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A-Level Physics > 6 Electricity > Flashcards

6 Electricity Flashcards

(54 cards)

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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?

Study These Flashcards
A

non-ohmic conductors

23
Q

State four examples of non-ohmic conductors

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

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

Study These Flashcards
A
  • resistance increases

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

25
Why don’t insulators allow current to flow easily?
there a very few charge carriers (electrons) available
26
State three examples of semi-conductors
- thermistor - light dependent resistor (LDR) - diode
27
For a semi-conductor, what happens when it heats up? Why?
- resistance decreases | - more charge carriers become available
28
How does the resistance of a diode change with voltage?
- 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
What four factors affect the resistance of a wire?
- temperature - length - cross-sectional area - the material
30
What is the effect of increasing temperature on the resistance?
- the higher the temperature, the more the lattice vibrates, increasing the chance of electrons colliding - therefore resistance increases
31
What is the effect of increasing the length of wire on the resistance?
- the longer the wire, the greater the number of atoms, therefore the greater the chance of collision - therefore resistance increases
32
What effect does increasing the diameter of the wire have on the resistance?
- increasing the width of the diameter increases the amount of charge that can pass through - therefore resistance decreases
33
What is resistivity?
a measure of how easily current can flow through a material
34
Is resistivity a property of the material or the sample?
resistivity is a property of the material
35
What is the equation used to calculate resistivity?
resistivity = resistance x cross-sectional area ———————————————- length
36
What is a superconductor?
a material with zero resistance when it is at or below the critical temperature
37
State three uses for superconductors and their advantages
- power cables: transmit electricity without loosing any power - electromagnets: high magnetic field strengths - computers: high speeds
38
Define power
the rate of transfer of energy
39
What is power measured in?
Watts
40
Give an equation which connects work done, potential difference, current and time
W = VIt
41
What causes internal resistance inside a battery?
collisions between electrons and atoms inside the battery
42
What is the definition of e.m.f?
the energy transferred by a voltage source per unit charge
43
Define internal resistance
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
How can internal resistance be found from a graph of terminal-voltage against current?
negative of the gradient
45
How can e.m.f be found from a graph of terminal-voltage against current?
y-intercept
46
What happens to the EMF when identical cells are arranged in series?
their individual EMFs will add together
47
What happens to the EMF when identical cells are arranged in parallel?
their individual EMFs won’t add together
48
What are the disadvantages of arranging identical cells in series?
- their internal resistances will add together, reducing the size of the current - if one cell breaks, the whole circuit stops working
49
What are the advantages if arranging identical cells in parallel?
- resistance is reduced allowing for larger current | - if one cell breaks the circuit continues to work
50
What is a potential divider?
a combination of resistors in series connected across a voltage source
51
What is the EMF supplied known as when dealing with potential dividers?
voltage in
52
Compare the ability for a variable resistor and a potentiometer to vary current
- variable resistor: can vary current but not as sensitively and cannot achieve 0A - potentiometer: can vary current sensitively from 0A to a maximum
53
Compare the ability for a variable resistor and a potentiometer to vary potential difference
- 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
Which is easier to connect: a variable resistor or a potentiometer?
variable resistor

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