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Physics - PAPER 2 > Electricity And Circuits > Flashcards

Electricity And Circuits Flashcards

1
Q

What happens when electricity is sent through a group 1 metal?

A

The electrons can be easily removed in Group 1.
So, the metal wire has many “free” electrons.
When a battery is attached to the wire, the voltage pushes the ‘free’ electrons around the circuit?

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2
Q

What is the direction of electrons in a circuit?

A

Go from negative terminal of the battery and are attracted to the positive terminal.

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3
Q

What is the direction of the conventional direction of current?

A

Goes from positive terminal to the negative terminal

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4
Q

What is a series circuit?

A

There is just one route the current can take around a circuit.
Can’t turn or turn off the lamps individually - if one fails, they all go off.

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5
Q

What is a parallel circuit?

A

There are junctions that allow the current to take different routes
Each lamp can be switched on or off separately

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6
Q

How is current measured?

A

Ammeter - measured in amps

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7
Q

How are ammeters placed in a circuit?

A

Placed in series

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8
Q

How is current conserved?

A

The total amount of current leaving the positive terminal is the same as the current arriving at the negative terminal

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9
Q

What is potential difference?

A

The difference in energy (carried by electrons) before and after they’ve flown through a component e.g. lamp

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10
Q

What is another name for potential difference?

A

Voltage

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11
Q

When will electrons flow?

A

When potential difference is applied

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12
Q

How is potential difference measured?

A

By voltmeter in volts

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13
Q

How do you calculate potential difference?

A

Potential difference = current x resistance

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15
Q

What is needed for a current to flow?

A

Closed circuit

Contain a source if potential difference e.g. cell or battery

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16
Q

How do you increase the current?

A

Increase potential difference

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17
Q

How are voltmeters places in a circuit?

A

In parallel in a circuit

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18
Q

What happens with potential difference in a parallel circuit?

A

The potential difference is the same across each branch

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19
Q

What happens if there is more than 1 component?

A

The potential difference across all components add up to give the total potential difference, supplied by cell/battery

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20
Q

What is charge measured in?

A

Coulombs (C)

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21
Q

What is electric current?

A

The rate of flow of charge

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22
Q

How do you calculate charge?

A

Charge = current x time

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23
Q

How is energy transferred in a circuit?

A

A cell/battery contains a store of energy

Energy is transferred into a charge

The charge can now transfer energy to the components in the circuit. It has potential energy.

Energy is transferred from the charge as it moves through the lamp

The lamp transfers energy to the surroundings by heating and by light

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24
Q

Why do some wires/components need a larger potential difference?

A

They need to produce a current as they have a large electrical resistance

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25
Q

What is resistance measured in?

A

Ohms

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26
Q

What happens when resistors are placed in a series circuit?

A

It’s harder for current to flow as the resistance of the circuit has increased.
The potential difference from the cell is shared but not equally as larger resistors need more potential difference

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27
Q

What happens when resistors are placed in a parallel circuit?

A

The total resistance is less than the resistance of each individual resistor
This is because there are more oaths for the current

28
Q

What are variable resistor sometimes used for?

A

To change the current in a circuit

29
Q

What happens when potential difference changes across a resistor?

A

The current changes at the same rate - directly proportional

So it’s just a straight linear line on graph

30
Q

What happens when potential difference increases in a lamp?

A

The current flows more which heats up the lamp
As the lamp gets warmer, the lamps resistance increases so as potential difference increases, current doesn’t.

Straight but curved over at top and bottom to show current has stopped increasing at same rate

31
Q

When happens with potential difference and resistance in a diode?

A

Low resistance if the potential difference is in one direction.
High resistance if potential difference is in the opposite direction

On graph the line will be low until it crosses y axis and shoot up

32
Q

What happens with a light-dependant resistor?

A

It has a high resistance in the dark (low light intensity) but resistance gets smaller when light intensity increases

Curve on graph gradually curves down but never hits axis

33
Q

What happens with thermistors and resistance?

A

They have high resistance at low temperature but resistance decreases when temperature increases.

The graph curves downward gradually.

34
Q

What is the Core Practical for Investigating Resistance?

A

1) Set up a circuit with 1 ammeter, 1 voltmeter and a resistor
2) Set power pack to lowest voltage and write readings off the ammeter and voltmeter
3) Repeat step 2) for different voltage settings
4) Replace the resistor with 2 filament lamps and repeat 2) and 3)

5) Set up a circuit with 3 voltmeters, 1 ammeter, and 2 filament lamps.
6) Repeat step 2)
7) Set up a circuit with 3 voltmeters, 3 ammeters and 2 lamps and repeat step 2)

35
Q

Why do circuits heat up?

A

All circuits have some resistance so the current heats the circuit up

36
Q

What happens when current passes through a resistor ?

A

Energy is transferred because electrical work has been done against the resistance

37
Q

Why does the resistor get warm?

A

Because energy is being transferred by heating

38
Q

Why is this heating effect useful?

A

Useful in a kettle or electric heater

39
Q

When is this heating effect not useful?

A

In computer or wires or plugs because it means useful energy is being waster/transferred as heat to the surroundings

40
Q

What happens inside a resistor?

A

As the electrons flow through the lattice of vibrating ions, they collide with the ions. The more collisions they make with the ions, the harder it is for them to pass through.
This is why electrical resistance increases
When the electrons collide with the ions, they transfer energy to them.

41
Q

How do you reduce resistance?

A

Reduced by using wires made from metals with low resistance e.g. copper
Thicker wires also have lower resistance
Therefore, resistance can be reduced by cooling metals so the lattice ions are not vibrating much.

42
Q

How do you calculate energy transferred (time)?

A

Energy = current x potential difference x time

Transferred

43
Q

How do you calculate power ( considering energy)?

A

Power = energy transferred / time taken

(W) (J) (S)

44
Q

How do you calculate electrical power (p.d.)?

A

Electrical power = current x potential difference

(W) (A) (V)

45
Q

How do you calculate electrical power (resistance)?

A

Electrical power = current (squared) x resistance

46
Q

What energy is transferred from a battery?

A

Some is transferred by electricity.
Some will be transferred as heating which heats the surrounding a little more

In a fan, the energy that is transferred by electricity is transferred as a store of kinetic energy to the fan

47
Q

What do appliances use that need a large amount of power?

A

Mains electricity (from national grid)

48
Q

What is a direct current?

A

When cells/batteries have a positive and negative terminal and the direction of the movement if charge, stays the same

49
Q

What is an alternating current?

A

Mains electricity is produced using generators that rotate which causes the direction of the current to keep changing

50
Q

What else changes in an alternating current?

A

Voltage - increases to a peak voltage, then decreases to zero. Which repeats

51
Q

What are the wires in a plug?

A

Earth wire - connects metal parts of appliance to a large spike that is pushed into ground
Neutral wire - the return path to the power station
Fuse
Live wire - connects the appliances to the generators at power station

52
Q

How are switches a safety feature?

A

They are connected to the live wire if a circuit so when the switch is off, no current goes through the appliance

53
Q

How is a fuse a safety feature?

A

A tube with a thin wire inside
The current passes through the wire and the wire gets hot.
If the current exceeds a certain temperature, the wire melts which breaks the circuit and stops the current.

54
Q

What do circuit breakers do?

A

They detect a change in current and safely switch off the supply

55
Q

Why is a circuit breaker better than a fuse?

A

Once a fault is fixed, they can be switch back on again.
Whereas a fuse has to be replaced each time

They work very quickly and can save lives
A fuse takes time to melt and won’t prevent you from getting a shock if you touch a live wire

56
Q

How do you calculate energy transferred?

A

Energy transferred = charge moved x potential difference

(J) (C) (V)

57
Q

Why are plastics insulators?

A

They collect the charge but don’t allow current to flow through them into other materials.
When the plastic rubs again something, it becomes negatively charged as it has gained electrons.

58
Q

What is the attraction between rods of opposite charge?

A

They attract each other

Same charge - repel each other

59
Q

How does a balloon cause static electricity? (Charging by induction)

A

1) The balloon has a negative charge
2) As the balloon is brought towards the wall, the electrons in the wall are repelled and moved away
3) The positive change left behind (induced charge) attracts the negative charge on the balloon

60
Q

How can static electricity be dangerous?

A

Can cause lightning - buildings have to have lightning conductors
Can cause electric shocks - electrons flow in whichever direction removed the excess charge (I.e. you) and you become discharge/earthed.
Can cause sparks - storage tanks for petrol and car tires are all earthed which makes them conducting

61
Q

What is a use of static electricity ?

A

Electrostatic spraying- sprayed on crops and the charged droplets spread out as they repel each other and are then attracted to the plant.
This means the spray spread around evenly (even underneath it) and less spray falls on ground (excess)

62
Q

What is a force field?

A

The volume of space around an object in which another object can experience a force

63
Q

What does a charged object have around it?

A

A force field called an electric field or electrostatic field

64
Q

What are the main points of field lines (in diagrams I.e. compass and magnets)

A

Never cross
Shows where the field is strongest (where lines are closer together)
Shows the direction of force on a charge in the field
Start on a positively charge object and end on the negative charged object

Physics - PAPER 2 (5 decks)

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