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A Level Physics > Module 4: Chapter 8 - Charge and Current > Flashcards

Module 4: Chapter 8 - Charge and Current Flashcards

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1
Q

What is Electric Charge?

A

Electric Charge is a physical property that all bodies possess, charge can be positive (+) or negative (-)

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2
Q

What are the 2 different types of charge?

A

Positive (+) and Negative (-)

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3
Q

How do charges interact?

A

Charges interact via electrostatic forces causing two of the same charge to repel each other but causing 2 opposite charges to attract each other

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4
Q

What is the unit of electric charge?

A

Coulomb (C)

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5
Q

What is 1 Couloumb of charge?

A

The amount of charge that passes a point per second when there is a current of one amp (1A)

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6
Q

What is the charge of a proton in coulombs?

A

1.6 x 10⁻¹⁹ C

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7
Q

What is the charge of an electron in coulombs?

A

-1.6 x 10⁻¹⁹ C

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8
Q

What is the charge of a copper 2+ ion in coulombs?

A

3.2 x 10⁻¹⁹ C

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9
Q

What is the charge of a Cl- ion in coulombs?

A

-1.6 x 10⁻¹⁹ C

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10
Q

What is the charge of a Uranium Nucleus in coulombs? (atomic number = 92)

A

1.472 x 10⁻¹⁷ C

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11
Q

What is the charge of a Carbon atom in coulombs?

A

0 C

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12
Q

What is the charge of an Iron Nucleus in coulombs? (Atomic Number = 26)

A

4.16 x 10⁻¹⁸

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13
Q

What is the sign for the Elementary charge?

A

e

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14
Q

What is the elementary charge in coulombs?

A

1 e = 1.6 x 10⁻¹⁹ C

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15
Q

What does “Charge is quantised mean”?

A

The charge of any object is an integer multiple of the elementary charge “e”

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16
Q

Convert 1 Coulomb to a multiple of the elementary charge.

A

6.25x10¹⁸ e

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17
Q

What is the elementary charge?

A

The charge of 1 proton or electron

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18
Q

Convert 5.7x10⁻¹⁰ C to a multiple of the elementary charge.

A

3.5625x10⁹ e

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19
Q

Convert 500e to Coulombs.

A

8x10⁻¹⁷ C

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20
Q

What is an electric current?

A

The rate of flow of electric charge

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21
Q

What is the unit for current?

A

Amperes (Amps)

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22
Q

What is the equation for electric current?

A 
I = ΔQ/Δt
(Current = Charge/time)
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23
Q

How does an object become charged?

A

It has gained or lost electrons

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24
Q

How can the net charge of an object be expressed?

A

It can be expressed as a multiple of e:

Q = ±ne

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25
Q

What does “Q = ±ne” represent?

A

The net charge of an object where
Q = charge
n = number of electrons
e = elementary charge

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26
Q

What is the charge in coulombs for the charge -5e?

A

-8x10⁻¹⁹ C

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27
Q

What is the charge in coulombs for the charge +41e?

A

6.56x10⁻¹⁸ C

28
Q

How many electrons must be deposited on an object for it to have a net charge of -15C?

A

9.375x10¹⁹

29
Q

What is the current if 5x10¹⁴ electrons pass through a wire in 1 second?

A

8x10⁻⁵ A

30
Q

What is an uncharged object called?

A

Neutral

31
Q

How does an electric current flow through a metal if one end of the metal is positively charged and the other negative?

A

The structure of a metal is a giant lattice of fixed metal cations surrounded by a sea of negative delocalised (free) electrons. The free delocalised electrons will be attracted to the positive end of the wire and repelled from the negative end of the wire (as like charged repel and opposite charged attract). This will cause a flow of charge (electrons), therefore an electric current will be produced as an electric current is the rate of flow of charge.

32
Q

What is conventional current?

A

Conventional current behaves as if positive charge carriers cause current flow. Conventional current flows from the positive terminal to the negative terminal

33
Q

What is the electron current?

A

The flow of electrons

34
Q

Why is there both a conventional current and electron current?

A

Conventional current was discovered a long time before the discovery of the electron as the charge carrier. As conventional current was so well established (and did not affect calculations), it remains in use.

35
Q

What type of current does “current” refer to?

A

Conventional current

36
Q

What is the difference between conventional current and electron current in a metal wire?

A

Electron flow is the direction that electrons flow through the circuit (from the negative terminal to the positive terminal), whereas conventional current is the direction that a positive charge carrier would flow through the circuit (from the positive terminal to the negative terminal). The electron current and conventional current are in the opposite direction to each other

37
Q

What is an electrolyte?

A

Ionic liquid or ionic solution which can conduct as they contain ions

38
Q

Explain how a current can flow through electrodes and an electrolyte.

A

When the power supply is switched on, the cathode will become negatively charged and the anode will become positively charged. This will cause the positive cations in the electrolyte to be attracted to the cathode, and the negative anions in the electrolyte to be attracted to the anode (as opposite charges attract). At the anode, the anions lose electrons (and form neutral atoms) which flow through the circuit towards the cathode where the cations gain these electrons (and form neutral atoms). This movement of electrons through the circuit and movement of ions in the electrolyte is a flow of charge - and electric current.

39
Q

What is current the movement of in metals?

A

Electrons

40
Q

What is current the movement of in an electrolyte?

A

Ions

41
Q

What is a charge carrier?

A

Any particle which has an electric charge (such as a proton, electron, or ion)

42
Q

Describe the motion of a metal ion in a metal structure.

A

The metal cations are not free to move, however they vibrate around a fixed point and vibrate faster with increased temperature

43
Q

What may a larger current be due to?

A
  • A greater number of electrons moving past a given point each second (a wire with a greater cross sectional area)
  • The same number of electrons moving faster through the metal
44
Q

Why is pure water an insulator but tap water a conductor?

A

Pure water does not contain any charged particles and therefore does not conduct, however tap water contains dissolved ions. Therefore tap water is an ionic solution (an electrolyte) and can conduct.

45
Q

How do you use an ammeter?

A

An ammeter must be placed directly in series with the circuit at the point you want to measure the current

46
Q

Why should an ammeter have minimal resistance?

A

An ammeter is placed in series with the circuit, therefore they should have minimal resistance to reduce the effect they have on the current. An ammeter with a high resistance would decrease the current it is supposed to be measuring.

47
Q

What would a perfect ammeter be like?

A

It would have 0 resistance and therefore have no effect on the current it measures

48
Q

What is the law of conservation of charge?

A

In a closed system, the total charge in the system is conserved. Therefore the total amount of charge is constant

49
Q

What is kirchoff’s first law?

A

At a junction in any circuit, the total current leaving the junction is equal to the total current entering the junction

Σ Iᵢₙ = Σ Iₒᵤₜ

50
Q

What are the values of the unknown currents?

A

i = 7A
ii = 5A

51
Q

What are the values and direction of the unknown currents?

A

iv = 2A to the left
v = 5A to the left
vi = 7A into the junction

52
Q

A single wire is connected to 2 other wires, A and B. If the current in the single wire is 15A, and 1.9 x 10²¹ electrons pass along wire A in 1 minute, calculate the current in wire B to the nearest ampere

A

10A

53
Q

Form an expression for the current in this diagram

A

I₁ + I₂ = I₃

54
Q

Form an expression for the current in this diagram

A

I₁ + I₂ + I₃ = 0

55
Q

What is number density?

A

The number density is the number of free electrons per unit volume. The higher the number density, the greater the number of free electrons per m³ and so the better the electrical conductor

56
Q

How does number density affect conductivity?

A

The greater the number density the greater the conductivity

57
Q

What is the number density of a conductor?

A

Large number density of conduction electrons (in order of 10²⁸ m⁻³)

58
Q

What is the number density of an insulator?

A

Few or no conduction electrons, number density is almost 0

59
Q

What is the number density of a semiconductor?

A

Number density between that of a conductor and that of an insulator (in order of 10¹⁷ m⁻³)

60
Q

What is mean drift velocity?

A

The average speed the charged particle travels along the conductor

61
Q

What is the equation for electric current in a metal (considering mean drift velocity)?

A

I = Anev
Current = Cross sectional area of wire x number density x fundamental charge x mean drift velocity

62
Q

What is the equation for electric current when not in a metal (considering mean drift velocity)?

A

I = Anqv
Current = Cross sectional area of wire x number density x charge of charge carrier x mean drift velocity

63
Q

How does the cross sectional area affect mean drift velocity?

A

The narrower the wire, the greater the mean drift velocity in order for the current to remain the same

64
Q

What are the units for number density?

A

m⁻³

65
Q

Why is mean drift velocity required?

A

Charged particles do not travel in a straight line through a conductor as they collide with other particles in the material. Therefore an average speed is used

66
Q

Why do semiconductors get much hotter than conductors?

A

Semiconductors have a much lower number density than conductors, therefore in order to carry the same current, the mean drift velocity must be much higher. The faster moving electrons causes the temperature to increase much more than in conductors

A Level Physics (29 decks)

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