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Physics > Current Electricity > Flashcards

Current Electricity Flashcards

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1
Q

what is current

A

the rate of flow of charge

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2
Q

what is potential difference/voltage

A

the energy transferred per unit charge between two points in a circuit

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3
Q

what is resistance

A

a measure of how difficult it is for charge to pass trough a component

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4
Q

what does ohm’s law state

A

that for an ohmic conductor current is directly proportional to the potential difference across it given that physical conditions are kept constant

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5
Q

what is an example of an ohmic conductor

A

a resistor

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6
Q

why does a diodes graph look like that

A

because it allows current to flow through easily one way but nit the other way so the potential difference and current is very low to begin with as the current cannot flow through easily due to the resistance

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7
Q

why does a filament lamp graph look like that

A

because it contains a metal wire which heats up so at the beginning as it is not very hit current can easily flow through as there is a low resistance how the hotter it gets the higher the resistance so it is more difficult for the current to flow through causing the gradient to decreased

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8
Q

what can we assume about ammeters and voltmeters resistance

A

ammeters have zero resistance and voltmeters have have infinite resistance so no current can flow through it so their measurement of potential difference across a component is exact

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9
Q

what is resistivity

A

is a measure of how easily a material conducts electricity

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10
Q

what does resistivity measure

A

is a measure of how easily a material conducts electricity

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11
Q

what will resistivity give the value of

A

the value of resistance through a material of length 1m and cross sectional area 1m^2

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12
Q

why is resistivity useful

A

because you can compare materials even though they might nit be the same size

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13
Q

what is resistivity also dependent on

A

environmental factors such as temperature

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14
Q

what will happen the resistance if the temp of a metal conductor increases

A

resistance also increases

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15
Q

why does the resistance increase if the temp of a metal conductor increases

A

because the atoms of the metal gain more kinetic energy and move more which causes the electron (charge carriers) to collide with the atoms more frequently causing them to slow down therefore current decreases and resistance increases

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16
Q

in a thermistor what happens to the resistance as the temp increases

A

the resistance decreases

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17
Q

why in a thermistor does resistance decrease when the temp increases

A

increasing the temp causes electrons to be emitted from atoms therefore the number of charge carriers increases and so current increases causing resistance to decrease

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18
Q

what is one application of a thermistor in a circuit

A

is a temperature sensor which can trigger an event to occur once the temp drops or reaches a certain value

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19
Q

what is a superconductor

A

is a material which below a certain temp known as the critical temp has zero resistivity

20
Q

what does the critical temp of a superconductor depend on

A

the material it is made out of

21
Q

which temp do most well known superconductors have a critical temp at

A

0K (-273 Degrees Celsius)

22
Q

what are the applications of super conductors

A
  • power cables which would reduce energy loss through heating to 0 during transmission
  • strong magnetic fields which would not require a constant power source (could be used in maglev trains where there would be no friction between the train and the rail and in certain medical applications
23
Q

how do you add resistances in a series circuit

A

Rt = R1 +R2 +R3 +….

24
Q

how do you add resistances in a parallel circuit

A

1/Rt = 1/R1 + 1/R2 + 1/R3 + ….

25
Q

what is power

A

is the energy transferred over time (rate if energy transfer)

26
Q

what happens to the current and p.d in a series circuit

A
  • the current is the same throughout the circuit
  • the battery p.d is shared across all elements in he circuit, therefore the total um of the voltages across all the elements is equal to the supply p.d
27
Q

what happens to the current and p.d in a parallel circuit

A
  • the sum of the currents in each parallel set of branches is equal to the total current
  • the p.d across each branch is the same
28
Q

in a series circuit what is the total voltage across the cells equal to

A

the sum of the individual voltages of the cells

29
Q

in a parallel circuit what is the total voltage equal to if the cells are identical and why

A

the total voltage is equal to the voltage of one cell this is because the current is split equally between the branches, therefore the overall potential difference is the same as if the total current was flowing through a single cells

30
Q

in DC circuits what is always conserved and what are the name of the laws which describe how this is achieved

A

charge and energy are always conserved and the laws are called kirchoffs laws

31
Q

what is Kirchoff’s 1st law and what does it show

A

the total current flowing into a junction is equal to the current flowing out of the junction
it shows that no charge is lost at any point in the circuit

32
Q

what is Kirchoff’s 2nd law and what does it show

A

the sum of all the voltages in a series circuit is equal to the battery voltage
this shows that no energy is lost at any point in a circuit

33
Q

what is a potential divider

A

is a circuit with several resistors in series connected across a voltage source, used to reduce a required fraction of the source potential difference, which remains constant

34
Q

how can you make a potential divider supply a variable potential divider supply

A

use a variable resistor as one of the resistors in series, therefore by varying the resistance across it, you can vary the potential difference output

35
Q

what could you replace a variable resistor with to form a temp or light sensor

A

a thermistor or LDR

36
Q

when a LDR resistance decreases what happens to the light intensity

A

it increases

37
Q

what has an internal resistance

A

batteries

38
Q

what causes internal resistance

A

caused by electrons colliding with atoms inside the battery, therefore some enrgy is lost before electrons even leave the battery

39
Q

what is the electromotive force

A

is the energy transferred by a cell per coulomb of charge that passes through it

40
Q

what is emf the product of

A

the total resistance and the current of the circuit

41
Q

what is the p.d across a resistor called

A

terminal p.d

42
Q

what is the p.d across a the resistor for internal resistance called and why

A

the lost volts because this value is equal to the energy wasted by the cell per coulomb of charge

43
Q

what is emf the sum of

A

the terminal p.d and the lost p.d

44
Q

how can the emf of a battery be measured

A

by measuring the voltage across a cell using a voltmeter when there is no current running through the cell, which means its an open circuit

45
Q
A

Physics (18 decks)

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