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A level Physics > Unit 2.1 - Conduction of electricity > Flashcards

Unit 2.1 - Conduction of electricity Flashcards

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1
Q

What are electrical currents caused by?

A

The movement of charged particles (electrons)

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2
Q

What does the movement of electrons cause?

A

Electrical currents

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3
Q

What type of charges is it that always moves in currents?

A

Negative

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4
Q

Unit of charge

A

Coulomb (C)

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5
Q

Coulomb unit

A

Unit of charge

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6
Q

Symbol for charge

A

q or Q (mostly capital Q for WJEC)

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7
Q

What’s Q the symbol for?

A

Charge

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8
Q

Charge of 1 electron

A

-1.6x10^-19C
(In data book)

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9
Q

How many electrons in 1 coulomb?

A

1
—
1.6x10^-19

= 6.25x10^18 electrons

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10
Q

How many protons in one coulomb and why?

A

6.25x10^18 (the same as electrons) as they’re the same size as electrons, just positively charged

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11
Q

How is an object that’s lost electrons charged?

A

Positively

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12
Q

How is an object that’s gained electrons charged?

A

Negatively

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13
Q

Current

A

The rate of flow of charge

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14
Q

The rate of flow of charge

A

Current

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15
Q

Conductors

A

Materials where he charges are in constant motion inside them

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16
Q

Give an example of a material that are all conductors

A

Metals

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17
Q

How can metals conduct electricity?

A

-have ions arranged in a crystalline lattice
-regular “corridors” along the structure in all directions
-outer electrons are freer than inner electrons
-move from atom to atom throughout the lattice
-“Corridors” - free to drift throughout the lattice

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18
Q

What type of process is metals conducting electricity and why?

A

Continuous process
Due to the thermal energy of the metal

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19
Q

Why is a metal conducting a current continuous?

A

Due to the thermal energy of the metal

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20
Q

Why does a piece of metal feel cold when you touch it?

A

Your hand is providing kinetic energy to the free electrons where the metal is being touched - electrons move away, taking thermal energy from the hand (thermal conduction)

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21
Q

Thermal conduction when touching a metal

A

A hand provides kinetic energy to the free electrons in a metal when touched, causing the electrons to move away, taking the thermal energy from the hand

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22
Q

2 examples of electrical fields

A

Potential difference and voltage

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23
Q

How is an electrical field set up?

A

Across the 2 ends of a metal

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24
Q

What happens when electrons are in an electrical field?

A

Random motion of free electrons pushed to 1 direction, towards the positive end

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25
Q

When electrons move towards the positive end when in an electrical field, how do they travel?

A

Don’t zip in a straight line, just have a general drift in one direction

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26
Q

Electrical current

A

When electrons drift towards 1 direction when in an electrical field

27
Q

When electrons drift towards 1 direction when in an electrical field

A

Electrical current

28
Q

Unit of electrical current

A

Amperes (A)

29
Q

What is the Ampere the unit of?

A

Electrical current

30
Q

Ampere definition

A

A current of 1 ampere flows if 1 coulomb of charge passes in 1 second

31
Q

Equation for calculating electrical current

A

I = ∆Q
——
∆t

32
Q

What does the symbol I (capital i) stand for?

A

Current (A)

33
Q

Current symbol

A

I (capital i)

34
Q

Equation for calculating a current in words

A

Current (A) = rate of charge (c)
————————
Time (s)

35
Q

Which of the following is a base unit - ampere or coulomb?

A

Ampere

36
Q

Derivation of coulomb unit

A

As

37
Q

What is current measured as? What is this known as?

A

Flow from + to -
Conventional current

38
Q

Conventional current

A

Flow from + to -

39
Q

What’s the difference between conventional current and electrical current?

A

Electrical current involves the movement of negative electrons, so they move from a - to a + direction
(In the opposite direction)

40
Q

How can we calculate charge on a current-time graph?

A

Area underneath

41
Q

The area underneath of which type of graph can give us important data for this unit?

A

Are underneath a current-time graph = charge

42
Q

How can we calculate charge on a graph and what type of graph would this be?

A

Area underneath a current-charge graph

43
Q

What do electrons do in a wire when a potential difference is applied?

A

Move a distance l along the wire in a certain time

44
Q

What can l be replaced with for the purpose of the I=nAve equation and how come?

A

vt, due to the equation for velocity, where l is the displacement

45
Q

What equation can be used to calculate the drift velocity of electrons?

A

I = nAve

46
Q

What are the steps in deriving the equation for current in terms of drift velocity of electrons (I = nAve)?

A
  1. Volume of cylindrical wire
    A x vt (remember, using the velocity equation, the displacement l is not vt)
  2. Number of free electrons in the wire
    n x Avt
    where n = the number of free electrons per m^3
  3. Total charge (Q)
    Q = nAvt x e
    where e = the charge of 1 electron (1.6x10^19)
  4. Current (I)
    I = ∆Q. =. nAvte. = nAve
    ——. ———
    ∆t. t
47
Q

What is different for al metals in the I = nAve equation?

A

The value of n (the number of free electrons per m^3)

48
Q

How do we calculate n, the number of free electrons per m^3?

A

Number of free electrons
————————————. (m^-3)
Volume of conductor

49
Q

Compare how free electrons move before and after a potential difference is applied

A

Before
Randomly
No overall velocity
Free electrons move very quickly

After
Free electrons accelerated = overall velocity
Drift velocity is small

50
Q

If we have twice as many free electrons in one wire compared to another (the same volume), how does the current, drift velocity and amount of free electrons per m^3 differ?

A

Same current
Half the drift velocity
Double the amount of free electrons per m^3

51
Q

If one wire compared to another of the same length has twice the diameter of the other, how does its current, drift velocity and umber of free electrons per m^3 differ?

A

Same current
4x lower drift velocity
Same number of free electrons per m^3

52
Q

Drift velocity definition

A

Resultant of the velocity vectors of the electrons

53
Q

What does “number density” stand for?

A

“n” in I=nAve

54
Q

What type of wire is more likely to overheat and why?

A

Thin, as there’s more collisions in the wire transferring more K.E. into the vibrational energy of the metal (heat energy)

55
Q

What do we do if using a prefix and the original value is squared?

A

Multiply them together to get the new prefix
E.g 1.2mm^2 is not 1.2x10^-3 but 1.2x10^-6

56
Q

What type of graph can we calculate resistance on and how?

A

Current vs potential difference
gradient

57
Q

What are the free electrons in a conductor often referred to as?

A

“electron gas”

58
Q

Is the velocity of each individual electron dependant on the temperature?

A

no, it’s independent on it

59
Q

Draw a triangle relating charge, electrons and electron charge

A

Charge
e I electrons

60
Q

What’s roughly the speed of electrons before a potential difference is applied?

A

1x10^6 ms-1

61
Q

current

A

the rate of flow of charge

62
Q

the rate of flow of charge

A

current

62
Q

the rate of flow of charge

A

current

A level Physics (29 decks)

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