electricity: the mouse and cheese analogy all matter is made up of positive charges and negative...
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Electricity: The Mouse and Cheese Analogy
• All matter is made up of positive charges and negative charges. – The positives have mass and are not usually
free to move. – The negatives have no mass and are free to
move through some materials (conductors).
Mouse and Cheese Analogy• Negative charges are attracted to
positive charges the same way mice are attracted to cheese. – Any time there is a natural attraction between two
things we can use it to make the objects do work. – The negative charges (mice) will gladly do work in
order to get to the positive charges (cheese).
Electric Current• Continuous flow of electric charge.– SI unit of electric current is the AMPERE (A) or amp.– 1 amp = 1 coulomb per second.
• Two types of electric current:– Direct Current (DC)– Alternating Current (AC)
Mouse and Cheese Analogy• Current: –The number of charges (mice) passing a point
per second. The rate of flow of charges.
Direct Current• DC• Charges flow in
one direction.–Most battery
operated items use DC.
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Alternating Current• Flow of electric charge that regularly
reverses its direction.Most electric current at home and school.
Dotted lines are from AC
Conductor and Insulator• Electrical Conductor– Material through which charge
can flow easily.• Copper and Silver
• Electrical Insulator– Coating around a wire that
controls the current and keeps it where its needed.• Wood, plastic, air Rubber
Insulating Material(plastic)
Conducting Wire(copper)
Superconductor• Material that
has almost zero resistance when cooled to low temperatures.– Best superconductors
must be cooled to 138K.
Resistance• Opposition to the flow of charges in a
material.– SI unit of resistance is ohm (Ω).
• Four factors affect the resistance in a wire:– Material type– Thickness– Length– Temperature
Mouse and Cheese Analogy• Resistance: • The opposition to the flow of charge. • Any appliance that asks the charge (mouse) to
do work will slow it down.
Voltage• The difference of electrical
potential between two points of an electrical circuit.• Also called the potential difference.– SI unit for voltage is a VOLT – One volt = one joule per coulomb
• Voltage: –The amount of work that each charge
(mouse) will do as it goes through the circuit. –Can also be thought of as
the amount of push on the charges or how hungry the mice are.
Mouse and Cheese Analogy
Voltage Sources• Three common voltage sources:–Battery–Solar Cell–Generator
Battery• Device that converts chemical
energy to electrical energy
Ohm’s Law• Georg Ohm (1789-1854)– Found a relationship between voltage, current,
and resistance.
• Ohm’s Law:– The voltage (V) in a circuit equals the product of
the current (I) and the resistance (R).– V = I x R I = V R = V
R I
ELECTRICAL CIRCUITSChapter 20.3
Circuit Diagrams• Use symbols to represent parts of
a circuit.• Include:– Sources of electrical
energy– Devices that are run by electrical
energy
TYPES OF CIRCUITS
Series Circuits• Charge has only ONE path through
which it can flow.• If one element stops functioning in a
series circuit, NONE of the elements can operate.–The bulbs in a circuit are a source of
resistance. The more bulbs, the more resistance.
Parallel Circuit• Charge has TWO OR MORE
paths through which the charge can flow.• If one element stops
functioning, the rest of the elements can still operate.