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Physics > Topic 2 - Electricity > Flashcards

Topic 2 - Electricity Flashcards

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1
Q

What is needed for charge to flow through a closed circuit?

A

A source of potential difference.

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2
Q

What is electric current?

A

The rate of flow of electric charge.

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3
Q

How can you measure charge flow?

A

Charge flow [Q] (in Coulombs, C) = current [I] (in Amperes, A) x time [t] (in seconds, s)

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4
Q

What so the value of the current in a single closed loop?

A

Current has the same value at any point.

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5
Q

What does current through a component depend on?

A

Resistance of the component and potential difference across the component.

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6
Q

What happens to current for a given potential difference when there is high resistance?

A

Current will decrease.

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7
Q

How do you work out potential difference?

A

Potential Difference [V] (in volts, V) = current [I] (in Amperes, A) x resistance [R] (in Ohms)

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8
Q

What does a variable resistor do?

A

A variable resistor allows resistance onto change as the current changes.

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9
Q

What is the name of the component that makes sure resistance is kept them same?

A

Fixed resistor.

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10
Q

The current through an ohmic conductor - at a constant temperature - is what to the potential difference across the resistor?

A

Directly proportional.

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11
Q

What does current being directly proportional to potential difference mean?

A

That resistance remains constant as current changes.

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12
Q

What happens to resistance of components such as lamps, diodes and thermistors?

A

It is not constant and changes with the current through the component.

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13
Q

What happens to the resistance of a filament lamp as the temperature of it increases?

A

The resistance also increases.

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14
Q

How does current flow through a diode?

A

In one direction.

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15
Q

What happens to resistance when a diode is in the reverse direction?

A

It is very high.

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16
Q

What happens to the resistance of the thermistor and temperature increases?

A

Resistance decreases.

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17
Q

What happens to the light intensity of an LDR when resistance decreases?

A

Light intensity increases.

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18
Q

What happens to current, potential difference and resistance through components connected in series?

A
  • current is the same
  • total potential difference is shared between components
  • total resistance of tow components is the sum or the resistance of each component
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19
Q

What is the equation for total resistance of a series circuit?

A

RT = R1 + R2

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20
Q

What happens to current, potential difference and resistance through components in a parallel circuit?

A
  • total current is the sum of currents through separate components
  • potential difference is the same
  • total resistance of two resistors is less than the resistance of each component
21
Q

What is the equation to work out resistance in a parallel circuit?

A

1/RT = 1/R1 + 1/R2

22
Q

What is mains electricity supply?

A

Alternating current (AC)

23
Q

What is the hertz and voltage of U.K. means supply?

A

50Hz and 230V

24
Q

What factors affect resistance?

A
  • length of wire

- whether components are in series of parallel

25
Q

Explain the differences between AC and DC.

A
  • AC - alternating current is constantly changing direction (produced by alternating voltages where the positive and negative ends alternate).
  • DC - direct current always flows in the same direction, created by direct voltage.
26
Q

Describe and label the three wires in a mains plug.

A

LIVE WIRE - brown
EARTH WIRE - yellow + green
NEUTRAL WIRE - blue
(Insulating cover coloured for easy identification)

27
Q

What is the role of the live wire?

A

It carries the alternating potential difference from supply.
It is 230V.

28
Q

What does the neutral wire do?

A

Completes the circuit.

It is 0V.

29
Q

What is the role of the earth wire?

A

Safety wire to stop the appliance from becoming live.
It is 0V.
(Only carries current if there is a fault)

30
Q

What are the dangers of the live wire to humans?

A

It can give you electric shocks.
Your body is 0V so when you touch the live wire 230V are flowing through you, this could injure or kill you.
Even if the switch is turned off, there is still danger - there is no current but there is PD and your body would provide the link for it to flow.

31
Q

What are the dangers of connection between the live wire and the earth wire?

A

If it creates low resistance, a huge current will flow and can cause a fire.

32
Q

Explain how power is transferred in any device.

A

The total energy transferred depends on how long the appliance has been on for and its power.

33
Q

State the two equations for power.

A

Power [P] (in watts, W) = potential difference [V] (in voltage, V) x current [I] (in Amperes, A)

Power = (current (squared)) x resistance [R] (in ohms)

34
Q

How do domestic appliances transfer energy from AC/DC to kinetic energy of electric motors?

A

Through a step-up or step-down transformer.

35
Q

When is work done in a circuit?

A

When charge flows.

36
Q

How can you calculate energy transferred?

A

Energy transferred [E] (in Joules, J) = power [P] (in Watts, W) x time [t] (in seconds, s)

Energy transferred = charge flow [Q] (in coulombs, C) x potential difference [V] (in volts, V)

37
Q

What is the National Grid?

A

A system of cables and transformers connecting power stations to consumers.

38
Q

What does the National Grid transfer to consumers?

A

Electrical power.

39
Q

What do STEP-UP transformers do?

A

Increase voltage form power stations to transmitting cables.

40
Q

What do STEP-DOWN transformers do?

A

Decrease voltage for domestic use.

41
Q

Why is the National Grid and efficient way to transfer energy?

A

High voltages are needed to transmit electricity as it reduces heat loss and therefore improves efficiency.

42
Q

How is static electricity formed?

A

When some insulating materials are rubbed together they become electrically charged - negatively charges electrons rub off one material (making it positively charged) and onto the other (making this one negatively charged)

43
Q

What happens when two electrically charged objects are brought close together?

A

They exert a force on each other:
same charge = repel
different charge = attract
These are non-contact forces.

44
Q

What causes a spark?

A

If the potential difference is large enough, electrons can jump the gap between the charged object and the earth.

45
Q

What do all charged objects create around them?

A

Electric fields.

46
Q

Where are electric fields strongest?

A

When they are closest to the charged object.

47
Q

How can you show and electric field around an object?

A

Drawing field lines.

48
Q

What happens when a second charged object is placed in the field?

A

A force is exerted on it, the force gets stronger and the object is closer.

49
Q

Using electric fields, explain sparking.

A

Sparks are caused when there is a high potential difference, which causes field lines between the charged object and the earthed object. The strong field causes electrons in the air particles to be removed (ionisation), when air is ionised a current can flow through it and create a spark.

Physics (9 decks)

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