Topic Two - Electricity Flashcards

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1
Q

What is the current in a single closed loop circuit?

A

The current has the same value everywhere.

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2
Q

What is potential difference?

A

The driving force that pushes the charge around.

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3
Q

What is resistance?

A

Anything in the curcuit that slows the flow down.

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4
Q

What is the unit of current?

A

amps.

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5
Q

What is the unit of potential difference?

A

Volts.

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6
Q

What is the unit of resistance?

A

Ohms.

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7
Q

What happens if their is a greater resistance in the component?

A

The grater the resistance across a component the smaller the current that flows through it.

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8
Q

What is charge measured in?

A

Coulombs.

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9
Q

What is time measured in for the charge equation?

A

Seconds.

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10
Q

What happens to the reistance of an ohmic conductor? ( wire or resistor ).

A

It doesnt change with the current if it is at a constant temperature the current through a ohmic conductor is directly proportional to the potential difference across it.

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11
Q

What happenes to the resistance of a filament lamp?

A

The electric chanrge of a filament lamp transfers some energy to the thermal energy store of the filament which heats up. Resistance increases with temperature so as the current increases the lamp heats up more and the resistance increases.

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12
Q

What happens to the resistance in diodes?

A

It depends on the direction of the current. If the flow of the current is reversed the resistance will be very high.

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13
Q

What must the ammeter be in the resistance practical?

A

In series with whatever yor investigating.

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14
Q

Where must the volmeter be in the resistance practical?

A

In parallel around what your not investigating.

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15
Q

What is the method for the investigating resistance practical?

A
  • attach a crocodile clip to the wire level with 0cm on the ruler.
  • attach a second crocodile clip to the wire at a different length along the ruler and write down the length between the clips.
  • close the switch and record the current and potential difference across it.
  • open the second crocodile clip and move it further along the wire then close the switch measure the distance between, current and potential difference.
  • repeat this for diferent lengths of the test wire.
  • use the measurements to calculate the resistance for each length of wire.
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16
Q

What is the relationship between length and resistance?

A

Directly proportional.

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17
Q

Why may the graph for the resistance practical not go through the origin?

A

The first clip may not be attached at exactly zero so all readings are abit out it is a systematic error.

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18
Q

What does the ammeter measure?

A

Current.

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19
Q

What does the voltmeter measure?

A

Potential difference.

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20
Q

What type of wire will give you the best results for the resistance practical?

A

A thin wire and make sure its straight.

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21
Q

What might effect the resistance in the resistance practical?

A

The wire may heat up so leave the switch open between readings to let the circuit cool down.

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22
Q

What is the practical investigating i-v characteristics?

A
  • set up test circuit.
  • vary the variable resistor which alters the current flowing through and the potential difference across the component.
  • take several readings from the ammeter and voltmeter to see how the potential difference varies and the current changes.
  • repeat each reading twice to get an average of each current.
  • swap the wires connected to the cell so the current direction is reversed.
  • plot a grah of current against voltage for the component.
23
Q

What is an LDR?

A

Light dependant resistor meaning it is dependant if the intensity of the light.

24
Q

What happens to the resistance of the LDR in the dark?

A

The resistance is at its highest.

25
Q

What is a thermistor?

A

A temperature dependant resistor.

26
Q

What happened to the resistance of a thermistor in hot conditions?

A

The resistance lowers.

27
Q

What happens to the resistance of the thermistor in cool conditions?

A

The resistance goes up.

28
Q

What are sensing circuits used for?

A

They can be used to increase the power to components depending on the conditions that they are in.

29
Q

What happens to components connected in series?

A

There is the same current through each component.
The total potential difference of the power supply is shared between the components.
The total resistance of two components is the sum of the resistance of each component.

30
Q

What happens to components connected in parallel?

A

The potential difference across each component is the same.
The total current through the whole circuit is the sum of the currents through the separate components.
If you have two resistors in parallel the total resistance is less than the resistance of the smallest of the two resistors.

31
Q

Describe the investigation of adding resistors in series.

A

You will need at least 4 identical resistors.
Then build a circuit using one resistor, an ammeter, and a battery (take note of the betterys potential difference).
Measure the current using the ammeter and calculate the resistance of the circuit.
Repeat until you have added all of your resistors.
Plot a graph of the number of resistors against the total resistance of the circuit.

32
Q

Describe the investigation of adding resistors in parallel.

A

Using the same equipment as you did in the series investigation build the same circuit.
Measure the total current through the cicuit and calculate the resistnace.
Add another resistor in parallel with the first.
Measure the total current through and the potential difference to calculate the overall resistance.
Repeat until you have added all your resistors.
Plot a graph of the number of resistors against the total resistance.

33
Q

What are the two types of electricity supplies?

A

Alternating current and direct current.

34
Q

What is the ac supply in the Uk mains supply?

A

230V.

35
Q

What is the frequency of the Uk mains supply?

A

50Hz.

36
Q

What is alternating current?

A

Where the current is constantly changing direction and the positive and negative ends keep alternating.

37
Q

What is direct current?

A

Current always flowing in the same direction.

38
Q

What are most electrical appliances connencted to the mains supply by?

A

Three core cables with three wires inside them each with a core of copper and plastic coating.

39
Q

What colour is the live wire?

A

Brown.

40
Q

What does the live wire do?

A

Provides the alternating potential difference from the mains supply at about 230V.

41
Q

What colour is the earth wire?

A

Green and yellow.

42
Q

What does the earth wire do?

A

It is for protecting the wiring and for safety as it stops the appliance becoming live. It doesnt usually carry current only when there is a fault, it is 0V.

43
Q

What colour is the neutral wire?

A

Blue.

44
Q

What does the neutral wire do?

A

Completed the circuit and carries away current. Electricity normally flows in through the live wire and out through the neutral wire. 0V.

45
Q

How does a live wire give us an electric shock?

A

Your body is at 0V so if you touch a live wire a large potential difference is produced and a current flows through you, which causes electric shock.

46
Q

How are turned off circuits still dangerous?

A

There is still a danger of electric shock as current is flowing but there is still potential difference in the live wire. So if you make contact with the live wire your body would provide a link between the supply and the earth so a current would flow through you.

47
Q

How are connection between live and earth dangerous?

A

App connections between live and earth are dangerous as it creates a low resistance path to earth and a huge current will flow which could result in fire.

48
Q

How does a kettle transfer energy?

A

Transfers energy electrically for the mains ac supply to the thermal energy store of the heating element insife the kettle.

49
Q

How does a fan transfer energy?

A

Energy is transferred electrically from the battery of a handheld fan to the kinetic energy store of the fans motor.

50
Q

Who does the amount of energy transferred depend on its power?

A

It depends on how long its on for and its power as the power of the appliance is the energy transferred per second.

51
Q

What is the national grid?

A

It is a giant system of cables and transformers they covers the uk and connects power stations to consumers.

52
Q

How does the national grid produce alot of power?

A

They create a really high potential difference and keep the current low. This is because the problem with a high current is thay you lose lots of energy and the wires hest up and energy is transferred to the thermal energy store of he surroundings.

53
Q

How does the national grid work?

A

It uses transformers as well as big pylons with hige insulators. The potential difference is stepped up using a step up transformer. It is then stepped down for domestic use using a step down transformer. Transformers are almost 100% efficient so input power is equal to output power.