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IB Physics > electricity > Flashcards

electricity Flashcards

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1
Q

property of matter that causes electric field

A

charge

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2
Q

charge scalar or vector

A

scalar

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3
Q

value of fundamental charge

A

1.6x10^-19

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4
Q

what is fundamental charge

A

smallest amount of charge that exists in ordinary matter - protons and electrons have this same charge but with opposite sign

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5
Q

electric field

A

region of space where an electric force is experienced

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6
Q

field strength (E)

A

the force experienced by a small + charge placed at a point in the field

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7
Q

potential of a sphere

A

the amount of work done per unit charge to bring a small positive charge from infinity to the surface of the sphere

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8
Q

units of potential

A

JC^-1 (same as volt)

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9
Q

coulomb’s law

A

The force experienced by two point charges is directly proportional to the product of their charge and inversely proportional to the square of their separation

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10
Q

law for the force between masses in a) an electric field and b) a gravitational field

A

a) Coulomb’s law

b) Newton’s law

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11
Q

what makes smth a good conductor

A

allows a large current for a given pd

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12
Q

ohm’s law

A

the current through an ohmic conductor is directly proportional to the pd across it provided that the temperature remains constant

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13
Q

why does temperature affect resistance

A

because an increase in temperature means increased lattice vibrations resulting in more collisions between electrons and the lattice

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14
Q

why does increasing the temperature of a semiconductor lead to lower resistance

A

liberates more electrons

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15
Q

primary cell

A

cell that cannot be recharged

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16
Q

emf of a cell layman’s and IB

A
  • the energy provided by a cell or battery per coulomb of charge passing through
  • the work done taking unit charge from one terminal to the other (low potential to high potential)
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17
Q

how many kg in a tonne

A

1000

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18
Q

electric potential energy for a sphere of charge

A

V =Qk/r^2

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19
Q

how many electrons per second to produce 1 amp of current?

A

6.2x10^18

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20
Q

internal resistance

A

the resistance of the components inside a battery.

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21
Q

terminal potential difference what is it and relationship to emf

A

pd across the terminals of the battery

equal to emf, but if a current flows it will be less than emf

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22
Q

what does emf stand for

A

electromotive force

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23
Q

electrical power

A

the rate at which energy is changed from one form to another

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24
Q

kirchhoff’s first law

A

current into junction = current out of junction

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25
Q

kirchhoff’s second law

A

around any closed circuit, the sum of the emfs = the sum of the pds

26
Q

ohm’s law equation

A

V = IR

27
Q

ideal ammeter vs ideal voltmeter

A

Ideal voltmeter has infinite resistance

Ideal ammeter has zero resistance.

28
Q

field strength unit

A

NC^-1

29
Q

EPE (electric potential energy) equation

A

EPE = Vq

30
Q

conventional current flow vs electron flow

A

conventional current moves from high to low potential (ie +ve to -ve) however electrons flow the other way as attracted to +ve

31
Q

convert joules to electron volt (eV)

A

divide by fundamental charge

32
Q

what is an electronvolt

A

energy gained by an electron accelerated through a pd of 1V

33
Q

emf

A

energy converted from chemical to electrical per unit charge

34
Q

electrical power

A

the rate at which energy is changed from one form to another

35
Q

power delivered in a perfect battery

A

energy converted from chemical to electrical per unit time

36
Q

power dissipated in resistor

A

amount of electrical energy converted to heat per unit time

37
Q

electric kettle

A

transfers the heat produced when current flows through a wire element to the water inside the kettle

38
Q

magnetic flux density (B)

A

quantity used to measure how string magnetic field is

39
Q

definition of ampere

A

one ampere is defined as the current that would cause a force of 2x10^-7N/m between two long parallel conductors separated by 1m in a vacuum

40
Q

what does it mean if a lamp is labelled ‘3 volts, 0.6 watts’

A

This means that if the bulb is
connected to 3V then 0.6W of power
is dissipated

41
Q

electric cell

A

device that uses the energy stored in chemicals to arrange charges in such a way that a p.d. is created which can be used to cause a current to flow in a conductor

42
Q

how is chemical energy = electrical PE

A

chemical energy = energy associated with molecules

molecules = charged bodies arranged in such a way that they don’t fly apart

43
Q

when is the pd across r (internal resistance) equal to the EMF

A

when resistance R of external circuit = 0

44
Q

when is the pd across the terminals of the cell equal to the emf?

A 
When I is zero there will be no pd
across r (internal resistance) , so V = E
45
Q

pd across a resistor

A

amount of electrical energy converted to
heat per unit charge so if energy is
conserved

46
Q

why might resistance be greater if power dissipated in the resistor is greater than recommended maximum

A 
When current passes through the
resistor heat is dissipated causing the
temperature of the resistor to increase.
Increased temperature will increase
theresistance.
47
Q

the equation for k when you have a situation with charges not in a vacuum,

A

k= 1/4πε

48
Q

direction of movement of POSITIVE charge

A

Positive charge will always move from high to low potential

49
Q

resistivity

A

the resistance of 1 m3 of substance.

50
Q

why does the ideal voltmeter have high resistance

A

so it doesn’t draw any current

51
Q

magnetic field lines direction

A

always north to south

52
Q

state, in terms of electrons, the difference between a conductor and an insulator

A

a conductor contains ‘free’ electrons and insulators do

not

53
Q

resistance mark scheme definition

A

the ratio of potential difference across a device/load/resistor to current in the device/load/resistor

54
Q

difference in thermal capacity gas heated at constant pressure vs gas heated at constant volume

A

the thermal capacity for gases at constant volume is less, because all the thermal energy supplied goes to increasing the internal energy, so the increase in temperature in the constant volume case is greater

55
Q

why must there be an electric field inside a conductor

A

Because in order to have a current, electrons must be moving along the wire -> so a force (electric force) must be acting on them

56
Q

what is the force on a free electron inside a conductor

A

electric field strength x elementary charge

57
Q

whats a test charge

A

point charge which has no effect on the field in which it is placed

58
Q

what do electric cells do

A

convert chemical energy into electrical potential energy

59
Q

what is a magnetic field

A

a region of space where a small magnetic dipole experiences a turning force

60
Q

why are magnetic poles called north-seeking and south-seeking

A

because they point in those directions if suspended

61
Q

unit of magnetic flux density (B)

A

tesla(T)

62
Q

charge x voltage

A

energy

IB Physics (10 decks)

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