MEASURING ENERGY

Electric Current

Electric Current Current: the rate of flow of

electrons past a certain point in a circuit

Electric Current

Current: the rate of flow of electrons past a certain point in a circuit Current = Counting electrons

Electric Current

Current: the rate of flow of electrons past a certain point in a circuit Current = Counting electrons

Ampere (A): the unit of electric current

Electric Current

Current: the rate of flow of electrons past a certain point in a circuit Current = Counting electrons

Ampere (A): the unit of electric current

e.g. a 15A breaker opens the circuitwhen there are 15A of electrons flowing throughthe wires

Electric Current Current: the rate of flow of

electrons past a certain point in a circuit Current = Counting electrons

Ammeter: a device used to measure current

Electric Current Current: the rate of flow of

electrons past a certain point in a circuit Current = Counting electrons

Ammeter: a device used to measure current -an ammeter is always placed in

series

Electric Current Current: the rate of flow of

electrons past a certain point in a circuit Current = Counting electrons

Ammeter: a device used to measure current -an ammeter is always placed in

series

Electric Current

Which scale do you read?

Electric Current

Which scale do you read?

Electric Current

Estimate the reading:

Electric Current

Estimate the reading: between 150 and 200

Electric Current

Estimate the reading: between 150 and 200What is each marking worth?

Electric Current

Estimate the reading: between 150 and 200What is each marking worth? 5

Electric Current

Estimate the reading: between 150 and 200What is each marking worth? 5Final Answer?

Electric Current

Estimate the reading: between 150 and 200What is each marking worth? 5Final Answer? 175

Electric Current

Which scale do you use?Estimate the reading: between?What is each marking worth? Final Answer?

Electric Current

Which scale do you use?Estimate the reading: between?What is each marking worth? Final Answer?

Electric Current

Which scale do you use?Estimate the reading: between? 20 and 40What is each marking worth? Final Answer?

Electric Current

Which scale do you use?Estimate the reading: between? 20 and 40What is each marking worth? 2Final Answer?

Electric Current

Which scale do you use?Estimate the reading: between? 20 and 40What is each marking worth? 2Final Answer? 32

POTENTIAL DIFFERENCE

Potential Difference Potential Difference (voltage):

the difference in electrical potential energy between two points in the circuit

Potential Difference Potential Difference (voltage):

the difference in electrical potential energy between two points in the circuit

Volt (V): the unit of potential difference

Potential Difference Potential Difference (voltage):

the difference in electrical potential energy between two points in the circuit

Volt (V): the unit of potential difference

Voltmeter: a device used to measure potential difference

Potential Difference Potential Difference (voltage):

the difference in electrical potential energy between two points in the circuit

Volt (V): the unit of potential difference

a voltmeter has to be connected in a parallel circuit

Potential Difference

looks like this...

Potential Difference

looks like this...

Potential Difference

an analogy: the waterfall

Potential Difference

an analogy: the waterfall

Current: number of electrons

Potential Difference

an analogy: the waterfall

Current: number of electrons=amount of water

Potential Difference

an analogy: the waterfall

Current: number of electrons=amount of water

Potential Difference: energy of the electrons

Potential Difference

an analogy: the waterfall

Current: number of electrons=amount of water

Potential Difference: energy of the electrons

=height of the waterfall

RESISTANCE

Resistance Resistance: the ability of a

material to oppose the flow of electrons through it

Resistance Resistance: the ability of a

material to oppose the flow of electrons through it

Ohm (Ω): the unit of electrical resistance

Resistance Resistance: the ability of a

material to oppose the flow of electrons through it

Ohm (Ω): the unit of electrical resistance

Ohmeter: a device used to measure electrical resistance

Factors Affecting Resistance

Factors Affecting Resistance1. Type of Material: some

materials have less internal resistance than others

Factors Affecting Resistance1. Type of Material: some

materials have less internal resistance than others

Insulators: resist the flow of electrons

Factors Affecting Resistance1. Type of Material: some

materials have less internal resistance than others

Insulators: resist the flow of electrons

e.g. air plastic

Factors Affecting Resistance2. Length: the longer a wire is,

the more electrical resistance the wire has

Factors Affecting Resistance2. Length: the longer a wire is,

the more electrical resistance the wire has

High voltage transmission lines: are used so fewer electrons have to travel through wires travelling long distances

Factors Affecting Resistance3. Thickness: a thick wire has less

electrical resistance than a thin one.

e.g. extension cords shouldn't be used permanently because they are usually thinner wires and can overheat

Factors Affecting Resistance4. Temperature: as temperature

increases, its electrical resistance increases

e.g. solenoid switches and furnace igniters

Factors Affecting Resistance4. Temperature: as temperature

increases, its electrical resistance increases

e.g. solenoid switches and furnace igniters

-if igniter heats up, its resistance increases

Factors Affecting Resistance4. Temperature: as temperature

increases, its electrical resistance increasese.g. solenoid switches and furnace igniters-if igniter heats up, its resistance increases-solenoid opens and gas is released & furnace lights

OHM’S LAW

Ohm’s Law In 1827, Georg Ohm noticed a

relationship between current, potential difference and resistance

After many experiments he noted that: For a given resistance, as the

electric potential difference across a load increases, so does the current

Ohm’s Law Ohm’s Law- the relationship

between resistance, current and potential difference.

For a given potential difference, as the resistance increases, the current decreases

Another way to look at resistance.. The flow of electrons can be compared

to people running an obstacle course More obstacles= runners moving slower

through the course

Wider course=more runner able to go through at the same time

Electron flow link The amount of resistance in a circuit

affects the amount of current(electrons) that can flow through it More obstacles, slower flow of electrons Wider= more electrons can flow through # of loads= more loads means more

resistance

Factors that can increase resistance Connecting more loads in series Connecting loads in series rather than

parallel Making the conductor longer Making the conductor thinner Using material with a high resistance

Ohm’s formula