electric currents

Question 1

insulator

Answer 1

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

Question 2

conductor

Answer 2

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

Question 3

electric current

Answer 3

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

Question 4

speed of electric field in a current

Answer 4

around the speed of light

Question 5

proportionality in a wire

Answer 5

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

Question 6

what effect does current always have

Answer 6

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

Question 7

what happens to electric potential energy when charges separated

Answer 7

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

Question 8

electromotive force (ε)

Answer 8

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

Question 9

Electric potential difference

Answer 9

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

Question 10

Kirchoff’s second rule

Answer 10

emf=sum of p.d.s

Question 11

electron-volt

Answer 11

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

Question 12

voltage

Answer 12

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

Question 13

The power provided by a cell=

Answer 13

the total power emitted by the circuit components

Question 14

power

Answer 14

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

Question 15

work-done on a charge when moving through a voltage

Answer 15

W=qV

Question 16

resistance

Answer 16

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

Question 17

drift velocity

Answer 17

average velocity gained from an electric field

Question 18

3 elements of resistance

Answer 18

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

Question 19

resistivity

Answer 19

constant in a material, but increases with temperature

Question 20

ohm’s law

Answer 20

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

Question 21

ohmic components

Answer 21

components that obey Ohm’s law

Question 22

thermister

Answer 22

temperature variable resistor

Question 23

non-ohmic components

Answer 23

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

Question 24

I-V curve

Answer 24

straight if obeys ohm’s law

curves to point towards v axis as temperature increases with resistance

Question 25

specifications of lamps

Answer 25

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

Question 26

Ammeters

Answer 26

connected in series, zero resistance | measures current

Question 27

Voltmeter

Answer 27

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

Question 28

internal resistance in a cell

Answer 28

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

Question 29

effects of current (terminal voltage and collisions)

Answer 29

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

Question 30

optimum resistance

Answer 30

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

Question 31

series

Answer 31

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

Question 32

parallel

Answer 32

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

Question 33

potential divider circuit

Answer 33

potential difference is divided between the various resistances in the circuit

Question 34

Light Dependant resistors (LDR)

Answer 34

low resistance in well lit conditions | high resistance in dark

Question 35

Negative temperature coefficient thermistors

Answer 35

low resistance in warm conditions | high resistance in cold conditions

Question 36

Strain gauges

Answer 36

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