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Physics Paper 1 > Electricity > Flashcards

Electricity Flashcards

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1
Q

What is the Function of the Filament Lamp in a Circuit

A

An electrical current heats the filament in a bulb so that it gives out light.

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2
Q

What is the Function of the LED in a Circuit

A

A LED signals/ allows one way current.

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3
Q

What is the Function of the Switch in a Circuit

A

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

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4
Q

What is the Function of the Fuse in a Circuit

A

A fuse melts/ breaks when the current becomes too high

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5
Q

What is the Function of the Cells and Batteries in a Circuit

A

-Cells and batteries provide energy to the charged particles to push them around a circuit.

-A battery is two or more cells.

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6
Q

What is the Function of the Ammeter and Voltmeter in a Circuit

A

-An ammeter measures the current in a circuit. It is addend in series in a circuit.

-A voltmeter measures the potential difference (voltage) in a circuit. It is added in parallel in a circuit.

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7
Q

What is the Function of the Fixed Resistor in a Circuit

A

-A resistor restricts or limits the flow of electrical current.

-A fixed resistor has a resistance that does not change.

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8
Q

What is the Function of the Variable Resistor in a Circuit

A

-Moving the position of the slider on this resistor, changes the resistance.

-This allows the current to be varied.

-A variable resistor is used in some dimmer switches and volume controls.

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9
Q

What is the Function of the Thermistor in a Circuit

A

-The resistance of a thermistor depends on its temperature.

-At low temperatures, the thermistor has a high resistance.

-As the temperature increases, the resistance decreases.

-A thermistor can be used in thermostats or heat activated fire alarms.

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10
Q

What is the Function of the Light Dependant Resistor (LDR) in a Circuit

A

-The resistance of a LDR depends on light intensity.

-At low light levels, the LDR has a high resistance.

-As the light intensity increases, the resistance decreases.

-A LDR can be used as a sensor in cameras or automatic lights that come on when it gets dark.

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11
Q

What is the Function of the Diode in a Circuit

A

-A diode allows current to flow in one direction only. Current will not flow in the other direction.

-Diodes are used to convert an alternating current into a direct current.

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12
Q

What is meant by Charge

A

-Charge is a property of a body which experiences a force in an electric field.

-Electrons are negatively charged particles that transfer energy through wires as electricity.

-The movement of electrons is the charge flow.

-Charge is measured in Coulombs (C)

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13
Q

What is the Equation for Charge Flow

A

Charge Flow (C) = Current (A) x Time (s)

Q= It

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14
Q

What is meant by an Electrical Current

A

-A current is the rate of flow of electric charge around a circuit.

-The electrons flow from the negative pole of the cell to the positive pole of the cell (conventional current).

-It is measured in Amps, A on an Ammeter.

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15
Q

What is meant by the Energy Transfer by Components

A

When a charge moves through a component with a potential difference, electrical work is done and energy transferred.

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16
Q

What is the Calculation for Energy Transfer by Components

A

Energy Transferred (J) = Charge Flow (C) x Potential Difference (V)

E= QV

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17
Q

What is meant by Potential Difference

A

-The cell has a store of chemical energy. The energy is carried around the circuit by electrons.

-When the electrons pass through components, some of the energy is transferred to other forms of energy for example light and thermal energy.

-The potential difference across a component gives us an
idea of the energy transferred by the component

-It is measured in Volts, V on a voltmeter.

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18
Q

What is the Calculation for Potential Difference

A

Potential Difference (V) = Current (A) x Resistance (Ω)

V= IR

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19
Q

What is meant by Resistance

A

-An electrical current is a flow of electrons around a circuit. These carry energy.

-When the electrons pass through a component they collide with atoms in the metal. The energy is transferred to thermal energy.

-The resistance tells us the potential difference required to drive one coulomb of charge through. The unit for resistance is the ohm (Ω).

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20
Q

What is Ohm’s Law

A

-Ohm’s law says that current is proportional to potential difference in an ohmic conductor.

-This means resistance stays constant which only happens at a constant temperature.

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21
Q

What is meant by a Series Circuit

A

-A series circuit is a circuit where all of the components are connected to a single loop.

-Electrons only have one path to follow so form one current. The current has to flow through every component.

-This means if one of the bulbs is broken then current will not be able to flow round the circuit. If one bulb goes out, they all go out.

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22
Q

Explain why Electrical Current Causes the Lamp to Light Up

A

-Electrons only have one path to follow so form one current.

-The electrons in an electric current are carrying energy.

-In the filament lamp, some of this energy is
transferred into thermal energy and light.

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23
Q

Describe the Current in a Series Circuit

A

-In a series circuit, the electrons only have one path to follow. This means the current will be the same all the way around the circuit.

-Ammeter 1 = Ammeter 2 = Ammeter 3

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24
Q

Describe the Potential Difference in a Series Circuit

A

-The current will transfer energy from the power supply to the components in the circuit.

-Since energy has to be conserved, all of the source energy is shared between the components.

-Since potential difference is used to measure changes in energy, the potential difference supplied is equal to the total of the potential differences across all other
components.

-Voltmeter 1 = Voltmeter 2 + Voltmeter 3

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25
Q

Describe the Resistance in a Series Circuit

A

-If resistors are connected in series, the current must flow through both of them meaning the resistances are added together.

-Total Resistance = Resistor 1 + Resistor 2 +…

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26
Q

What is meant by a Parallel Circuit

A

-A parallel circuit is a circuit where all of the components are connected to two or more loops.

-Electrons have multiple paths to follow. An electron will not pass through every component on its way round the circuit.

-If one of the bulbs is broken then current will still be able to flow round the circuit through the other loop. If one bulb goes out, the other will stay on.

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27
Q

Describe the Current in a Parallel Circuit

A

-Since there are different loops, the current will split as it leaves the cell and pass through one or other of the loops.

-This means the current in a parallel circuit is not the same all around the circuit.

-Ammeter 1 = Ammeter 2 + Ammeter 3

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28
Q

Describe the Potential Difference in a Parallel Circuit

A

-Since energy has to be conserved, the energy transferred around the circuit by the electrons is the same whichever path the electrons follow.

-Since potential difference is used to measure changes in energy, the potential difference supplied is equal to the potential differences across each of the parallel components.

-Voltmeter 1 = Voltmeter 2 = Voltmeter 3

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29
Q

Describe the Resistance in a Parallel Circuit

A

-If resistors are connected in parallel, the supply current is divided between them.

-The overall resistance is reduced as the current may follow multiple paths.

-(It gives another path for charge to flow).

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30
Q

Describe two Differences Between Series and Parallel Circuits

A

-In a parallel circuit, there are branches. In a series circuit, there are no branches.

-In a parallel circuit, the current splits between the different branches. This means that the current in a parallel circuit is not the same all around the circuit.

-In a series circuit, the current cannot split so the current is the same all around a series circuit.

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31
Q

Describe the Potential Difference in Batteries

A

-In batteries, the potential difference of each cell is added together to reach the potential difference of the battery.

-If the cells are facing opposite directions, then their potential differences will cancel out so the battery’s potential difference will be 0 Volts.

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32
Q

Describe the I-V Graph of Fixed Resistors

A

-The gradient is constant. This means the resistance is constant.

-If we increase the potential difference across a resistor and measure the current, then we get a straight line passing through zero.

-This shows that current and potential difference are directly proportional. This means that a fixed resistor is in Ohmic conductor.

33
Q

Explain why a Filament Glows when a Current is Running Through It

A

-A filament is a very thin wire. These have a very high resistance.

-Because the filament is so thin, it has a high resistance. This means that the potential difference across the resistor is very high.

Because the potential difference is so high, a great deal of energy is transferred to thermal energy in the filament. The temperature of the filament increases until it glows.

34
Q

Describe the I-V Graph of Filament Bulbs

A

-The gradient is curved at the edges. This means the resistance is not constant.

-If we increase the potential difference across a filament lamp then we increase the current. However, at a high potential difference, the current no longer increases by the same amount.

-This shows that the current and potential difference are not directly proportional. This means a filament bulb is a Non-ohmic conductor.

35
Q

Explain why the Resistance of the Filament Increases as it Gets Hot.

A

-In order for an electrical current to pass through a conductor, the delocalised electrons must move from the negative end to the positive end.

-Under cool conditions, the metal atoms are not vibrating
strongly so the delocalised electrons can easily pass through the metal.

-However, as the temperature of the metal increases, the metal atoms vibrate much more strongly.

-Now it requires more energy (ie greater potential difference) for the delocalised electrons to pass through the metal.

-Because we now need a greater potential difference to achieve the same current, we can see that the resistance of the wire increases at higher temperatures.

36
Q

Describe the I-V Graph of Diodes

A

-The current is in one direction so only curves at one end.

-The current and potential difference are not directly proportional.

-This means a diode is a Non-ohmic conductor.

37
Q

Describe a Similarity and Difference between a Normal Diode and a Light Emitting Diode (LED)

A

Similarity: both the normal diode and the light-emitting diode will only allow current to flow in one direction around a circuit (the conventional current must be in the direction of the arrow shown on the symbol).

Difference: the light-emitting diode emits light when a current flows through it. A normal diode does not do this.

38
Q

Describe the Advantages of using an Light Emitting Diode (LED) in a Circuit Rather than a Filament Lamp

A

-A LED is much more energy-efficient than a filament lamp. In a filament lamp, most of the energy is transferred to thermal (heat) energy with only a small proportion transferred to light.

-However, with an LED, a much greater proportion of the energy is transferred to light and only a tiny proportion transferred to thermal energy.

-This means that a much smaller amount of energy is required to achieve the same light level using an LED compared to a filament lamp.

-A filament lamp emits a great deal of thermal energy. If a circuit contains several filament lamps, there is a risk that the circuit will overheat. This is not a risk with LEDs as they transfer only a tiny amount of energy to thermal energy.

39
Q

Describe how the Resistance of a Light Dependant Resistor (LDR) Varies with Light Intensity.

A

-As the light intensity increases, the resistance of the LDR decreases.

-As the light intensity decreases, the resistance of the LDR increases.

-This means that an LDR has a huge resistance in the dark and a very low resistance in the light.

-They are used in cameras, street lights and phone screens.

40
Q

Describe how the Resistance of a Thermistor Varies with Temperature.

A

-As the temperature increases, the resistance of the thermistor decreases.

-As the temperature decreases, the resistance of the thermistor increases.

-This means that an thermistor has a huge resistance at low temperatures and a very low resistance at high temperatures.

-They are used in kettles, thermostats, and smoke detectors.

41
Q

Explain how a Thermistor Determines whether a Bulb will Turn On in Different Temperatures

A

-Because the resistance of the thermistor is high, the majority of the potential difference is now across the thermistor.

-This means that the potential difference across the bulb is low so the bulb is turned off.

-In hot conditions, the resistance of the thermistor falls to a low value. Now the potential difference across the thermistor is low.

-This means that the majority of the potential difference is across the fan, so the fan is switched on, cooling the computer.

42
Q

Explain how a Thermistor is Used in Incubators for Premature Babies

A

-Premature babies are often much smaller than full-term babies. This means that premature babies lose body heat quickly. To prevent this, premature babies are usually kept in a temperature controlled incubator.

-The incubator contains a thermistor (in a thermostat). The temperature of the incubator is set by the medical team and this is then maintained by the thermostat.

-However, as this is a life-critical system, there will also be back-up systems and an alarm, in case there is a problem and the temperature is not controlled properly.

43
Q

Describe the Different Factors Affecting Resistance

A

Material- copper has a lower resistance than steel due to the different size and shape of their ions.

Length- longer wires have greater resistance as there is more chance of collisions with ions.

Temperature- heating a wire increases its resistance as the ions will have more energy and so be will be moving more causing more collisions.

Diameter- smaller diameter wires have greater resistance as there is less space so ions will collide more.

44
Q

Describe a Method for the Resistance Required Practical

A

-Set up a circuit with a cell, ammeter and voltmeter. Connect this with crocodile clips to a thin resistance wire attached to a metre ruler. Place the clips 100cm apart.

-Record the reading on the ammeter and the voltmeter.

-Move one of the crocodile clips closer until they are 90 cm apart. Record the new readings on the ammeter and the voltmeter.

-Repeat the previous steps reducing the length of the wire by 10 cm each time down to a minimum length of 10 cm.

-Use the results to calculate the resistance of each length of wire by using R = V / I. Plot a graph of resistance against length for the resistance wire.

45
Q

Evaluate the Results in the Resistance Required Practical

A

-The longer the piece of wire, the higher the resistance.

-Resistance is directly proportional to length as the graph gives a straight line through the origin.

46
Q

Why should the Minimum Length of Wire be 10cm in the Resistance Required Practical

A

-In this practical, we should not get any value for the resistance when the crocodile clip is set to a length of zero (that’s because there should be no wire for there to be any resistance in).

-However, what we find is that there is a resistance. This is due to two effects.

-Firstly, it is impossible to connect the two crocodile clips with no wire between them. That is because crocodile clips are quite large.

-Secondly, there is always resistance where the crocodile clip touches the wire. This is called contact resistance.

47
Q

Explain why the Wire Getting Warm will be a Problem in the Resistance Required Practical

A

-If the temperature of the wire increases, then the resistance of the wire will also increase.

-This means the wire will no longer be an ohmic conductor.

48
Q

Suggest Solutions to Reduce the Problem of the Wire Heating in the Resistance Required Practical

A

-If we use a high potential difference, then more energy is transferred to thermal energy in the wire, compared to using a low potential difference.

-Because we do not want the wire to increase in temperature, it is best to use a low potential difference.

-Turn off the current in between readings. If we leave the current running, then the wire will increase in temperature, affecting the final results.

49
Q

Describe a Method for the I-V Characteristics Required Practical

A
  1. Set up a circuit with a cell, ammeter, voltmeter, fixed resistor and variable resistor.
  2. Ensure that the power supply is set to zero at the start.
  3. Record the reading on the voltmeter and ammeter.
  4. Use the variable resistor to alter the potential difference.
    Record the new readings on the voltmeter and ammeter.
  5. Repeat steps three to four, each time increasing the potential difference slightly.
  6. Reverse the power supply connections and repeat steps two to five.
  7. Plot a graph of current against potential difference for each component. Repeat the experiment but replace the fixed resistor with a bulb and then a diode.
50
Q

Describe how Resistance can be Calculated Using the Circuit in the I-V Characteristics Required Practical

A

-Switch on the circuit.

-Read both the ammeter and voltmeter.

-Adjust the variable resistor to change the current.

-Take further readings from the meters.

-Draw of Graph of V against I

-Use the calculation R = V / I to calculate the resistance and draw the gradient.

51
Q

Why is it Important to not keep the Circuit Connected for too long in the I-V Characteristics Required Practical

A

-Tt is very important that the temperature across a fixed resistor remains constant.

-If the temperature changes, then the current will no longer be directly proportional to the potential difference. The resistor will no longer be an ohmic conductor.

-If the circuit is connected for too long, then the temperature of the resistor will increase. The current will no longer be directly proportional to the potential difference. In other words, it will no longer be an ohmic
conductor.

52
Q

Describe the Conclusion of the I-V Characteristics Practical for a Fixed Resistor

A

-In a fixed resistor, as the potential difference increases so does the current.

-This means the resistance stays the same.

53
Q

Describe the Conclusion of the I-V Characteristics Practical for a Filament Bulb

A

-In a filament bulb, as the current increases so does the temperature.

-This causes the resistance to increases.

-This is because ions in the filament vibrate more when heated making it harder for electrons to flow past.

54
Q

Describe the Conclusion of the I-V Characteristics Practical for a Diode

A

-In a diode, increasing the current in the forwards direction causes the resistance to increase also.

-In the reverse direction, the resistance is so high that current cannot flow.

-This means current can only flow in one direction.

55
Q

Give a Risk Assessment for the Resistance and I-V Characteristics Required Practicals

A

Hazard- Heating of the resistance wire

Risk- Burns to the skin

Solution- Do not touch the resistance wire whilst the circuit is connected. Allow the wire time to cool.

56
Q

Explain what Causes Heating in Wires

A

-As electrons flow through wires, they collide with the
ions in the wire which causes the ions to vibrate more.

-This increased vibration of the ions increases the temperature of the wire.

-Energy has been transferred from the chemical energy store of the battery into the internal energy store of the wire

57
Q

What is meant by Energy Transfer by Appliances

A

-When electrical appliances are at work, they transfer energy from one store to another.

-When any appliance transfers energy to the kinetic energy store, there will always be a small amount transferred to the thermal energy store as well.

-This is due to friction and it is very hard to avoid. However, this is not the intended energy transfer for that appliance so we don’t consider this.

58
Q

What is the Calculation for Efficiency

A

Efficiency = (Useful Output Energy Transfer / Total Input Energy Transfer) x100

Efficiency = (Useful Power Output / Total Power Input) x100

59
Q

Explain why a Clothes Dryer has a much Higher Power rating than a Fan

A

-In a fan, the main energy transfer is to the kinetic energy store. There will be a tiny amount of energy transfer to the thermal energy store (due to friction) but this is not the intended energy transfer.

-This means that a fan only transfers a relatively small amount of energy each second, so it has a relatively low power rating.

-A clothes dryer has a much greater power rating than the fan. This is because there are two intended energy transfers.

-Firstly, the clothes dryer transfers energy to the kinetic energy store to turn the rotating drum (and the clothes inside). Secondly, the clothes dryer has to heat the air to dry the clothes. This involves transferring a lot of energy to the thermal energy store.

-Due to both of these energy transfers, the clothes dryer transfers a large amount of energy each second so it has a high power rating.

60
Q

What is the Calculation for Energy Transfer by Appliances

A

Energy Transferred (J) = Power (W) x Time (s)

E= Pt

61
Q

What are the Calculations for Power of Components

A

Power (W) = Potential Difference (V) x Current (A)

P= VI

Power (W) = Current² (A) x Resistance (Ω)

P= I²R

62
Q

Describe the Difference between Alternating Current (A.C.) and Direct Current (D.C.)

A

-The electrical supply from a cell is an example of direct current. This is because the current moves in one direction only and the potential difference does not change.

-Mains electricity is an alternating current. With AC, the current switches direction many times every second and the potential difference rises and falls.

-The benefit of AC is that we can use a transformer to easily change the potential difference of the supply. Mains electricity has a frequency of 50 Hz and a potential difference of around 230 V.

63
Q

What is the Calculation for Frequency

A

-Frequency is the number of cycles per second

-Frequency (Hz) = 1 / time period

-The time period is the time taken for a full cycle

64
Q

Describe the Purposes of the Wires in a Plug

A

-The Live wire is brown. It carries an alternating current from the generators. this wire can be dangerous even if a switch in the mains circuit is open.

-The Neutral wire is blue. Its purpose is to complete the circuit.

-The Earth wire is green and yellow. This wire is held at 0V. If there is a fault so the casing of the appliance becomes live, this wire carries current to the Earth. This causes the fuse to melt, shutting off the current.

65
Q

Explain why the Wires in a Plug are made of Copper

A

The wires in three-core cable are made of copper as copper is an extremely good conductor of electricity.

66
Q

Explain why the Wires in a Plug are Coated by Plastic

A

-The wires are coated with plastic. This is because plastic does not conduct electricity.

-If the wires were not coated with plastic, an electric current would simply flow from the live wire to the neutral and the Earth wires.

-A huge current would flow and this would be seriously dangerous.

67
Q

Explain why the Live Wire can be Dangerous even if the Switch is Open

A

-The live wire is always carrying an electrical current.

-If the switch is open, then the live wire before the switch is carrying an electrical current.

-If a person touched the live wire before the switch, they would receive an electric shock which could be fatal.

68
Q

Explain why the Neutral Wire cannot carry a Current if the Switch is Open

A

-The neutral wire only carries an electrical current if it is connected to the live wire as it completes the circuit.

-If the switch is open, then the neutral wire is not connected to the live wire, so it will not be carrying an electrical current.

69
Q

Explain how the Earth Wire and the Fuse act together to Prevent Electrocution

A

-If a fault develops so that the live wire is touching the case, the case now becomes live. It is now carrying an electrical current. If someone touched the case, they could receive an electrical shock.

-Appliances are connected to the Earth wire. This means that the metal case of the appliance has a wire running from the case straight down into the Earth.

-Now, if a fault develops and the case becomes live, this causes a massive electrical current to run straight down the Earth wire to the Earth.

-The fuse is designed so that if a large current runs through it, then the fuse melts and shuts down the current.

-So in the case of the fault, because a huge current is now running down to Earth, the fuse melts and the current stops. This means that the appliance is safe.

70
Q

What is the National Grid

A

The National Grid is a network of transformers and high-voltage cables.

-It connects power stations to peoples homes

71
Q

Describe how the National Grid Works

A

-Electricity has to be transmitted from power stations to homes, offices and factories. The problem is that a lot of energy is lost in the transmission cables.

-One way to reduce this is to transmit the electricity at very high potential difference. This reduces the resistance in wires as the current is low so less energy is lost.

-First the electricity passes through step-up transformers which increase the potential difference from 25,000 to 400,000 volts. The electricity then passes through high voltage cables.

-Finally, step-down transformers decrease the potential difference to 230 volts so that it is safer before the electricity is passed to homes.

72
Q

Explain why Electricity is Transmitted Using a High Potential Difference rather than a High Current

A

-To transmit the huge amount of power needed, you need either a high potential difference or a high current.

-The problem with a high current is that lots of energy is lost as the wires heat up and energy is transferred to the thermal energy store of the surroundings.

-It is much cheaper to increase the potential difference to a very high amount (400,000 V) and keep the current as low as possible.

-For a given power, increasing the potential difference decreases the current which decreases the energy lost by heating to the wires and the surroundings.

-This makes the national grid an efficient way of transferring electricity.

73
Q

What is meant by Static Electricity

A

Static electricity is the build up of charge on insulating materials (caused by friction).

74
Q

Explain how friction can charge Materials

A

-When insulating materials rub against each other, they may become electrically charged.

-Electrons, which are negatively charged, may be ‘rubbed off’ one material and on to the other.

-The material that gains electrons becomes negatively charged.

-The material that loses electrons is left with a positive charge.

75
Q

Explain, in terms of Electrons, what happens when a Polythene Rod is Rubbed with a Duster

A

-When a polythene rod is rubbed with a duster, the
friction causes electrons to gain energy.

-Electrons gain enough energy to leave the atom and ‘rub off’ onto the polythene rod.

-The polythene rod has gained electrons, giving it a negative charge

-The duster has lost electrons, giving it a positive charge

76
Q

Explain, in terms of Electrons, what happens when Insulators are Rubbed together Compared to Conductors

A

-Insulators prevent the electrons from moving and the charge remains static.

-Conductors, on the other hand, cannot hold the charge, as the electrons can move through them.

77
Q

Why is Static Electricity Dangerous when Refuelling an Aeroplane

A

-Static electricity is dangerous when refuelling an aeroplane because a build up of charge can cause a spark which can ignite the fuel, causing an explosion.

-To prevent this, both the refuelling truck and airplane are Earthed. This means that no charges or a potential difference can develop so no sparking takes place.

78
Q

Explain what will happen when two Like Charges are together compared to Opposite Charges

A

-If two objects have the same type of charge, they will experience a force of repulsion and move further apart.

-If two objects have different charges, they will experience a force of attraction and will move closer together.

79
Q

Explain how Sparks are Caused

A

-Sparks are caused when there is a high enough potential difference between a charged object and an earthed object.

-A high potential difference causes a strong electric field between the charged object and the earthed object.

-The strong electric field causes electrons in the air particles to be removed (ionisation)

-Air is normally an insulator but when it is ionised, it is much more conductive, so a current can flow through it. This is the spark.

Physics Paper 1 (4 decks)

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