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Physixs > P3 > Flashcards

P3 Flashcards

1
Q

What is static electricity?

A

When two materials rub together, electrons are transferred from one to the other. If they are conductors, electrons flow in and out of them. But if they are insulators, electrons can’t flow and static electricity forms.

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2
Q

Which object becomes charged with positive static electricity?

A

The one which lost electrons.

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3
Q

Which object becomes charged with negative static electricity?

A

The one which gained electrons.

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4
Q

Which charges are the ones that move?

A

Negative charges (electrons)

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5
Q

How do electrically charged objects behave with each other?

A

They exert a force on one another. Things with opposite charges attract, and things with the same charges repel.

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6
Q

What are the forces between two charged objects known as?

A

Electrostatic attraction or repulsion.

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7
Q

How can you test to see if an object is electrically charged (scraps of paper and rod test)?

A

The paper “jumps” towards the rod. This happens because the rod induces a charge in the paper. If the rod is positive, it attracts the electrons in the paper towards it. If the rod is negative, it repels the electrons. This gives the surface of the paper an opposite charge to the rod, so they attract.

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8
Q

How can you test to see if an object is electrically charged (water and rod test)?

A

You can hold a rod near a stream of water. The rod induces a charge in the water, so the stream will be attracted to the rod and bend towards it.

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9
Q

How can you show the electric fields of a charged object?

A

Electric field lines, which always go from positive to negative and are always at a right angle to the surface of the object.

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10
Q

What does it mean if field lines are closer together?

A

The field is stronger, and the stronger the force a charged object in the field would experience.

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11
Q

What happens to the electric field lines when two oppositely charged objects interact?

A

The field lines “join up” and the objects are attracted to each other.

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12
Q

What happens to the electric field lines when two charged objects which are the same charge interact?

A

The field lines “push against” each other and the objects repel.

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13
Q

What is Current?

A

The rate of flow of electric charge around a circuit, measured in Amperes.

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14
Q

What conditions are necessary for Current to flow?

A

There must be a voltage across the component and the circuit must be complete.

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15
Q

What is Voltage (also known as Potential Difference)?

A

The driving force that pushes current around a circuit, measured in volts.

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16
Q

What is Resistance?

A

A measure of how easily charge can flow.

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17
Q

What is Charge?

A

The electrons which travel around a circuit, measured in coulombs.

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18
Q

How do you calculate Charge with Current and Time?

A

Charge (C) = Current (A) * Time (s)

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19
Q

How is voltage linked to energy transferred?

A

Voltage is the energy transferred per coulomb of charge that passes between two points in a circuit.

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20
Q

How can you calculate energy transferred using charge and voltage?

A

Energy transferred (J) = Charge (C) * Voltage (V)

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21
Q

What is a cell

A

c

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22
Q

What is a battery

A

Battery

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23
Q

What is an open switch

A

Open switch

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24
Q

What is a closed switch

A

Closed switch

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25
Q

What is a filament lamp

A

Filament lamp

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26
Q

What is an LED

A

LED

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27
Q

What are ‘Power supply terminals’

A

Power supply terminals

28
Q

What is a resistor

A

Resistor

29
Q

What is a variable resistor

A

Variable resistor

30
Q

What is an ammeter

A

Ammeter

31
Q

What is a voltmeter

A

Voltmeter

32
Q

What is a diode

A

Diode

33
Q

What is a LDR

A

LDR

34
Q

What is a thermistor

A

Thermistor

35
Q

What does an Ammeter do?

A

Measures the current (in amps) flowing through a component.

36
Q

Where must the Ammeter be placed in a circuit?

A

In series (in line with) the component.

37
Q

What does a Voltmeter do?

A

Measures the voltage (in volts) across the component.

38
Q

Where must the Voltmeter be placed in a circuit?

A

In parallel with the component being tested.

39
Q

How can you find voltage with current and resistance?

A

Voltage (V) = Current (A) * Resistance (ohms)

40
Q

resistor/wires graph

A

Resistor/wires graph - current is directly proportional to voltage.

41
Q

filament graph

A

Filament lamp graph - the increasing current increases the temperature of the filament which makes it resistance increase, so the graph is curved.

42
Q

diode graph

A

Diode graph - current only flows through in 1 direction. It has very high resistance in the other direction.

43
Q

Why does resistance increase with temperature?

A

As a resistor heats up, the particles start to vibrate more. With the particles moving around more it becomes more difficult for the electrons to get through the resistor.

44
Q

How does the amount of current affect resistance?

A

Most resistors have a limit to the current that can flow, as an increase in current means an increase in temperature.

45
Q

What is a diode?

A

A device made from a semiconductor material. It lets current flow freely through one direction, but has high resistance in the other direction.

46
Q

What is a LDR?

A

A LDR is a resistor dependent on the intensity of light. In darkness, the resistance is highest. As light increases, the resistance falls.

47
Q

Example of thermistor graph?

A

Thermistor graph - in constant conditions, the graph is curved. As current increases, the thermistor warms up and so resistance decreases.

48
Q

What is a sensing circuit?

A

They are used to turn on or increase the power to components depending on the conditions that they are in.

49
Q

How does a sensing circuit work (thermistor example)?

A

A fixed resistor and a fan are connected in parallel and therefore have the same voltage. The voltage of the power supply is shared between a thermistor and the parallel loop according to their resistances - the bigger the resistance, the more voltage a component receives. As a room gets hotter, the resistance of the thermistor decreases and the fan gets more voltage.

50
Q

What is a series circuit?

A

The different components are connected in a line, end to end. Current has to flow through all of the components to get around the circuit.

51
Q

What is a parallel circuit?

A

Each component is separately connected to the power supply, meaning that removing one component hardly affects others.

52
Q

How does voltage behave series circuits?

A

The voltage is shared between the various components - the voltage around a series circuit always adds up to the total voltage across the power supply.

53
Q

How does current behave in series circuits?

A

The same current flows through all parts of the circuit. The size of current is determined by total voltage and the total resistance.

54
Q

How does resistance behave in series circuits?

A

The total resistance is the sum of the individual resistances.

55
Q

What happens if you change the resistance of one component in a series circuit?

A

The voltage across all components changes too, as the amount of voltage a component receives depends on how difficult it is for energy to be transferred.

56
Q

How does voltage behave in parallel circuits?

A

It is the same across all branches of the circuit, the source voltage.

57
Q

How does current behave in parallel circuits?

A

The current is shared between each branch of the circuit. You can find the current in one branch by doing Voltage ÷ Resistance

58
Q

How do you calculate total resistance in a parallel circuit?

A

It’s difficult to work out - the total resistance of a parallel circuit is always less than that of a branch with the smallest resistance.

59
Q

How can you investigate the behaviour of voltage in series/parallel circuits?

A

Add bulbs to a circuit in series - the bulbs will get dimmer as the voltage is being spread and the current is falling as more resistance is added.

Add bulbs to a circuit in parallel - the bulbs will remain the same as the voltage across each branch is equal.

60
Q

Explain electric circuits/voltage in terms of energy and charges

A

Energy is supplied to the charge at the power source to “raise” it through a potential. The charge gives up this energy when it “falls” through a potential drop in components in the circuit.

61
Q

What is Power?

A

The power of a component tells you how much energy it transfers per second.

62
Q

What is a kilowatt-hour?

A

Measured in kWh, it is the amount of energy a device with a power of 1000 W transfers in 1 hour of operation.

63
Q

How do you calculate energy transferred with power and time?

A

Energy transferred (J) = Power (W) * Time (s)

64
Q

How do you calculate energy transferred with kilowatt-hours?

A

Energy transferred (J) = Power (kW) * Time (h)

65
Q

How do you calculate power with voltage and current?

A

Power (W) = Voltage (V) * Current (A)

66
Q

How do you calculate power with current and resistance?

A

Power = Current² (A)² * Resistance (ohms)

Physixs (8 decks)

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