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BMAT > BMAT Physics - Electricity > Flashcards

BMAT Physics - Electricity Flashcards

1
Q

What is an electrostatic conductor?

A

A material that can disperse electrons easily.

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2
Q

What is an electrostatic insulator?

A

A material that cannot disperse electrons easily.

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3
Q

What is static electricity?

A

1) When two electrostatic insulators are rubbed together i.e. friction, there is a of flow of charge from one insulator to the other.
2) The insulator that loses electrons becomes positively charged.
3) The insulator that gains electrons becomes negatively charged.

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4
Q

Objects with the same charge…

A

…repel

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5
Q

Objects with the opposite charge…

A

…attract

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6
Q

How else can objects be charged?

A

Induction

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7
Q

What is induction?

A

1) Placing a neutral object next to charged objects causes it to become charged.
2) If one end of this newly charged object is momentarily earthed, the object becomes permanently charged.

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8
Q

Application of static electricity?

A

Spray paint:

  • The object to be painted and the paint both have opposite charges.
  • This means they are attracted to each other.
  • Therefore less paint is wasted.
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9
Q

Why is static electricity dangerous?

A

Sparks can form upon spontaneous dissipation of electrical charge which can lead to fire.

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10
Q

What can be used to reduce the risk of a spark?

A

Earthing of objects that can build up too much charge.

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11
Q

Draw the circuit symbols for:

  • cell
  • ac supply
  • variable resistor
  • fixed resistor
  • ammeter
  • diode
  • voltmeter
  • switch
  • thermistor
  • batteries
  • wires connected
  • wires not connected
  • light dependent resistor (LDR)
A

Look at notes

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12
Q

What is an alternate current?

A

Current that repeatedly changes direction - supplied from power station generators and the mains.

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13
Q

What is direct current?

A

Current that is always supplied in the same direction - supplied from batteries and cells.

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14
Q

Describe alternating current.

A

The current changes direction at a certain regular frequency which produces a waveform.

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15
Q

What frequency is the main current supplied at in the UK?

A

50Hz (50 oscillations per second)

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16
Q

What is current?

A

Current is the rate of flow of charge/charged particles through an electrical conductor.

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17
Q

Current, Charge, Time equation?

A 
Current = Charge/time
I = Q/t
A = C/s
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18
Q

What is current measured in?

What is current measured using?

A

Current is measured in Amperes (A). It is measured using an ammeter.

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19
Q

How is an ammeter placed in a circuit?

A

An ammeter is always placed in series with the components in a circuit.

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20
Q

What is potential difference?

A

Potential difference is the work done to move charge between two points.

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21
Q

What is potential difference measured in? What is potential difference measured using?

A

Potential difference is measured in volts. It is measured using a voltmeter.

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22
Q

Potential difference, work done, charge equation?

A

Potential difference = work done / charge
V = W/Q
V = J/C

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23
Q

1V is….

A

…the work done to move one coloumb of charge between two points.

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24
Q

1A is…

A

…the current that flows when 1C of charge flows in the circuit each second.

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25
Q

How is a voltmeter placed in a circuit?

A

A voltmeter is always placed in parallel with the component in the circuit, whose potential difference you are trying to measure.

26
Q

What is resistance?

A

Resistance is the opposition to the flow of current in a circuit.

27
Q

All conductors carry a certain resistance. What is the resistance directly proportional to and inversely proportional to?

A

Current is directly proportional to the length of the conductor and inversely proportional to the cross-sectional area.

28
Q

Resistance, current, potential difference equation?

A 
Resistance = Potential difference/ Current
R = V/I
Ohms = V/A
29
Q

What is resistance measured in?

A

Resistance is measured in ohms.

30
Q

1 ohms is…

A

..the resistance of a conductor when a potential difference of 1V produces a current of 1A

31
Q

Describe the current-potential difference graph for a resistor?

A
  • Produces a straigth line graph through the origin.
  • Current is directly proportional to the resistance.
  • Constant gradient indicates constant resistance for different values of current.
32
Q

How can you calculate the resistance from a current-potential difference graph?

A

1 / gradient of the line = resistance

33
Q

A fixed resistor is an example of an ohmic conductor. What is an ohmic conductor?

A

An ohmic conductor is conductor which follows ohm’s law. This states that the potential difference across an ohmic conductor is directly proprotional to the current flowing through it given that the physical conditions remain constant.

34
Q

Examples of non-ohmic conductors?

A

Filament lamp and diodes

35
Q

Describe the current-potential graph of a filament lamp.

A

At low V, I increases proportionally.
As V continues to increase further, the temperature of the filament lamp increases and thus the resistance across it increases. This is because the particles/ions vibrate with a greater amplitude so it is more difficult for electron to flow through it.
Therefore, the rate of increase of I with V decreases.

36
Q

What are thermistors?

A

Thermistors are components whose resistance is dependant on temeprature.

37
Q

Describe how resistance varies with increasing temeprature for an NTC thermistor.

A

For an negative coefficient temperature thermistor, resistance decreases with increasing temperature.

38
Q

Draw a resistance-temperature graph for an NTC thermistor.

A

Look at notes.

39
Q

What is a light dependant resistor (LDR)?

A

LDRs are components whose resistance is dependant on the light intensity incident on it.

40
Q

Describe how resistance varies with increasing light intensity for an LDR?

A

As light intensity increases, resistance decreases.

41
Q

Draw a resistance-temperature graph for an LDR

A

Look at notes.

42
Q

What are ideal diodes?

A

Ideal diodes are components that allow current to flow through it in one direction only.

43
Q

In reality diodes are not perfect why?

A

In reality diodes need a forwards junction potential to allow current to flow through it.
It also has a breakdown voltage in the reverse direction so negative current will flow through it.

44
Q

Current in a series circuit?

A

Current is the same at any point/across any component in a series cicuit.

45
Q

Current in a parallel circuit?

A

Current is shared between the different branches in a parallel based on their resistances. The greater the resistance of a branch, the lower the current that will flow through it.

46
Q

Potential difference in a series circuit?

A

Potential difference is shared between all the components in a series circuit in ratios of their resistance. The greater the resistance of a component, the greater the potential difference across it.

47
Q

Potential difference in a parallel circuit?

A

Potential difference is the same across each branch of a parallel circuit.

48
Q

How is the total resistance in a series circuit calculated?

A

The total resistance in a series circuit is the sum of all the the individual resistances of each compoenent in the series circuit.

49
Q

How is the total resistance in a parallel circuit calculated?

A

The total resistance in a parallel circuit is given by the expression:

1/R = 1/R1 + 1/R2 + 1/R3

This tells us the total resistance of a parallel combination is less than that of any individual resistor.

50
Q

What is power?

A

Power is the rate of energy transfer.

51
Q

Power, Energy transferred, time equation?

A 
Power = Energy transferred/Time
P = E/t
W = J/s
52
Q

Equations to calculate electrical power?

A 
P = IV
P = I²R
P = V²/R
53
Q

How to calcualate energy transferred without using E = Pt?

A 
E = IVt
E = I²Rt
E = V²t/R
54
Q

What are step up transformers and what are they used for?

A

Step up transformers are used to increase the potential difference and decrease the current so that electricity can be transferred from power stations to the national frid without energy loss as heat)

55
Q

What are step down transformers and what are they used for?

A

Step down transformers are used to decrease the potential difference but increase the current for domestic use - safer and reduces the risk of sparks.

56
Q

Structure and function of a transformer.

A

Transformers consist of a primary coil wrapped around a core.
When a current flows through the primary core, it creates a magnetic current which induces a current in the secondary coil.
The current and voltage can be altered by varying the ratio of turns in the primary coil and secondary coil.

57
Q

How efficient are transformers?

A

Transformers are a 100% efficient (unless stated otherwise).

58
Q

What equation do you need to know that relates coils to current in primary and secondary coil?

A

no. of turns in primary coil/ no. of turns in secondary coil = potential difference in primary coil/potential difference in secondary coil.

n1/n2 = v1/v2

59
Q

Primary potential difference, primary current, power equation?

A 
Power = primary potential difference x primary current
W = V x A
60
Q

secondary potential difference, secondary current, power equation?

A 
Power = secondary potential difference x secondary current
W = V x A
61
Q

Examples of conductors?

A

Metal, aqueous ionic solutions, graphite

62
Q

Examples of insulators?

A

Plastic, paper, rubbet, glass, dry air.

BMAT (3 decks)

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