electricity

what are conductors

materials that allow the flow of electrical charge

What must happen to circuits to make them complete

all switches must be closed for the circuit to work

if there is higher resistance what does this mean for energy

more energy is transferred

how to make a lamp dimmer

add resistor

what happens as electrical energy is transferred ( charge flows)

• electrons will move through conductor and collide with atoms in metal

• causes heating in wires so electrical energy will be transferred to thermal

examples of a conductor of electricity

metal

what are insulators

materials that don’t allow the flow of electrical charge

examples of insulator

plastic

resistance

how easy or difficult it is for electricity to flow / a measure how a component opposes the flow of electric charge

what does it mean if something has high resistance

hard for electricity to flow and has a low current

What is ohms law

Resistance = volts divide current

what does it mean if something has low resistance

easy for electricity to flow and has high current

current

the flow of electrons around a circuit

potential difference

a push around a circuit / the energy transfered or work done per unit of charge between two points in a circuit

when do resistors get hot

when current flows through them

what is heating effect caused by

collisions between moving charges and stationary atoms in wires

what does heating effect do

makes filament lamp hot enough to glow

why are metals good conductors

lots of free electrons to move

why are insulators bad conductors

don’t have free electrons to move

current equation

charge divide by time

time equation

charge divide by current

charge equation

current x time

what is potential difference

different in energy per unit of charge between 2 circuits

what happens in series circuit if u remove one component

current stops working so circuit stops

what happens to potential difference in series circuit

it is shared so total PD is all volts added together

In a series circuit describe relationship between resistance, pd,current

Current: same everywhere

Potential difference: shared between components so add voltage together

Resistance: add together

In a parallel circuit describe relationship between resistance, pd,current

Current: added together

Pd: same everywhere

Resistance: less then resistance of smallest resistor

How to connect ammeter in a circuit to measure current

Connect them in series with the component they are measuring current through

How to connect voltmeter in a circuit to measure potential difference

Voltmeter should be connected parallel to component they are measuring pd of

what is size of current determined by in series circuit

the total potential difference and resistance flowing

How to get total current in series circuit

It is the same everywhere

how to get total resistance in a series circuit

add all resistors together

when is current reduced

when resistor is added

what happens when u remove component in parallel circuit

circuit isn’t affected

what is potential difference like in a parallel circuit

it is the SAME everywhere

what happens to current in parallel

it is shared between components so add all together

what happens when u add resistor to parallel circuit

it reduces total resistance

how to get total resistance in a parallel circuit

total resistance is less than the resistor of smallest resistor

what is PD measured in

what is current measured in

what is resistance measured in

volts (V)

Amps (A)

Ohms (horse shoe)

equation linking pd, charge and energy transfer

pd= energy transferred divide by charge

what is charge measured in

Colombs (Q)

what is current

the flow of electric charge

what does greater charge mean in terms of current

greater current

when does charge flow

when there is potential difference

what does greater resistance of a component mean

smaller current for potential difference across a component

what is charge

the amount of charge flowing past a point in a circuit

what is resistance do to charge

slows charge flow down

what are components where current changes as resistance does

• filament lamp

• diode

what component does resistance not change as current changes

• ohmic conductors / resistors

what is rule about resistance in ohmic conductors

resistance doesn’t change as current changes because at certain temperatures current is directly proportional to the potential difference across it

What is an ohmic conductor

• a resistor

• A conductor where current and potential difference are directly proportional

• At constant temperatures resistance mains constant as current changes

List four components for which resistance is not constant as current changes

• FILAMENT LAMP

• LDR

• THERMISTOR

• DIODE

What happens to resistance if filament lamp as temperature increases and why

• resistance increases

• As at high temps Ions in wirel have more energy so more frequency of collisions with electrons and ions in current as flow through metal

• Causing greater resistance to current flow as need more energy for current to flow

What does the filament lamp graph tell us

• current and potential difference is not directly proportional - so resistance changes s current changes as

• Current will increase, increases temp of filament lamp which causes resistance to increase as lamp gets hotter (end of graph)

what happens in a filament lamp when it gets hot

causes resistance to increase which decrease current and causes lamp to glow

describe the trend in the filament lamp

• as the bulb gets hot the resistance increases which decreases current

• as potential difference increases, current begins to slowly no longer increase as more collisions in wire which causes wires to heat up increasing resistance

iwhat does resitance depend on diode

direction of current

which way does current flow diode and why

one direction because the diode has a high resistance in reverse direction so if it flows in direction of resistance it wom’t allow current to flow as high resistance

how are diodes useful

they can control the flow of current in circuit because in the forward direction the current will increase as potential difference increased

when does diode have high resistance

in reverse direction of current flowing

what does LDR depend on

light intensity

factors affecting LDR resistance and its use

1. increased light intensity = resistance decreases

2. decreased light intensity = resistance increases

3. USE: automatic night light

Give an LDR use and why is it used for this

Use: automatic night lights (street lamps

As when light levels become too low res they light gains current to turn light on as temp increases which causes light to turn on

And resistance will increase due to decreased light

factors affecting thermistor resistance and use

1. temperature increase = decreased resistance

2. 2 temperature decrease = resistance increase

3. USE: electronic thermostats

give two examples when a thermistor may be used

1. In thermostats - as temperature becomes too low resistance will increase causing a change in potential difference which circuit will detect causing heating to turn on. (Opposite if temp becomes to high)

2. In a freezer, when temp becomes too high resistance decreases along with potential difference (energy) in which the circuit detects , it then turns compressor on to cool the freezer down which will cause resistance to increase along with potential difference again.

earth wire

• green and yellow

• stops appliances coming live

• only carries current if fault

live wire

• brown

• provides alternating potential difference which is 230v

neutral wire

• blue

• completes circuit

• current flows through it

• 0v

what is alternating current

what is direct current

current that constantly changes direction

current always flowing in same direction

Uk mains supply voltage

230v

frequency AC mains supply

50h*2

why is live wire dangerous

if touch it a large potential difference is produced across wire which will produce a high amount of current flowing through you which can lead to electric shock

why is connection between live and earth wire dangerous

it creates low resistance path so current increases which transfers high heat energy which can result in a fire

what does national grid do

transfers electrical power from power stations all over grid in britain to where needed like homes

when is demand high for electricity

• when it’s dark

• when it’s cold

• when tv events are on

• when people are coming home from school or work

how do power stations cope with high demand

they often run below maximum power output so there is spare capacity to cope with higher demand

what does national grid have in terms of pd and current

low current, high potential difference

why does national al grid use low current and high pd

because high current requires a lot of energy and wires will heat up from high current making it transfer to thermal store which is wasted (inefficient)

why is national grid efficient

it uses high potential difference so there is a low current

• lower current means so less energy is wasted as heat

why does national grid use high pd

cheaper to boost than current and keeps low current

what does step up transformer do

potential difference increased as more turns in secondary coil than primary coil

what does step down transformer do

decreases potential difference as more turns on primary coil than secondary

Why do potentioal difference need to be decreased between transmission lines before passed into homes

• Lower potentials are safer for deomestic use and reduce likelihood of electrocution

• Appliances deigned for 230v

do appliances transfer all energy usefully and why

no as bigger current means more energy transfer to thermal store

what do electrical appliances do

transfer energy in circuit when current flows

what does total energy transferred in electrical appliances depend on

how long appliance has been on for and it’s power

what does it mean if an electrical appliance transfer transfers more energy in given time

it has a higher power

what happens if two insulators are rubber

electrons transfer from one insulator to the other and form positive on one and negatively charged ions on the other

what happens when conductors are rubbed

positive static charge on an object that loses electrons and negative static charge on an object that gains electrons

Describe energy transfers in a battery powered motor

• battery transfers chemical energy to electrical energy

• Motor converts electrical energy into kinetic energy aswell as waste energy to thermal store due to friction

Describe energy transfer in a battery powered torch

• battery converts chemical energy into electrical energy

• Bulb converts electrical energy into light aswell as waste energy in form of heating