measuring energy. electric current current: the rate of flow of electrons past a certain point in a...
TRANSCRIPT
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 Resistance
1. Type of Material: some materials have less internal resistance than others
Factors Affecting Resistance
1. Type of Material: some materials have less internal resistance than others
Insulators: resist the flow of electrons
Factors Affecting Resistance
1. Type of Material: some materials have less internal resistance than others
Insulators: resist the flow of electrons
e.g. air plastic
Factors Affecting Resistance
2. Length: the longer a wire is, the more electrical resistance the wire has
Factors Affecting Resistance
2. 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 Resistance
3. 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 Resistance
4. Temperature: as temperature increases, its electrical resistance increases
e.g. solenoid switches and furnace igniters
Factors Affecting Resistance
4. Temperature: as temperature increases, its electrical resistance increases
e.g. solenoid switches and furnace igniters
-if igniter heats up, its resistance increases
Factors Affecting Resistance
4. Temperature: as temperature increases, its electrical resistance increases
e.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