Download - Chapter 16 Electricity
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Chapter 16Electricity
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The Electric Motor
• Electric motors convert electricity into motion!
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How a Motor works!
• Electric motors operate according to the law of magnetic poles
• Unlike poles attract!• Like poles repel!
• A simple motor has an electromagnet mounted on a shaft to freely rotate!
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How an Electric Motor Works!
• The electromagnet and shaft are placed between poles of a field magnet used to provide a stationary magnetic field!
• The force of attraction and repulsion cause the armature (electromagnet) to rotate and spin!
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Electric Current
• Electrons are in motion!• When a lightning strike hits the earth, a
massive current of electricity flows to the earth!
• The flow of electrons is electricity!• If the electrons are at rest, it is static
electricity!
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DC and AC Current
• Current electricity can be subdivided into either of two types depending on how it flows!
• If it flows in one direction, it is direct current (DC).
• If it flows in one direction and then another, it is alternating current (AC).
• AC is used in our homes because it can be transmitted over long distances.
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Causes of Electric Flow
• Electrons move from one place to another!• This is a result of attraction and repulsion.• They will flow from negative to positive…
like with a battery!
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Voltage
• The greater the difference between two charges – the more negative and positive they are – the stronger the force that drives the flow!
• The difference between charges determines voltage.
• Voltage is also called “electric potential”.• The SI unit of voltage is Volt (V)• A device that measures voltage is a voltmeter!
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Amperage
• Amperage refers to the volume of flow of current!
• The unit of electric current is ampere (A)• It is one coulomb per second!• Remember – it is a RATE of flow!• A device that measures current is an
ammeter!
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Power• Power is the amount of
voltage times the amount of amperage.
Power = voltage X amperage
P=VI“I” represents amperage
• The unit for power is the Watt (W).
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Resistance
Conductors and Insulators
Electric current flows through some materials much more easily than it flows through others.
Materials through which current flows easily are called conductors.
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Resistance
Conductors and Insulators
Materials through which current does not easily flow are called insulators.
They are called insulators because they can be used to insulate objects from electric current.
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Resistance
• The amount by which a material hinders the flow of electrons is called resistance.
• The unit for resistance is the ohm!
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factors which increase resistance
1. Type of material2. Diameter of the conductor – thick wire
has less resistance3. Length of the conductor – the longer the
more resistance4. Temperature – higher temperature
creates more resistance
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Ohm’s Law• There is a mathematical
relationship between current and resistance.
• This relationship is called Ohm’s law.
• Current is directly proportional to voltage and inversely proportional to resistance.
V = I X R
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Ohm’s Law
• V is the voltage in volts • I is the current in amperes or amps • R is the resistance in ohms • IR is I times R
• The unit for resistance is the Ohm (Ω)
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Ohm’s Law
Problem #1
A small electrical pump is labeled with a rating of 3 amps and a resistance of 40 ohms. What voltage was it meant to run at?
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Ohm’s Law
Problem #2
A nine volt battery is hooked up to a light bulb with a rating of three ohms. How much current passes through the light?
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Ohm’s LawProblem #3
A lamp is plugged into the wall outlet, which is providing 110 volts. An ammeter attached to the lamp shows 2 amps flowing through the circuit. How many ohms of resistance is the lamp providing?
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Ohm’s Law
Current and voltage are directly related.↓↓ ↑↑
Current and resistance are inversely related.↓↑
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Limiting Current
• A resistor is a device used to limit the flow of electricity.
• Resistors are used to protect delicate electrical components that cannot handle large currents!
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Electric Circuits• The path current follows is
the electric circuit.
• A simple electric circuit contains three parts:1. battery or generator2. conductor (wire)3. load (uses the current – ex: bulb)
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Closed and Open Circuits
• Electric current requires a complete circuit in order to flow!
• A circuit is a closed circuit if the electrons can flow in a complete path back to the source.
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Closed and Open Circuits
• An open circuit has a gap and so the current cannot flow!
• Often times the gap is created with the use of a switch!
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Circuit Arrangements
• Simple circuits contain only one load (one Bulb).
• More complex circuits have multiple loads.• For this reason, a circuit can be arranged
in two basic ways:– In series– In parallel
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Series Circuit• In series circuits, the loads are
arranged so that the electric current flows through each load one after the other.
• The current must pass through each bulb to get to the next.
• If one bulb (load) blows out, the circuit is now open and the current cannot flow.
• Also, due to the resistance being cumulative, the current is reduced from one bulb to the next and so they do not burn as brightly.
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Series Circuit
• If switch 1 and 2 are closed, the bulbs will light up.
• If switch one is open. Both bulbs will go out.
• If switch 2 is open, both bulbs will go out.
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Parallel Circuits• In parallel circuits, loads
are arranged in separate branches of the circuit and the current is divided among them.
• Parallel circuits have the same amount of current flowing through each load!
• If one load blows out the rest of the loads will continue to receive current and remain active!
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Parallel Circuits• If all three switches are closed
then the bulbs will light up. • If switch 2 is open then only
bulb a will go out. Current is still flowing through bulb b so it will stay on.
• If switch 3 is open then only bulb b will go out. Current is still flowing through bulb a so it will stay on.
• If switch 1 is open, all the bulbs will go out.
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Drawing Circuits
• When drawing circuits, symbols are used to signify various components.
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The End