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Electricity PowerPoint Presentation General Science

The document explains electricity as a form of energy composed of charges that can produce light, heat, or motion, detailing its types: static and current electricity. It describes the behavior of electric charges, the role of conductors and insulators, and the principles governing electric circuits and their components. Additionally, it discusses the generation of lightning and the effects of electric currents and charges in various materials.

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Electricity
What Is Electricity? • A form of energy made up of charges that can produce light, heat, or motion
Kinds of Electricity Static • An electric charge that collects or builds up on the surface of an object • Examples – Shocking – Lightening Current • The flow of electric charges carried through a material such as wire or other conductors • Examples – Power lines – Computers – Appliances
Conductors and Insulators Conductors • Any material that allows electric charges to move through it • Examples: – Metals (esp. copper) – Your body – Electric wires Insulators • Materials that do not allow electric charges to flow freely through them • Examples: – Wood – Glass – Rubber
Static Electricity • Losing electrons means that the atom has more protons than electrons, which cause it to carry a net positive charge. • Because electrons can move along atoms, they can build up in matter, a phenomenon known as Static Electricity • Inside every substance, there are millions of tiny electrical charges. • All matter contains atoms (electrons are negative, protons are positive, and neutrons are neutral).
Static Electricity • Protons and electrons are usually equal and this makes the substance electrically neutral. • This balance can be upset, however, by rubbing. Let us assume that both the dry cloth and the polythene rod have neutral charge before the experiment. This means that the amount of protons in the nucleus is the same as the amount of electrons orbiting around the nucleus. If you rub a polythene rod with a woolen cloth, electrons are transferred from wool towards the surface of the polythene rod. The woolen cloth now has more positive charges than negative charges and so it becomes positively charged while the polythene rod becomes negatively charged. Rubbing gives the polythene rod static electricity. Static means not moving.
Build Up of Electric Charges • Glass, wood, plastic, and many other substances can become charged by rubbing. • Charged objects affect each other when they are brought close together. • They either pull on, or attract each other – or they push away, or repel each other.
Build Up of Electric Charges • When electrical charges collect on the surface of an object and tend to remain there, they are called static charges. • An object acquires static electricity as a result of friction between itself and another object. When a plastic comb is rubbed against a woolen cloth, the comb will attract many kinds of light objects, such as bits of paper.
Lightning • Movement of thunder clouds in the sky generates lightning. An electric discharge that occurs between a positively charged area and a negatively charged area Can occur: 1. Cloud to cloud 2. Cloud to earth 3. In the same cloud • https://www.youtube.com/watch?v=EM_sN_ YHNow
Thunder • The sound that results from rapid movement of air along a lightning strike • As lightning flashes through the sky, it causes the air to expand suddenly. With this sudden expansion comes the loud rumble we call thunder • Occurs during Thunderstorms • Lightning first – then thunder because light travels faster than sound.
Lightning • kills more than 60 people • injures more than 400 people a year in the US • one mile every five seconds • about 50,000 F
Limit Exposure
Current Electricity
Current Electricity – what have we discussed: static electricity • Properties of Conductors & Insulators. • Transfer of charge through various methods. • Difference between static and current electricity. • Formulas.
We’ll apply what we know to current electricity. What does current mean? What does electric current mean? Flow or motion. Flow or motion of electric charge.
What will happen if two oppositely charged metal plates touch? Until the plates have equal charge. How long? Hint: Remember The conducting spheres.
We can use Energy of charges in motion to do work. If we transfer charges from high PE to low PE, the charge can do some work converting Energy – but not for long.
With static I can charge an object, & transfer the electric charge to do work. Static electricity is quick transfer of charge but charge stops when equilibrium reached. We often want continuous flow of charge because we want continuous work.
Current still needs a potential difference/voltage to push charges to move. The pd/voltage gives a push.
Current Electricity requires constant source of potential difference or voltage. • Battery • Wall outlet • Generator • Solar Cell
Constant Potential Dif/Voltage induces charges to move continuously.
Voltage/p.d. provides the “push” or “pressure” to charges. Think of 1 side as more + and 1 side as more negative The higher the voltage/p.d., the more push or pressure each charge gets, the more energy each charge has, the more mechanical work each charge can do. + -
Outlet has p.d. = 120V. Don’t stick a fork in it!!
An electric circuit allows current to flow and to do continuous work. Circuits need the following components: • A source of continuous voltage. • A closed pathway, circuit of conductors for charges to flow. • Resistor to convert electric enery to some other form (heat, light, sound etc.)
Solids only e- flow. Liquids any charged particles or ions can flow. Which type of charges can move?
Circuits
Circuit – Closed pathway for charges. All components need p.d. to move. Potential Dif/ Voltage Gives the push Conducting path (wire). Easy to move current through very little p.d. needed. Resistors – (bulbs) Difficult for current to flow. Larger p.d. needed.
Work & Energy on Charges (q) in circuit. Battery does work on q. Q pushed into Conducting path (wire). Resistors – (bulbs) PEchm – PEelc Q in motion. PEelc - KE Work on q, PEelc &KE – heat, light. PEelc used up, PEchm, starts cycle again.
Bulbs, toasters, computers... convert KE of e- to other forms of E – heat, light etc. Devices are called resistors or loads. They slow down the e- so they resist current flow. (Like paddle wheel in river). A Closer Look at Resistors
As e- flow through filament, KE lost to heat & light. What must be around the bulb to push e- through it? p. d.
R = V/I V = volts J/C I = current A, C/s R = resistance ohm’s  or V/A. Resistance (R) unit = ohm’s . Ohm’s Law Relates Resistance, Current, Voltage
Resistance in Wires Occurs in wires as well as appliances. Certain factors affect how much resistance a wire will offer to current flow.
Factors affecting wire resistance. 1. Length 2. Area 3. Temperature 4. Type of material
Length – longer wire offers more resistance. More chances for friction in wire. More resistance Less resistance
Cross Sectional Area Thick wires offer less resistance.
Temperature Hot offers more R Cold offers less R
Work done Since Power is Work/Time, Power x Time = Work or Energy
Fuses As current flows, wires heat up. Fuses designed to break circuit if current becomes to high for the wires. Fuse should be rated just above the ideal operating current for a circuit.
Kilowatt hours kWh. • Power is a rate of energy use. • Electric sold in kWh which is Pt. • 1 kWh is energy delivered to home in 1hour. • 1 kWh (1000 W/kW)(60 min/h)(60s/min) = 3.6 x 106 Ws = 3.6 x 106 J
Circuit Symbols
Electricity Know what it is Know the different kinds Know about the different kinds of circuits Know about conductors and insulators
The End