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