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Measuring Energy

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Electric Current

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

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

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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

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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 circuit when there are 15A of electrons flowing through the wires

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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

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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

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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

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Electric Current Which scale do you read?

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Electric Current Which scale do you read?

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Electric Current Estimate the reading:

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Electric Current Estimate the reading: between 150 and 200

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

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

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

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

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

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

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

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

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

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Potential Difference

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Potential Difference Potential Difference (voltage): the difference in electrical potential energy between two points in the circuit

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Potential Difference Potential Difference (voltage): the difference in electrical potential energy between two points in the circuit Volt (V): the unit of potential difference

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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

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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

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Potential Difference looks like this...

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Potential Difference looks like this...

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Potential Difference an analogy: the waterfall

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Potential Difference an analogy: the waterfall Current: number of electrons

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Potential Difference an analogy: the waterfall Current: number of electrons =amount of water

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Potential Difference an analogy: the waterfall Current: number of electrons =amount of water Potential Difference: energy of the electrons

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Potential Difference an analogy: the waterfall Current: number of electrons =amount of water Potential Difference: energy of the electrons =height of the waterfall

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Resistance

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Resistance Resistance: the ability of a material to oppose the flow of electrons through it

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Resistance Resistance: the ability of a material to oppose the flow of electrons through it Ohm (Ω): the unit of electrical resistance

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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

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**Factors Affecting Resistance**

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**Factors Affecting Resistance**

1. Type of Material: some materials have less internal resistance than others

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**Factors Affecting Resistance**

1. Type of Material: some materials have less internal resistance than others Insulators: resist the flow of electrons

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**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

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**Factors Affecting Resistance**

2. Length: the longer a wire is, the more electrical resistance the wire has

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**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

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**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

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**Factors Affecting Resistance**

4. Temperature: as temperature increases, its electrical resistance increases e.g. solenoid switches and furnace igniters

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**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

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**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

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Ohm’s Law

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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

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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

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**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

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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

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**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

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Ohm’s formula

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