Electricity & Magnetism

Transcription

1 Electricity & Magnetism Unit 7 Recall that Atoms l Have neutrons, protons, and electrons. l Protons are positively charged l Electrons are negatively charged l Opposite charges attract l Same charges repel 1

2 Electrons l Are located on the outer edges of atoms they can be moved. l A concentration of electrons in an atom creates a net negative charge. l If electrons are stripped away, the atom becomes positively charged. The world is filled with electrical charges:

3 l Balloon phet Balloon Demo Potential electrical energy is called: l Static Electricity

4 Static Electricity l The build up of an electric charge on the surface of an object. l The charge builds up but does not flow. l Static electricity is potential energy. It does not move. It is stored. 3 Ways for Static Electrcity to Build Up l Friction - rubbing l Conduction direct contact l Induction through an electrical field (not direct contact) l phet Balloon Demo 4

5 Static Discharge l Occurs when the potential energy of static electricity moves and evens out the charges/balances the charges again PHET John Travoltage l link to Demo 5

6 Moving/Kinetic Electrical Energy is Current Electricity l Current: The flow of electrons from one place to another. l Flows through wires l Measured in amperes (amps) How can we control currents? l With circuits. l Circuit: is a path for the flow of electrons. We use wires. 6

7 There are 2 types of currents: l Direct Current (DC) Where electrons flow in the same direction in a wire. l Batteries are DC l (chemical energy) There are 2 types of currents: l Alternating Current (AC) electrons flow in different directions in a wire l Due to changing poles of a magnet spinning by wire l Negative poles cause the negative electrons to be repelled l Wall outlets are AC l generator 7

8 There are 2 types of circuits that DC and AC electricity can use: l Circuit = the path the electricty flows l Series Circuit: the components are lined up along one path. If the circuit is broken, all components turn off. Series Circuit 8

9 There are 2 types of circuits: l Parallel Circuit there are several branching paths to the components. If the circuit is broken at any one branch, only the components on that branch will turn off. Parallel Circuit 9

10 Materials can be either conductors or insulators l Conductors material through which electric current flows easily. l Insulators materials through which electric current cannot move. Examples l Conductors: l Metal l Water l Insulators: l Styrofoam l Rubber l Plastic l Paper 10

11 What is Resistance? l Electrical friction l The opposition to the flow of an electric current, producing heat. l Measured in ohms. l Abbreviated as R l Good conductors have low resistance. What is Voltage? l The measure of the force of energy given to the charge flowing in a circuit. l The greater the voltage, the greater the force or pressure that drives the charge through the circuit. l Measured in volts l Abbreviated as V 11

12 What is Current? l The rate that the electricity flows l Measured in amperes (Amps) l Abbreviated as I Ohm s Law the relationship between voltage, resistance and current Voltage (V)= current(i) X resistance(r ) l the force = the flow of electricity X the resistance l V = I x R 12

13 How is electricity produced? l Generator a machine that changes mechanical energy to electrical energy phet link l Usually use moving magnets to create currents in coils of wire. l Electrical energy video How electricity creates light l Thin wire in the bulb creates lots of resistance ( friction) = heat l Heat energy converts to light energy l How light bulb works 13

14 Related Activities l phet lab on Ohm s Laws l Ohm s Laws Calculation Worksheet l Electricity video and worksheet l Build series and parallel Circuits 14