electric currents Flashcards Preview

Physics > electric currents > Flashcards

Flashcards in electric currents Deck (36):
1

insulator

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

2

conductor

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

3

electric current

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

4

speed of electric field in a current

around the speed of light

5

proportionality in a wire

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

6

what effect does current always have

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

7

what happens to electric potential energy when charges separated

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

8

electromotive force (ε)

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

9

Electric potential difference

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

10

Kirchoff's second rule

emf=sum of p.d.s

11

electron-volt

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

12

voltage

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

13

The power provided by a cell=

the total power emitted by the circuit components

14

power

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

15

work-done on a charge when moving through a voltage

W=qV

16

resistance

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

drift velocity

average velocity gained from an electric field

18

3 elements of resistance

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

resistivity

constant in a material, but increases with temperature

20

ohm's law

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

21

ohmic components

components that obey Ohm's law

22

thermister

temperature variable resistor

23

non-ohmic components

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

24

I-V curve

straight if obeys ohm's law
curves to point towards v axis as temperature increases with resistance

25

specifications of lamps

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

Ammeters

connected in series, zero resistance
measures current

27

Voltmeter

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

28

internal resistance in a cell

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

effects of current (terminal voltage and collisions)

larger current increases collisions in cells
larger effect on terminal voltage at lower current

30

optimum resistance

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

31

series

in a line, one after the other
Rt=R1+R2+R3...

32

parallel

division of current to parallel components
1/Rt=1/R1+1/R2+1/R3

33

potential divider circuit

potential difference is divided between the various resistances in the circuit

34

Light Dependant resistors (LDR)

low resistance in well lit conditions
high resistance in dark

35

Negative temperature coefficient thermistors

low resistance in warm conditions
high resistance in cold conditions

36

Strain gauges

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