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I. . is a force defined as the movement of negatively charged electrons. A. Types of Electricity. 1. Static is not moving. An example of this would be a person rubbing his feet against carpet and touching a conductor. What is a conductor? A conductor is something
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I. is a force defined as the movement of negatively charged electrons.
A. Types of Electricity • 1. Static is not moving. • An example of this would be a person rubbing his feet against carpet and touching a conductor. • What is a conductor? • A conductor is something that allows electricity to flow.
a. Lightning • Why do we see lightning before we hear thunder? • Since light and sound travel at different speeds, we see the lightning before we hear the thunder. They occur at the same time, however.
2. Current Electricity • Also known as moving or electric energy. • Electricity needs a force to push the electrons into a flow (batteries or generators).
II. Conductors vs. Insulators • Conductors allow electricity to move through them. • Insulators do not allow electricity to move through them. • Give an example of a conductor. • Copper, water, and aluminum are good conductors. • Give an example of an insulator. Plastic, wood, and glass are insulators,
Which is best to hold if I am heating a liquid in a metal pan?
A. Current • Current is the amount of electrons passing through an area at one time. • It is measured in Amps. • Current may be direct (DC) or alternating (AC). • Alternating current moves in one direction and then moves in the opposite direction, switching back and forth in direction.
Direct Current • If an alternating current switches directions, how does direct current move?
Why have two types of current? • It allows us to transport energy more efficiently over a greater distance.
B. Resistance • This is the force NOT allowing electrons to move easily. • It is measured in Ohms. • Question: Something with a low resistance is a good conductor. True or false? • Give an example of a conductor.
1. Insulators • An insulator does NOT allow electrons to move through it easily. • We use copper as a conductor in our electrical plugs.
Insulators • Electrical plugs are coated with an insulator. • What is the insulator? • Why is it needed? Electrical plugs are coated with an insulator. What is the insulator? Why is it needed?
III. How do we get electrons moving? • Forces that start the flow of energy: • Batteries can do this. • They store chemical energy. • One end of the battery contains extra electrons (so it will have what type of charge?) • The opposite end of the battery has too few electrons (so it will have what type of charge?)
A. Units of Energy • Amps = Current is the amount of electrons passing through an area at one time. • Ohms = Resistance or the force not allowing electrons to move. • Watt = energy used per second • Voltage = Current (I) x Resistance (R)
Resistance • Human body has a resistance of 500,000 Ohms if dry. • Human body has a resistance of 100 Ohms if wet. • Salt lowers resistance even more. • Why is it not a good idea to be in a tub during a thunder storm?
Why is this not a good place to be during a lightning storm? • The chance of electrocution is increased drastically. • The tub may also be connected to a metal pipe that runs to the ground.
B. Circuits are the paths for electrons: 2 types • Series – all energy flows through the same path (like x-mas lights, if one goes out they all go out) • Parallel – energy flows to each bulb (like in your homes)
When you flip a light switch, you complete the circuit. • The electrons (chemical energy) are sent through a light bulb (which has a high resistance) and heat energy is produced. • Heat energy changes to light energy.
What’s in your bulb? • At the bulb base, bulbs have two metal contacts, which connect to the ends of an electrical circuit. • The metal contacts are attached to two stiff wires, which are attached to a thin metal filament. The filament sits in the middle of the bulb, held up by a glass mount. • The wires and the filament are housed in a glass bulb, which is filled with an inert gas, such as argon.
Moving current… • When the bulb is hooked up to a power supply, an electric current flows from one contact to the other, through the wires and the filament.
How do electrons move??? • As the electrons zip along through the filament, they are constantly bumping into the atoms that make up the filament. The energy of each impact vibrates an atom -- in other words, the current heats the atoms up. • It’s almost like a domino effect. One atom moves, so another moves, and another, and so on.
What are photons? • Bound electrons in the vibrating atoms may be boosted temporarily to a higher energy level. When they fall back to their normal levels, the electrons release the extra energy in the form of photons. • Metal atoms release mostly infrared light photons, which are invisible to our eyes. • But, if they are heated to a high enough level -- around 4,000 degrees Fahrenheit (2,200 degrees C) in the case of a light bulb -- they will emit a good deal of visible light.
How much metal is in my bulb??? • The filament in a light bulb is made of a long, incredibly thin length of tungsten metal. In a typical 60-watt bulb, the tungsten filament is about 6.5 feet (2 meters) long but only one-hundredth of an inch thick. • The tungsten is arranged in a double coil in order to fit it all in a small space. That is, the filament is wound up to make one coil, and then this coil is wound to make a larger coil. • Tungsten is used in nearly all incandescent light bulbs because it is an ideal filament material.
