section 4: electricity

Question 1

what is current made because of

Answer 1

the flow of charged particles / charge carriers

Question 2

charge carriers in metals

Answer 2

e-

Question 3

charge carriers in salt solution

Answer 3

ions

Question 4

what happens to e- in an insulator

Answer 4

each e- is attached to an an atom which it cannot move away from.

Question 5

what happens when voltage is applied across an insulator

Answer 5

no current passes through as e- cant move through

Question 6

what happens to e- in a metallic conductor

Answer 6

most e- are attached to atoms but some are delocalised.

Question 7

what happens when voltage is applied across an metallic conductor

Answer 7

delocalised e- are attracted towards the positive terminal of the metal

Question 8

what happens to e- in a semiconductor

Answer 8

charge carriers increase with temp

Question 9

what happens to resistance of a semiconductor when temp is rasied

Answer 9

increase

Question 10

how do e- deliver energy in a simple circuit

Answer 10

e- takes energy from battery as it passes through
deliver energy to bulb (or anything)
re enter battery via positive terminal

Question 11

define potential difference

Answer 11

work done per unit charge

Question 12

define emf

Answer 12

electrical energy produced per unit charge passing through the source

Question 13

what 2 effects are created when a current passes through a component with resistance

Answer 13

heating
magnetic

Question 14

whats work done transferred to in a device with resistance and why

Answer 14

thermal energy - charge carriers collide with atoms in the device and transfer energy to them, so atoms vibrate and resistor becomes hotter

Question 15

whats work done transferred to in an electric motor

Answer 15

kinetic energy

Question 16

whats work done transferred to in a loudspeaker

Answer 16

sound energy

Question 17

why does a voltmeter have to be in parallel

Answer 17

so it and the component have the same pd

Question 18

what does a current/voltage graph look like

Answer 18

straight line through the origin

Question 19

define ohms law

Answer 19

the pd across a metal conductor is proportional to the current through it, provided the physical conditions dont change.

Question 20

unit for resistivity

Answer 20

ohm metre (Ωm)

Question 21

how to determine the resistivity of a wire

Answer 21

Calculate cross sectional area.
measure resistance at different lengths of wire and plot on a graph of R against L.
the resistivity is the gradient X cross sectional area

Question 22

define superconductor

Answer 22

a device made of material with 0 resistivity at and below a critical temp

Question 23

when does a superconductor lose its superconductivity

Answer 23

when temp is raised above the critical temp

Question 24

what are superconductors used for

Answer 24

high power electromagnets

Question 25

what does a diode do

Answer 25

only allow current in 1 direction

Question 26

what does a graph of current against voltage look like for a: wire. lamp. thermistor. diode.

Answer 26

wire - straight line through origin, y = x lamp - curved, increases up to origin fast, slower after origin. thermistor - straight line through origin. steeper gradient means higher temp. diode - very low gradient through the origin, hits 0.6V and gradient increases lots

Question 27

why does resistance increase with temp

Answer 27

positive ions vibrate more so harder for charge carriers to pass through the metal as easily

Question 28

1 rules for direct current in series

Answer 28

The current passing through each components is the same.

Question 29

2 pd rules for direct current

Answer 29

Add each components pd to get total pdin series the pd across components in parallel is the same.

Question 30

whats internal resistance due to

Answer 30

opposition to the flow of charge through a source

Question 31

as current increases, what happens to terminal pd

Answer 31

decreases

Question 32

when is maximum power delivered

Answer 32

when the load resistance is equal to the internal resistance

Question 33

when is terminal pd equal to cell emf

Answer 33

at 0 current

Question 34

on a graph of terminal pd vs current, whats the y intercept and gradient

Answer 34

y intercept = emf gradient = internal resistance

Question 35

equation for current through a cell

Answer 35

current = cell emf/ total circuit resistance

Question 36

rules for circuits with cells in series

Answer 36

if cells connected in same direction, add emfs for the net emf. If cells connected in opposite directions, the net emf is the difference between the emfs of the cells. total internal resistance is the sum of individual internal resistance.

Question 37

what makes up the potential divider

Answer 37

2 or more resistors in series with each other with a source of fixed pd

Question 38

is the pd divided between components in the potential divider

Answer 38

yes

Question 39

3 things a potential divider can be used for

Answer 39

supply a pd which is fixed. supply a variable pd. supply a pd that varies with a physical condition such as temp or pressure.

Question 40

how to supply a fixed pd through a potential divider

Answer 40

pd is split between the resistors.

Question 41

.

Answer 41

..

Question 42

2 things a variable potential divider can be used for

Answer 42

audio volume control in a loudspeaker. vary brightness in a bulb.

Question 43

how does a sensor circuit work

Answer 43

produces an output pd which changes depending on a physical variable such as temp or light intensity

Question 44

2 sensory circuits and what makes them up

Answer 44

temperature sensor - potential divider and variable resistor. light sensor - LDR and variable resistor