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A-Level Physics > 6 Electricity > Flashcards

6 Electricity Flashcards

1
Q

What does the longer line of a cell/battery represent?

A

the positive terminal

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2
Q

What does the shorter, wider line of a cell/battery represent?

A

the negative terminal

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3
Q

In a circuit, which way does conventional current flow?

A

from positive to negative

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4
Q

Which direction will electrons flow?

A

from negative to positive

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5
Q

Define current

A

the rate of flow of charged particles around a circuit

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6
Q

What are the units of current?

A

Amps

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7
Q

Should ammeters be connected is series or parallel?

A

series

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8
Q

Define potential difference

A

the amount of work done (energy transferred) per unit charge

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9
Q

State the unit of potential difference/voltage

A

Volts

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10
Q

Should voltmeters be connected in series or parallel?

A

parallel

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11
Q

How many electrons are there in one Coulomb?

A

6 x 10^18 electrons

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12
Q

What three methods could be used to help find the voltage split in series?

A
  • use Ohm’s law
  • use ratios
  • use the potential divider equation
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13
Q

State Kirchloff’s second law

A

in a closed series circuit, the sum of the voltages of each component must equal the voltage across the power supply

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14
Q

Define resistance

A

voltage
———-
current

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15
Q

What can the voltage of a power supply also be known as?

A

the electromotive force (EMF)

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16
Q

What does a voltmeter measure?

A

the difference in the potential (energy) carried by each coulomb before and after a component

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17
Q

What is Kirchloff’s first law?

A

the total current entering a junction must equal the total current leaving the junction

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18
Q

What is Ohm’s law?

A

the current through a conductor is directly proportional to the potential difference across it, provided the physical conditions do not change

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19
Q

What is a component that obeys Ohm’s law known as?

A

an ohmic conductor

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20
Q

For an ohmic conductor, what will an I against V graph look like?

A

a straight line through the origin

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21
Q

For an ohmic conductor, what happens to resistance when potential difference is doubled?

A

nothing, resistance remains constant

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22
Q

What are components that do not follow Ohm’s law called?

A

non-ohmic conductors

23
Q

State four examples of non-ohmic conductors

A
  • filament bulb
  • thermistor
  • light dependent resistor (LDR)
  • diode
24
Q

For a metal, what happens when it heats up? Why?

A
  • resistance increases

- the vibrations of the ion lattice will increase, meaning electrons will collide more frequently with the ion lattice

25
Q

Why don’t insulators allow current to flow easily?

A

there a very few charge carriers (electrons) available

26
Q

State three examples of semi-conductors

A
  • thermistor
  • light dependent resistor (LDR)
  • diode
27
Q

For a semi-conductor, what happens when it heats up? Why?

A
  • resistance decreases

- more charge carriers become available

28
Q

How does the resistance of a diode change with voltage?

A
  • forward bias: initially high resistance (gives small current), at 0.6-0.7 V, resistance decreases rapidly (current increases)
  • reverse bias: high resistance (almost zero current)
29
Q

What four factors affect the resistance of a wire?

A
  • temperature
  • length
  • cross-sectional area
  • the material
30
Q

What is the effect of increasing temperature on the resistance?

A
  • the higher the temperature, the more the lattice vibrates, increasing the chance of electrons colliding
  • therefore resistance increases
31
Q

What is the effect of increasing the length of wire on the resistance?

A
  • the longer the wire, the greater the number of atoms, therefore the greater the chance of collision
  • therefore resistance increases
32
Q

What effect does increasing the diameter of the wire have on the resistance?

A
  • increasing the width of the diameter increases the amount of charge that can pass through
  • therefore resistance decreases
33
Q

What is resistivity?

A

a measure of how easily current can flow through a material

34
Q

Is resistivity a property of the material or the sample?

A

resistivity is a property of the material

35
Q

What is the equation used to calculate resistivity?

A

resistivity = resistance x cross-sectional area
———————————————-
length

36
Q

What is a superconductor?

A

a material with zero resistance when it is at or below the critical temperature

37
Q

State three uses for superconductors and their advantages

A
  • power cables: transmit electricity without loosing any power
  • electromagnets: high magnetic field strengths
  • computers: high speeds
38
Q

Define power

A

the rate of transfer of energy

39
Q

What is power measured in?

A

Watts

40
Q

Give an equation which connects work done, potential difference, current and time

A

W = VIt

41
Q

What causes internal resistance inside a battery?

A

collisions between electrons and atoms inside the battery

42
Q

What is the definition of e.m.f?

A

the energy transferred by a voltage source per unit charge

43
Q

Define internal resistance

A

the internal resistance of a source is the loss of potential difference per unit current in the source when a current passes through the source

44
Q

How can internal resistance be found from a graph of terminal-voltage against current?

A

negative of the gradient

45
Q

How can e.m.f be found from a graph of terminal-voltage against current?

A

y-intercept

46
Q

What happens to the EMF when identical cells are arranged in series?

A

their individual EMFs will add together

47
Q

What happens to the EMF when identical cells are arranged in parallel?

A

their individual EMFs won’t add together

48
Q

What are the disadvantages of arranging identical cells in series?

A
  • their internal resistances will add together, reducing the size of the current
  • if one cell breaks, the whole circuit stops working
49
Q

What are the advantages if arranging identical cells in parallel?

A
  • resistance is reduced allowing for larger current

- if one cell breaks the circuit continues to work

50
Q

What is a potential divider?

A

a combination of resistors in series connected across a voltage source

51
Q

What is the EMF supplied known as when dealing with potential dividers?

A

voltage in

52
Q

Compare the ability for a variable resistor and a potentiometer to vary current

A
  • variable resistor: can vary current but not as sensitively and cannot achieve 0A
  • potentiometer: can vary current sensitively from 0A to a maximum
53
Q

Compare the ability for a variable resistor and a potentiometer to vary potential difference

A
  • variable resistor: can vary p.d. but not as sensitively and cannot achieve 0V
  • potentiometer: can vary p.d. sensitively from 0V up to EMF
54
Q

Which is easier to connect: a variable resistor or a potentiometer?

A

variable resistor

A-Level Physics (15 decks)

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