potential difference?

A

Volts

30
Q

What is the unit for power?

A

Watts

31
Q

What is the unit for resistance?

A

Energy transferred = Power × Time
E = P t
Energy transferred = Charge flow x Potential difference
E = Q V

32
Q

What is the unit for power?

A

Watts

33
Q

What is the unit for energy transferred?

A

Joules

34
Q

What is the unit for time?

A

Seconds

35
Q

What is the unit for charge flow?

A

Coulombs

36
Q

What is the unit for potential difference?

A

Volts

37
Q

What is the unit symbol for energy transferred?

A

J

38
Q

What is the unit symbol for power?

A

W

39
Q

What is the unit symbol for time?

A

S

40
Q

What is the unit symbol for charge flow?

A

C

41
Q

What is the unit symbol for potential difference?

A

V

42
Q

A kettle has a power rating of 1.2 kW.
The kettle runs on mains electricity at 230 V.
Work out the current flowing through the kettle when in use.

A

5.2 A
1.2 kW = 1200 W
Power = Potential difference x Current
Current = power / potential difference or current = 1200 / 230

43
Q

A kettle has a power rating of 1.2 kW.
The kettle runs on mains electricity at 230 V.
The kettle takes 1 minute and 20 seconds to boil some water.
Work out the energy transferred by the kettle in this time.

A

96 000 J
Energy transferred = Power x Time
Energy transferred = 1200 x 80

44
Q

Describe fully how electricity is transmitted from power stations to our
homes.

A

A step-up transformer is used to increase potential difference / decrease current
Electricity transmitted along power cables (at high potential difference)
Step-down transformers used to decrease the potential difference before the electricity enters homes.

45
Q

Explain why a step-up transformer is used when transmitting electricity long distances across the UK.

A

Increasing the potential difference will decrease the current
Lower currents mean less heating of the power cables
So, less electrical energy wasted as heat
Making the transmission process more efficient.

46
Q

State the two types of electrical charge.

A

Positive and negative

47
Q

Describe what would happen if two like charged particles were placed near
each other.

A

Two like charges would repel away from each other.

48
Q

A balloon is rubbed on a jumper.
The balloon becomes positively charged.
Explain why the balloon gains a negative charge.

A

Electrons move from the jumper to the balloon

So there are more negative charges on the balloon than positive charges.

49
Q

Describe what would happen if a charged rod was placed above a pile of dust.

A

The dust will attract to the rod

Note: The dust will stick to the rod is not an acceptable answer.

50
Q

What is an electric field?

A

An electric field is the space around a charged object that will exert a force upon another charged object that is placed there.

51
Q

Mike gets off a trampoline and gets an electric shock. Mike sees a spark pass between himself and the trampoline.
Explain why the spark formed in the air between Mike and the trampoline.

A

The electric field strength of Mike as a charged object
Is greater than the dielectric field strength of air
Causing an increase in the number of free electrons in the air
Allowing the air to conduct
And a spark to form.

Physics (4 decks)

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