physics 2

electricity

what is current

a flow of electric charge

what is potential difference

the driving force that pushes the charge round

what is resistance

anything that slows the flow down

what is the equation for charge flow

charge flow (Q)= current(I) x time(s)

what is the equation for potential difference

p.d(V) = current x resistance

what are 2 things the resistance can depend on

• if it is in series or parallel

• wire length

what does the ammeter measure and where must it be placed

measures current and must be placed in series with what you are measuring

what does the voltmeter measure and where must it be placed

measures potential difference and must be placed in parallel with what you are measuring

what can you say about the current and the potential difference in an ohmic conductor

they are directly proportional

identify this graph

ohmic conductor

identify this graph

filament lamp

identify this graph

diode

what is an LDR

Light Dependent Resistor

in what condition is a thermistor at its highest resistance

cold

what are sensing circuits

can be used to turn on or increase power to components depending on the conditions they are in.

what is a series circuit

all the different components are connected in a line, end to end except for voltmeters which are always connected in parallel

in a series circuit what happens to the

1. potential difference

2. current

3. resistance

1. p.d is shared - the p.d always adds up to the source of p.d

2. current is the same everywhere

3. resistance adds up

what is a parallel circuit

each component is separately connected to the supply

in a parallel circuit what happens to the

1. potential difference

2. current

3. resistance

1. p.d is the same across all components

2. current is shared between branches

3. adding a resistor in parallel reduces the total resistance

what are the 2 types of electric supply

• alternating

• direct current

what are the 3 wires found in a cable called

• neutral wire

• live wire

• earth wire

describe the neutral wire

• BLUE

• completes the circuit , current flows through the wire. it is around 0V

describe the live wire

• BROWN

• provides alternating potential difference (230V)

describe the earth wire

• GREEN and YELLOW

• stops the appliance casing from becoming live.

• doesn’t usually carry a current - only when there is a fault

what’s the 2 equations for energy transferred

1. E.T = power x time

2. E.T = charge flow x P.D

whats the equation for power

Power = P.D x current

what is the national grid

a giant system of cables and transformers that covers the uk and connects power stations to consumers

what do transformers do

step-up transformer increases P.D