Chapter 7. Protons = positive charge Electrons = negative charge Most atoms have the same number...
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Transcript of Chapter 7. Protons = positive charge Electrons = negative charge Most atoms have the same number...
Positive and Negative Charges
Protons = positive charge Electrons = negative charge
Most atoms have the same number of protons and electrons and thus will have no net charge. Atoms become charged when they gain or
lose electrons.
Electricity obeys rules???
Law of conservation of charges - Charges can be transferred from object to object, but cannot be created or destroyed.
Opposite charges attract, like charges repel.
electrons move easier through conductors ex. metals
Electrons do not move easy through insulators ex. plastic, wood, rubber, and glass
Transferring Electric Charge
Charging by contact process of transferring charge by touching or
rubbing Ex. Static electricity from rubbing your feet on
carpet Charge by induction
the rearrangement of electrons on a neutral object caused by a nearby charged object Ex. a negatively charged balloon near your
sleeve causes an area of your sleeve to become positively charged
Transferring Electric Charge
Static discharge A transfer of charge through the air b/w two
objects because of a buildup of static electricity
Ex. Lightning
Read Page 197 Write and Answer the following questions
1. When the warm humid air rises to meet the cold air, what causes the air masses to churn together?
2. What electric property causes the negative charges in the cloud to be attracted to the positive charges in the ground?
3. Why does the ground below a cloud have a concentration of positive charges?
Electric current
The flow of charges through a conductor (like a wire) is called electric current. Usually the flow of electrons Measured in Amperes (A) Flow from high to low voltage.
A voltage difference is the push that causes charges to move.
Voltage difference is measured in volts (V).
Circuit
For charges to flow, the wire or conductor must always be connected in a closed path called a circuit.
Sources of Electricity
Dry cell battery - produces voltage difference b/w its zinc container and its carbon suspension rod, causing current to flow b/w them
Wet cell battery – contains two connected plates made of different metals in a conducting solution.
Wall sockets – have a voltage difference across the two holes of an electrical outlet, and a generator at a power plant provides this voltage difference
Resistance
The tendency for a material to oppose the flow of electrons, changing electrical energy into thermal energy and light. All materials have some electrical resistance.
Measured in ohms (Ω) Making wires thinner, longer, or hotter
increases the resistance.
Ohms Law
Example Problem #1: What is the current in a 30V circuit if the resistance is 6Ω?
current (in amperes) = voltage difference (in volts)
resistance (in ohms)I = ?V = 30VR = 6Ω
Ohms Law
Example Problem #2: An Ipod uses a standard 3.7 V battery. How much resistance is in the circuit if it uses a current of 0.025 A?
current (in amperes) = voltage difference (in volts) resistance (in ohms)
I = V/R
Series Circuit
Series circuit - The current only has one loop to flow through Parts of the circuit
are wired one after another, so the amount of current is the same through every part
Ex. String of holiday lights
Parallel Circuit
Parallel circuit – contains two or more branches for current to move through Parts can be
turned off without affecting the entire circuit
Ex. the electrical system in a house
Household Circuits
Parallel circuits connected in a logical network.
Electric energy enters your home at the circuit breaker or fuse box and branches out to wall sockets, lights, and major appliances
Guards against overheating Electric fuse Circuit breaker
Electrical Energy
Electrical energy is easily converted to thermal, radiant or mechanical energy. Electrical power – the rate at which electrical
energy is converted to another form of energy Electrical power is expressed in watts (W). Power = current X voltage difference P(watts) = I (amperes) X V (volts)
Example Problem
Your microwave runs at a current of 10 amps. A standard plug in your house has a voltage difference of 120 volts. How much electrical power does it take to run this appliance?
P = I x V