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Physics > Electrons Waves And Photons > Flashcards

Electrons Waves And Photons Flashcards

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1
Q

Define electric current

A

The rate of flow of charge

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2
Q

One ampere is the same as…

A

one coulomb of charge passing a given point per second

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3
Q

Define the coulomb

A

The electric charge flowing past a point in one second when there is an electric current of 1A

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4
Q

How does an object become charged?

A

From the loss or gain of electrons

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5
Q

What are the charge carriers in a metal?

A

Electrons

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6
Q

Which way does conventional current flow?

A

From positive to negative (in metals electrons travel from negative to positive which is not conventional)

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7
Q

What is the name given to liquids which conduct electricity?

A

Electrolytes

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8
Q

What are the charge carriers in a liquid?

A

Ions

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9
Q

What is a cathode?

A

Negatively charged electrode

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10
Q

What is an anode?

A

Positively charged electrode

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11
Q

What is a cation?

A

Positively charged ion

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12
Q

What is an anion?

A

Negatively charged ion

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13
Q

How much resistance would an ideal ammeter have?

A

No resistance to reduce effect on current

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14
Q

What is meant by the conservation of charge?

A

Charge cannot be created or destroyed and in any interaction the charge before and after must be the same.

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15
Q

State Kirchhoff’s first law in words

A

For any point in an electrical circuit, the sum of currents into that point must be equal to the sum of the currents out of the same point. This is because charge must be conserved.

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16
Q

State the equation form of Kirchhoff’s law

A

It = I1 + I2 + …

Where the charge is flowing from the total towards the other branches

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17
Q

Define number density

A

The number of free electrons per cubic metre of material. The higher the number density, the better the conductor. Units are m-3

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18
Q

Compare the number density of conductors, insulators and semi-conductors

A

Conductors have a high number density, insulators have 0 and semi-conductors have a number density in between the two

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19
Q

Define mean drift velocity

A

The average velocity of electrons as they move through the wire

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20
Q

List 3 rules for drawing circuit diagrams

A
  1. Only use the OCR circuit symbols
  2. Do not leave any gaps in between the wires
  3. Draw lines as straight as possible
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21
Q

What is the difference between a battery and a cell?

A

A cell is a single chemical energy source with a positive and negative terminal. A battery is more than one cell in series.

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22
Q

Define potential difference

A

A measure of the transfer of energy by charge carriers

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23
Q

One volt is…

A

The pd across a component when 1J of energy is transferred per unit charge passing through the component

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24
Q

What resistance should an ideal voltmeter have?

A

Infinite resistance

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25
Q

Define e.m.f. (electromotive force)

A

Describes when work is done on the charge carriers. This is the charges gaining energy as they pass through a power source

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26
Q

What is the difference between e.m.f. and p.d.?

A

Pd transfers energy away from the charge carriers whereas emf transfers energy to charge carriers by doing work on them

27
Q

What is an electron gun?

A

An electrical device used to produce a narrow beam of electrons which can be used to ionise particles by adding or removing electrons from atoms

28
Q

What is the electron gun used for?

A

They are used in electron microscopes, mass spectrometers and oscilloscopes

29
Q

Define thermionic emission

A

The emission of electrons through the action of heat

30
Q

Define the Ohm

A

The resistance of a component when a p.d. of 1V is produced per ampere of current

31
Q

Define resistance

A

A property of a component calculated by dividing the potential difference across it by the current; the ratio

32
Q

Ohm’s law

A

For a metallic conductor kept at a constant temperature, the current in the wire is directly proportional to the p.d. across its ends

33
Q

What is a diode?

A

A component that only allows current to flow in a single direction

34
Q

What is the function of a thermistor?

A

To detect changes in temperature with a negative temperature coefficient

35
Q

What is the function of the LDR?

A

To detect changes in light

36
Q

What materials are LDRs and thermistors made from?

A

LDR - usually cadmium sulfide
Thermistor - typically semiconductor with negative temperature coefficient

37
Q

3 factors that affect the resistance of a wire

A

> Material of the wire
The length of the wire
The cross-sectional area of the wire

38
Q

Define resistivity

A

The resistivity of a material at a given temperature is the product of the resistance of a component and its cross-sectional area, divided by its length

39
Q

What is electrical power?

A

The rate of the transfer of energy through the circuit

40
Q

Define the kilowatt-hour

A

The energy transferred by a device with a power of 1kW operating for a time of 1 hour

41
Q

What are 3 alternative phrases for power?

A

> Rate of energy transfer
Energy transferred per second
The rate of work done

42
Q

State Kirchhoff’s second law

A

In any circuit, the sum of the electromotive forces is equal to the sum of p.d. around a closed loop. This is because energy must be conserved.

43
Q

How is e.m.f. split between components in series?

A

It is shared between components, if two components have the same resistance it will be split equally between them

44
Q

How is e.m.f. split between components in parallel?

A

In each loop the total p.d. will be equal to the e.m.f.

45
Q

Define internal resistance

A

The resistance of a source of e.m.f. due to its construction which causes a loss of energy/p.d. as the charge passes through the source

46
Q

Define “lost volts”

A

The difference between the e.m.f. and the p.d. across the power source

47
Q

Define terminal p.d.

A

The p.d. measured at the terminals of a power source

48
Q

Under what condition is e.m.f. equal to terminal p.d.?

A

When the current is very small

49
Q

What is the function of a potential divider circuit?

A

To vary the p.d. when connected to a fixed input for specific use cases

50
Q

What is a progressive wave?

A

An oscillation that travels through matter and transfer energy from one place to another

51
Q

What is a transverse wave?

A

The oscillations are perpendicular to the direction of energy transfer

52
Q

What is a longitudinal wave?

A

The oscillations are parallel to the direction of energy transfer

53
Q

What are compression and rarefaction in a longitudinal wave

A

Particles bounce of each other as energy is transferred so there are areas of high pressure (compression) and low pressure (rarefaction)

54
Q

Define displacement in a transverse wave

A

Distance from the equilibrium position in a particular direction

55
Q

Define amplitude in a transverse wave

A

Maximum displacement from the equilibrium position

56
Q

Define wavelength in a transverse wave

A

Minimum distance between two points in phase on adjacent waves

57
Q

Define the time period of an oscillation

A

The time taken for one oscillation to move one whole wavelength past a given point

58
Q

Define the frequency of an oscillation

A

The number of wavelengths passing a given point per unit time

59
Q

What is a wave profile?

A

A graph showing the displacement of the particles in the wave against the distance along the wave

60
Q

Define phase difference

A

The distance between the displacement of particles along a wave measured in degrees or radians

61
Q

What does it mean if two particles are in phase?

A

They are oscillating perfectly in step with each other

62
Q

What does it mean if two particles are in antiphase?

A

They are oscillating completely out of step with each other (π radians phase difference)

63
Q

What equipment is used to determine the frequency of a wave?

A

An oscilloscope which shows p.d. against time for any signal fed in

Physics (6 decks)

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