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Physics > 5 Electricity > Flashcards

5 Electricity Flashcards

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1
Q

what is current

A

rate of flow of charge

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2
Q

which way do electrons flow

A

negative to positive terminal

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3
Q

which way does current flow

A

positive to negative
(opposite to flow of electrons)

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4
Q

what is p.d

A

potential difference of a circuit is the amount of work done to move the charge around the circuit, per unit charge
the ‘push’ that allows the current to flow around the circuit (supplies the power)

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5
Q

what are the properties of an ohmic conductor

A

resistance is constant
current is directly proportional to voltage
current-voltage graph is a straight line

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6
Q

what does a diode do

A

a diode only allows current to flow in one direction unless there are extreme conditions
(unless voltage is other direction is very large)

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7
Q

what is reverse bias

A

the direction in which current is not allowed to flow

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8
Q

what is required for current to flow in reverse bias

A

a very large voltage

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9
Q

what is breakdown voltage

A

the voltage at which current will flow in reverse bias

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10
Q

what is forward bias

A

the direction that current is allowed to flow

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11
Q

what is threshold voltage

A

the point at which the diode will conduct in the forward direction
(0.6V)

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12
Q

what is resistivity

A

the resistivity of a material is a measure of how much resistance a material provides
it is independent of a materials shape or size

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13
Q

what are thermistors

A

electrical components which change their resistance based on their temperature

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14
Q

what is the relationship between temperature and resistance of a negative temperature coefficient thermistor

A

the higher the temperature, the lower the resistance

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15
Q

what are superconductors

A

material with a resistivity of zero below a critical temperature

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16
Q

how do superconductors work

A

because the resistance of a piece of a superconductor is zero, there are no heat losses for currents through them
most superconductors must be cooled to zero, only a few kelvin above absolute zero - this is very expensive and limits the use of superconductors

17
Q

what are superconductors used in

A

magnets needing high currents (MRI machines)

18
Q

when do superconductors occur

A

when free electrons combine to form cooper pairs at low temperatures
these cooper pairs collide with the other atoms in the material and, if the energy of the collision is low, then the cooper pairs do not split and lose energy
so resistivity is zero

19
Q

what material is used to cool MRI magnets

A

liquid helium

20
Q

what is the resistance in a parallel circuit

A

the total resistance is less than the smallest resistor in the parallel circuit
1/Rtotal = 1/R1 +1/R2 +…

21
Q

what is the resistance of a series circuit

A

the total resistance is the sum of each individual resistor

22
Q

what is kirchhoff’s first law

A

the total current arriving at a junction is equal to the total current leaving a junction
‘current splits up’

23
Q

what is kirchhoff’s second law

A

the sum of voltage drops in a closed loop must be equal to zero
energy is conserved

24
Q

what is current convention

A

the current in a circuit flows from positive to negative

25
Q

what is power

A

the rate of transfer of energy

26
Q

when is work done in a circuit

A

when current flows through a component with resistance

27
Q

what do potential dividers do

A

supply constant or variable potential differences from a power supply

28
Q

how do potential dividers work

A

a potential divider uses the resistance of a resistor to change the potential difference across a component

29
Q

what is emf

A

electromotive force is the total voltage produced by the cell

30
Q

how does internal resistance effect a circuit

A

internal resistance reduces the voltage output of the cell before it reaches the circuit

Physics (19 decks)

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