Download ICP Chapter 7: Electricity

ICP Chapter 7: Electricity
Vocabulary
1 charging by contact; 2 charging by induction; 3 circuit; 4 conductor; 5 electric current; 6 electrical
power; 7 insulator; 8 kilowatt-hour; 9 law of conservation of charge; 10 Ohm’s law; 11 parallel circuit;
12 resistance;13 series circuit; 14 static electricity; 15 voltage difference;
** EXTRA** 16 grounding;17 electroscope
1. Process of transferring charge by touching or rubbing
2. The rearrangement of electrons on a neutral object caused by a nearby charged object
3. A closed conducting path
4. Material through which excess electrons can move more easily
5. The flow of charges through a wire or any conductor
6. The rate at which electrical energy is converted into another form of energy; P = I V = watts
7. Material that does not allow electrons to move through it easily
8. Unit of electrical energy = 1,000 watts of power used for 1 hr; (kWh)
9. Charge can be transferred from object to object, but it cannot be created nor destroyed.
10 The current in a circuit equals the voltage difference divided by the resistance: V = I R= A .
11 Electric current containing > 2 branches through which current can flow
12 The tendency for a material to oppose the flow of electrons, changing electrical energy into thermal
energy and light; is measured in ohms (.
13 An electric current with only a single loop through which electrons flow
14 The accumulation of excess electric charges on an object
15 The push that causes electric charges to move; is measured in volts (V).
16 Connecting an object to Earth with a conductor
17 A device that can detect the presence of electric charges
Main Ideas
I. Electric Charge
A. Static Electricity
1. Accumulation of excess electric charges on an object
a. Can damage electric equipment
b. Can kill humans
2. Electrons have negative charges; protons have positive charges.
a. Oppositely charged particles attract; like charges repel.
b. An electric field surrounds every charge & exerts a force on other charges.
3. Charge is conserved
a. Law of conservation of charge: lost charges = gained charges
b. Charges can be transferred but not created nor destroyed.
B. Conductors & Insulators
1. Conductors allow excess electrons to move more easily through them than others.
a. Metals are excellent conductors of electricity: Cu, Au, Ag, etc…
b. Your skin is a good conductor too.
2. Insulators don’t allow electrons to move easily through themselves.
a. Most plastics are good insulators.
b. Wood, rubber, and glass are also good insulators.
C. Transferring Electric Charge
1. By contact
a. Rubbing or touching 2 objects together can result in electrons to transfer.
b. Socks from the dryer; combing hair on dry day; scooting wool socks on carpet
2. At a distance
a. Electrical forces can act at a distance, such that a charged object can cause
electrons on neutral objects to rearrange their position on the neutral one
3. Lightning
a. Thunderclouds are might generators of static electricity. As air masses swirl in
clouds, have build up of areas of (+) & (-) charges. As charges move through
air, they collide with atoms & molecules  sparks
b. It’s estimated Earth is struck by lightning > 100 times a second!!!
4. Thunder
a. Electrical energy in lightning bolts rips electrons off atoms in the atmosphere,
producing heat (~25,000 oC), causing rapid expansion of nearby air thunder
5. Grounding
a. Earth is a large neutral object that is also a conductor of charge.
D. Detecting Electric Charge
1. Electroscopes detect electric charges.
a. When there is no charge, the 2 metal leaves hang down, parallel to each other.
b. When charged, the leaves both get same charge & therefore repel each other.
II. Electric Current
A. Charge on the Move
1. Electrical pressure
a. Charges flow from high-voltage to low-voltage areas.
b. Voltage difference is the push moving charges & is measured in volts (V).
2. Closed circuits
a. Circuits must be a closed, conducting path.

Series – have only a single loop; used in flashlights & holiday lights

Parallel – have > 2 branches of the same voltage difference; used in
household wiring – branch out from the fuse or breaker box
b. Fuses protect against overheating (excess current) by allowing wire to melt.
c. Circuit breaker has metal that bends when hot, causing switch to flip.
d. Electric current (the flow of electrons) is measured in amperes (A).
3. Batteries
a. Dry-cell – Zinc container surrounds moist chemical paste with a center solid
carbon rod. Chemical rxns in the paste transfer electrons to the Zn container.
The C rod becomes (+) and the Zn becomes the (-) terminal.
b. Wet-cell – Contains 2 connected plates made of different metals or metallic
compounds in a conducting solution. Car batteries with 6 wet cells made up
lead and lead dioxide plates is a sulfuric acid solution. Each cell has voltage
difference of ~2 volts, yielding a total 12 V. Alternators reverse the charges.

4. Voltage differences
a. Wall outlets in the USA have a voltage difference of 120 V across the 2 holes.
b. Europe & some US outlets have a voltage difference of 240 V.
B. Resistance
1. Measured in ohms (); the tendency to oppose the flow of electrons
2. Conductors have low  & therefore Cu’s used for house wiring because has < heat.
3. Tungsten wire has high  so is used for light bulb filaments  glows white-hot.
4. Thinner wires have > longer wires have > ; as temperature increases, so does 

Ohm’s Law: V = I R; voltage difference = current x resistance; v =A amps(ohms)
C. Electrical Power
1. Electrical energy is converted to many other types of energy: thermal, light,
mechanical, sound, etc…
2. Watts = electrical power – rate of conversion of electrical energy into other forms
a. Power = current x voltage difference; P watts = (I amperes)(V volts)
b. Power rating is label found on appliances indicating amount of power it uses.
D. Electrical Energy
1. The amount of energy used by a device is found by multiplying power x time.
a. Energy = Power x Time; E kilowatt hours = P kilowatt x t hour
b. Kilowatt hour = 1000 watts of power used for 1 hour
2. Energy cost $ and valuable natural resources such as coal, petroleum, or natural gas.