Thursday, November 18, 2004

Lesson 16, 17

ELECTRICITY LESSON 16 – Current
Lesson: 16.
Take up Hwk: Hand back quiz
Text pg. 314 Current, c.p. pg. 69
Lesson: Current
Current Overhead
Current Worksheet: Here
Lab investigation: build a simple series circuit and a simple parallel circuit
Homework: Complete worksheet and pg. 315 text #1-4

Overhead of Current Lesson:

Electricity is a term used to describe the energy produced (usually to perform work) when electrons are caused to directional (not randomly) flow from atom to atom. In fact, the day-to-day products that we all benefit from, rely on the movement of electrons. This movement of electrons between atoms is called electrical current.


Electricity current is the rate at which electricity flows through a circuit, to transfer energy. Current is measured in Amperes ("A"), commonly called Amps. Analogy: Flow rate in a water pipe.


It was not until 1600 that a man named Dr. William Gilbert coined the term “electrica,” a Latin word which describes the static that occurs when amber and other materials are rubbed.

THE LAW OF CONSERVATION OF CHARGE
1. THE LAW OF CONSERVATION OF CHARGE STATES THAT AN ELECTRIC CHARGE CANNOT BE CREATED OR DESTROYED.





DC CURRENT
As long as electrons are flowing through the atoms of the circuit, work is being done. We can see that work is being done in this circuit because it lights the light bulb. The actual amount of electrons that are flowing is determined by the type and size of the battery as well as by the size and type of the light bulb. We could reverse the polarity of the battery by switching the contacts (wires), and the current would flow in the opposite direction and the bulb would still light.Either way the battery is connected to the circuit, current can only flow in one direction. Direct current (DC) can also be generated by means other than batteries. Solar cells, fuel cells, and even some types of generators can provide DC current.


AC CURRENT
AC is short for alternating current. This means that the direction of current flowing in a circuit is constantly being reversed back and forth. This is done with any type of AC current/voltage source.
The electrical current in your house is alternating current. This comes from power plants that are operated by the electric company. Those big wires you see stretching across the countryside are carrying AC current from the power plants to the loads, which are in our homes and businesses. The direction of current is switching back and forth 60 times each second.


ELECTRIC CURRENT WORKSHEET

P.314-315
1. What is electric current? What type of charge moves through a circuit?
2. What do the protons do in an electric current?
3. Electric current is a measure of what? What are the units for electric current?
4. Current is measured with what instrument connected to the circuit in series?
5. What is the difference between static and current electricity?
6. The larger the current, what happens to the muscles in the human body?
7. What happens to muscle cells when electric current flows through them?
8. When does muscle contraction cease in a person?
9. What current is needed to feel a tingling sensation?
10. What is the value for the “let-go” threshold? What happens at the “let-go” threshold? Explain.
11. What happens if the current going through a person’s chest is 0.050 A or more?
12. How do you stop ventricular fibrillation?
13. What type of currents are needed to cause severe burns?
14. Before helping a victim of electric shock, what are some precautions that you need to do?


ELECTRICITY LESSON 17 – Measuring Voltage Lab
Lesson: 17.
Take up Hwk: Complete worksheet and pg. 315 text #1-4
Lab c.p. pg. 72 -74 (hand in questions – 2 marks per question)
Hwk: Complete lab at home to be completed no later than tomorrow must also include the worksheet calculations


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