Physics-Topic 2 Electricity

What are ohmic conducters?

Components that follow ohms law

Frequency of Uk mains?

50 Hz

What is current?

The flow of particles (called electrons) though wires and components

Potential difference of uk mains?

230v

What is current measured in?

Amps

What is potential difference?

A measure of the amount of energy needed to move a charges

What is P.D measured in?

Volts

What is resistance?

A measure of the difficulty of passing an electric current through a conducting material

What is resistance measured in?

Ohms

Ohms law?

At a constant temperature, for a fixed resistor, the potential difference across it is directly proportional to the current through it

What is the current and voltage like in series circuits?

Current is the same and voltage is shared

What is the current and voltage like in parallel circuits?

The current is shared but the voltage is the same

Ohmic conductor example?

Fixed resister at constant temp

How does a light bulb work?

Current goes through a filament which heats up and glows, non-ohmic conducter

What is the correlation between temperature and resistance in light bulb?

When the temp increases so does the resistance

What are diodes?

Non-ohmic conducter, only let current flow one way, the resistance is constantly changing

What is the corralation between a current and resistance and current in a diode?

When the current decreases the resistance increases

What is a thermister?

A resister made of semiconductors with a resistance that varies with temp

What is the link between temp and resistance in a thermistor?

The higher the temp the lower the resistance

What is the link between light and resistance in an LDR?

When light shines on it the resistance varies, resitance decreases as light increases

What is the rule about total resistance in Parralel circuits?

• total resistance is always less than the smallest individual resistor

Relationship between current and resistance in parralel?

Inversely proportional

What is a D.C?

• direct current

• Only flows in one direction forever

• E.g. cells and batteries

What is A.C?

• alternating current

• Current constantly change direction

• E.g mains like lights and plugs

• In uk it switches 50 times a second , uk frequency is 50Hz

Graph for alternating current?

Graph for direct current?

What is the national grid?

A national network of high voltage cables and transformers

Order of the national grid?

• power station

• Step up transformers

• Pylons

• Step down transformers

• Industry

• Homes

What do step up transformers do and why?

• raises the P.D from 12,000 volts to 400,000 volts

• This reduces the current and so reduces the thermal energy transfer

• Making the transmission more efficient

What do step down transformers do?

• reduce voltage down to 230V so it can be used in homes safely

Live wire

Brown

Volts 230, provides alternating potential difference

Neutral wire

Blue

Completes circuit , current flows through live and neutral

0v

Earth wire?

• 0v

• Green and yellow

• Safety

• Carries current to ground if there is a fault

Fuse?

• safety measure

• Melts if the current is too string

What is static electricity?

• friction between rubbing surfaces that causes a transfer of electrons

When does static electricity work?

• only word on insulation materials as conducted (e.g metals) have a sea of delocalised electrons and so can just replace any lost electrons