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A Level Physics for AQA. > 3.5.1.1 Basics of Electricity > Flashcards

3.5.1.1 Basics of Electricity Flashcards

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1
Q

What is the definition of current?

A

Current is the rate of charge flow

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2
Q

What equation links Charge, Current and Time?

A 
Charge = Current x Time
Q = I x t
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3
Q

What is the SI Unit for Charge?

A

Coulombs (C)

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4
Q

What is the SI unit for current?

A

Amperes/ amps (A)

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5
Q

What is one coulomb equivalent to?

A

One coulomb is equivalent to the amount of charge that passes in 1 second when the current is 1 amp.

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6
Q

What is 1 amp equivalent to?

A

1 amp is equivalent to the 1 coulomb per second.

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7
Q

What is the direction of conventional current?

A

From the positive terminal of the cell, to the negative terminal of the cell.

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8
Q

What is the direction of electron flow? Why?

A

From the negative terminal of the cell to the positive terminal of the cell.
The electrons are repelled from the negative terminal and attracted to the positive terminal.

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9
Q

What is used to measure current?

A

An ammeter is used to measure the current in a circuit.

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10
Q

How should an ammeter be connected in a circuit and why?

A

Should be connected in series with the component it is measuring the current through.
The current in series is the same, therefore the current through the ammeter will be equal to the current through the component.

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11
Q

What is the definition of potential difference?

A

Potential difference is the work done per unit charge.

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12
Q

What equation links potential difference, work done and charge?

A

Work Done = Potential Difference x Charge

W = VQ

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13
Q

What is the SI unit for potential difference?

A

volts (V)

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14
Q

What is the SI unit for work done?

A

joules (J)

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15
Q

What is work done also known as?

A

Work done = Energy Transferred (E)

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16
Q

What do you need to do to a conductor to make electric charge flow through it?

A

You must do work on the conductor, or transfer energy to the conductor.

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17
Q

What is used to measure potential difference?

A

Voltmeter

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18
Q

How should a voltmeter be connected in a circuit and why?

A

A voltmeter should be connected in parallel to the component it is measuring the p.d, across.
The pd of components is the same.

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19
Q

What is 1 volt equivalent to?

A

1 volt = 1 joule of energy transferred per second.

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20
Q

What is resistance?

A

Resistance is a measure of how difficult it if for current to pass through a component.

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21
Q

What is the definition of the volt?

A

The potential difference across a component is 1 volt when you convert 1 joule of energy moving 1 coulomb of charge through the component.

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22
Q

What equation links potential difference, current and resistance?

A

Potential Difference = Current x Resistance

V = I x R

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23
Q

What is the SI unit for resistance?

A

Ohms (Ω)

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24
Q

What depends on resistance?

A

The amount of current which can pass through a material for a certain voltage depends on the resistance.

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25
Q

What is the definition of the ohm?

A

A component has a resistance of 1 ohm, if a potential difference of 1V causes a current of 1A to through it.

26
Q

What does Ohm’s Law states?

A

Ohms law states that:

Providing the external conditions remain constant, the current through a component is directly proportional to the potential difference across the component.

27
Q

What is an ohmic conductor?

A

An ohmic conductor is a conductor which obeys ohm’s law.

28
Q

What is constant for an ohmic conductor?

A

An ohmic conductor has constant resistance.

29
Q

Describe the I/V graph for an ohmic conductor.

A

The IV graph is a straight-line graph which goes through the origin.
As current increases on the y axis, the potential difference increases on the x axis.

30
Q

Name two possible physical conditions which may affect resistance.

A

Light intensity.

Temperature.

31
Q

What equation can be used to calculate the resistance of an ohmic conductor?

A

V = IR

Also called the ohm’s law equation.

32
Q

Describe briefly how you would find the resistance of an ohmic conductor connected to a source of potential difference.
State what you will use and which equation you would use.

A
  1. Connect the ohmic conductor to the source of potential difference.
  2. Connect an ammeter in series with the conductor.
  3. Connect a rheostat/variable resistor in series with the conductor.
  4. Connect a voltmeter in parallel across the conductor.
  5. Vary the current through the component using the rheostat.
  6. Start at the highest setting and decrease the resistance in regular intervals.
  7. Every time you decrease the resistance, record the reading of the voltmeter and ammeter.
  8. After taking multiple readings, plot a graph of current against potential difference (I/V).
  9. Find the gradient of the graph. The gradient is equal to 1/resistance.
33
Q

What are the characteristics of an ideal voltmeter have and why?

A

An ideal voltmeter would have an infinite resistance so that no current can pass through it.

34
Q

What are the characteristics of an ideal ammeter?

A

An ideal ammeter would have an zero resistance. so that the full amount of current supplied to the component by the cell can flow through it, and give the correct current reading.

35
Q

What is an LED?

A

A light emitting diode emits light when it conducts.

36
Q

What is a thermistor?

A

A thermistor’s resistance changes with temperature.

The resistance decreases with increasing temperature, but only if the thermistor’s is an intrinsic semiconductor.

37
Q

What is a series circuit?

A

A series circuit is a circuit with a single loop.

38
Q

What is an LDR?

A

A light dependant resistor.

Its resistance changes with light intensity. The resistance decreases with increasing light intensity.

39
Q

What is a parallel circuit?

A

A parallel circuit has multiple loops, or branches.

40
Q

What is a cell? What is a battery?

A

A cell s a source of electrical energy.

A battery is a combination of cells.

41
Q

What is needed to make an electric current pass through a circuit?

A

The circuit needs to be complete.

The circuit must have a source of potential difference.

42
Q

What causes current?

A

Current is due to the passage of charge carriers through a circuit.

43
Q

What are the charge carriers in metals?

A

The charge carriers in metals are conduction electrons.

They move around inside the metal, repeatedly colliding with each other and the fixed positive ions in the metal.

44
Q

How can charge carriers gain energy?

A

They can gain energy from cells, batteries and power sources.
They can also gain energy from solar cells, dynamos and thermocouples.

45
Q

What three categories can material be classified into?

A

Insulators
Conductors
Semiconductors

46
Q

Describe an insulator.

A

In an insulator, each electron is attached to an atom and cannot move away from the atom.

47
Q

What happens when a p.d. is applied across an insulator?

A

When a potential difference is applied across an insulator, no current passes through the material, because no electrons can move through the insulator.

48
Q

Describe a conductor.

A

In metals, most electrons are attached to atoms but some are delocalised. The delocalised electrons are the charge carriers.

49
Q

What happens when a p.d. is applied across a conductor?

A

The delocalised electrons are attracted towards the positive terminal of the metal.

50
Q

Describe a semiconductor.

A

In a semiconductor, the number of charge carriers increase with an increase of temperature.
The resistance of a semiconductor therefore decreases as the temperature is raised.

51
Q

What is an intrinsic semiconductor?

A

A pure semiconducting material is referred to as an intrinsic conductor, because conduction is due to electrons that break free from the atoms of the semiconductor.

52
Q

What is the law of charge forces?

A

Like charges repel.

Opposite charges attract.

53
Q

What happens to the charge carriers around a circuit, in terms of energy?

A

As the charge carrier leaves the cell, it passes through the components, transferring a fixed amount energy to the component.
After delivering the energy to the component, each charge carrier re-enters the cell and is resupplied with more energy to go around again and deliver to the component.

54
Q

What is the work done of the electron/charge carrier?

A

The work done of the electron is equal to its loss of energy.

55
Q

What happens when charge flows through a power source?

A

When a charge flows through a power source, it is raised through a potential, and energy is transferred to the charge as electrical potential energy.

56
Q

What is the difference between potential difference and electromotive force?

A

Potential difference is when the charge carrier loses energy. Energy is transferred to the components from the charge carriers.

Electromotive force is when the charge carrier gains energy. Energy is transferred from the power source to the charge carriers.

57
Q

Define electromotive force.

A

The emf of a source is defined as the electrical energy produced per unit charge passing through the source.

58
Q

What happens when current passes through a component with resistance?

A

The current has a heating effect when is passes through.

It also has a magnetic effect. which is made use of in electric motors and loudspeakers.

59
Q

What is the electrical power of a component?

A

The electrical power = current x potential difference.
P = I x V.
Power is in watts.

60
Q

What is the cause of resistance?

A

Resistance is caused by the repeated collisions between the charge carriers in the material with each other, and also between the charge carriers and the fixed positive ions of the material.

61
Q

What is a variable resistor?

A

A variable resistor/rheostat is used to adjust the current and potential difference as necessary.

A Level Physics for AQA. (25 decks)

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