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Physics > electric currents > Flashcards

electric currents Flashcards

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1
Q

insulator

A

all electrons firmly bound to nuclei, does not cause flow of electrons elsewhere

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2
Q

conductor

A

de localized or free electrons that are not bound to any atom of he metal (redistributes charges)

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3
Q

electric current

A

the force per unit length between parallel current carrying conductors (amps)

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4
Q

speed of electric field in a current

A

around the speed of light

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5
Q

proportionality in a wire

A

the current is proportional to the drift velocity and number of electrons per mm of wire

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6
Q

what effect does current always have

A

heating (because of acceleration and collisions of electrons and electric potential energy is transferred to heat energy)

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7
Q

what happens to electric potential energy when charges separated

A

it increases (hence electrons gain electric potential energy through a cell)

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8
Q

electromotive force (ε)

A

the energy per unit charge converted into other form from a battery or power supply (V(=j/coulomb))

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9
Q

Electric potential difference

A

the change of electric potential energy when 1 C (coulomb) moves between two points

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10
Q

Kirchoff’s second rule

A

emf=sum of p.d.s

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11
Q

electron-volt

A

the energy gained or lost by an electron when it moves through a voltage of 1 volt
eV=0.5mv^2 1eV=1.6*10^-19j

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12
Q

voltage

A

energy available per electron, therefore if more available it will speed up

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13
Q

The power provided by a cell=

A

the total power emitted by the circuit components

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14
Q

power

A 
the power (energy/second) supplied = the amount of electrical energy each coulomb of charge acquires (emf) and the number of coulombs passing through per second (current)
P=emf*current (Amps)
the power dissipated (such as from resistor) = the amount of electrical energy each coulomb transfers (p.d) and the current
P=p.d*current
P=VI
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15
Q

work-done on a charge when moving through a voltage

A

W=qV

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16
Q

resistance

A

the opposition to the flow of current (V/coulomb)

ratio of loss of electric Ep/per unit charge to the quantity of mobile charge per mm by the drift velocity

17
Q

drift velocity

A

average velocity gained from an electric field

18
Q

3 elements of resistance

A

internal structure of the metal, resistivity
resistance proportional to length
inversely proportional to the cross-sectional area of the wire (ie thinner wire is faster with more cars)
resistance=resistivity*length/cross-sectional area
=pl/A

19
Q

resistivity

A

constant in a material, but increases with temperature

20
Q

ohm’s law

A

the resistance of a conductor constant if temp constant or current proportional to pd if temp constant

21
Q

ohmic components

A

components that obey Ohm’s law

22
Q

thermister

A

temperature variable resistor

23
Q

non-ohmic components

A

do not obey ohm’s law because of heating effect (eg filament lamps)

24
Q

I-V curve

A

straight if obeys ohm’s law

curves to point towards v axis as temperature increases with resistance

25
Q

specifications of lamps

A

operating voltage, the current at the voltage and power (input/output) required. under these the lamp is at normal brightness, lower will be dimmer and higher brighter but less long lasting

26
Q

Ammeters

A

connected in series, zero resistance

measures current

27
Q

Voltmeter

A

connected in parallel, infinite resistance to measure the change in voltage from one side of a component to another

28
Q

internal resistance in a cell

A

chemical reactions still provide same energy, but electrons collide in the cell and the chemical energy is transferred to thermal energy as well as electric potential energy
ε=I(R+r) where R is the total resistance of external circuit and r internal resistance of the cell. ε is the emf

29
Q

effects of current (terminal voltage and collisions)

A

larger current increases collisions in cells

larger effect on terminal voltage at lower current

30
Q

optimum resistance

A

when power delivered to the external resistance will be a maximum and this happens to be when the external resistance= internal resistance

31
Q

series

A

in a line, one after the other

Rt=R1+R2+R3…

32
Q

parallel

A

division of current to parallel components

1/Rt=1/R1+1/R2+1/R3

33
Q

potential divider circuit

A

potential difference is divided between the various resistances in the circuit

34
Q

Light Dependant resistors (LDR)

A

low resistance in well lit conditions

high resistance in dark

35
Q

Negative temperature coefficient thermistors

A

low resistance in warm conditions

high resistance in cold conditions

36
Q

Strain gauges

A

as the gauge is stretched, then the resistance increase with smaller diameter wire.

Physics (10 decks)

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