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physics paper 2 > electric > Flashcards

electric Flashcards

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1
Q

current

A

rate of flow of charge

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2
Q

e

A

elementary charge

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3
Q

examples of charge carriers

A

electrons - in metals
ions in electrolytes

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4
Q

conventional current

A

flow of positive charge, flows from positive to negative

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5
Q

electron flow

A

current flows from negative to positive

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5
Q

kirchoffs fist law

A

sum of current entering a junction is the same as the sum of the current leaving a junction

charge is conserved

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6
Q

mean drift velocity

A

average velocity of the charge carriers due to the applied electric field, it has to be an average because they are often moving randomly in all directions

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7
Q

put conductors, semi conductors and insulators in order from highest n to lowest

A

highest = conductors
semiconductors
lowest = insulators

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8
Q

potential difference

A

work done per unit charge, the difference in potential between to points in a circuit

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9
Q

what is the difference between voltage and emf

A

voltage is the energy transferred per coulomb across a load resistance

emf is the total amount of work done by the battery per coulomb

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10
Q

true or false: the kinetic energy of an electron is multiplied by its charge multiplied by the voltage

A

true, eV = 1/2 mv^2

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11
Q

resistance

A

the potential difference required for each unit of current that flows through a resistor / how difficult it is for current to flow through an appliance

R = V/I

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12
Q

1 ohm

A

when a resistor is subject to a voltage of 1V and allows a current of 1A through, its resistance is 1 ohm

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13
Q

ohmic conductor

A

conductor that obeys ohms law

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14
Q

ohms law

A

the current through an ohmic conductor is directly proportional to the potential difference across it, this is only true if the temperature is constant

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15
Q

gradient of potential diff graph

A

1/R as gradient = rise in current/charge in potential difference

16
Q

what does an s shaped graph represent

A

a filament lamp
as current increases resistance increases

17
Q

why does the current increasing on a filament lamp cause an increase in resistance

A
  • flow of current causes collisions between electrons and the metal lattice
  • these collisions increase the temp of lattice
  • as temp increases more collisions occur causing the resistance to increase
18
Q

diode

A

appliance that only allows current to flow in one direction

graph is flat then curves upwards

19
Q

LDR

A

a semiconductor that is sensitive to light: as the light intensity increases the resistance decreases

20
Q

how does a thermistor work

A

similar to LDR but as the temp increases the resistance decreases, negative temp coefficient

21
Q

resistivity

A

property of a metal which shows how easy or difficult it is is for current to flow in the metal

P= RA/L

22
Q

experiment to determine resistivity

A
  • measure diameter of wire
  • use diameter to calc CSA
  • set up circuit
  • vary length and record voltage and current
  • use R = V/I to work out resistance
  • plot graph of resistance against length
  • grad = resistivity / area
23
Q

true/false: the resistivity of both metals and semiconductors increases with temp

A

false:

  • the resistivity of a metal increases with temp because as the metal ions heat up they vibrate more and the electrons bang into them and slow down
  • some semi conductors get less resistive as temp increases, because supplying energy actually causes more charge carriers to be released so current can flow more easily
24
Q

power

A

rate of energy transfer

25
Q

why do electricity companies use KWH rather than joules or watts

A

impractical

26
Q

kirchoffs second law

A

for any path of a circuit the sum of all the pd must equal the total emf of the circuit

27
Q

true/false: adding a resistor to a circuit in parallel will always reduce the total resistance

A

true

tot resistance drops the more paths there are for current to take

28
Q

true/false: in parallel circuits the total voltage in each loop is the same

A

true

Vtot = V1=V2…

29
Q

how does the current vary between each component of a series circuit

A

the current through all of the components is the same so the current does not vary

30
Q

if you connect two cells in series with positive to positive what will the total emf be

A

e1+e2

31
Q

true/false: the emf of a source and its terminal voltage will always be the same

A

false

not all the energy given to the charges in the source makes it out of the cell

32
Q

internal resistance

A

resistance with in a power source due to the materials and components which make it up

33
Q

lost volts

A

difference in voltage between that supplied by the source and the amount available to the circuit

34
Q

experiment to determine the internal resistance of a source

A

set up circuit with a source, ammeter and variable resistor in series and a voltmeter in parallel

vary the resistance and measure the voltage and current

plot graph off V/I

V = -rL + e

internal resiatbce = -m

35
Q

purpose of potential divider

A

provide variable potential difference or to provide a constant specific potential difference

36
Q

how does voltage across component in a potential divider correspond to its resistance

A

proportion of the total voltage which is dropped across the component is equal to the proportion of the circuit resistance which its contributes

V/Vt = R/Rt

37
Q

how can a potential divider circuit be used as a sensing circuit

A
  • put resistor that varies with the desired condition in the potential divider
  • insert the responding load over either the variable or fixed resistor depending on how the circuit should work

physics paper 2 (8 decks)

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