Unit 10 Electricity and Magnetism

1. Unit 10Electricity and Magnetism Reference: Ch 20-26

2. Circuit Diagrams What is Electricity? • Circuits: made up of wires and parts such as batteries, light bulbs, motors, or switches. • When diagramming circuits, use symbols to represent parts of the circuit. The flow of electric current in wires, motors, light bulbs, and other devices. Electric current carries energy over great distances.

3. Common Electrical Symbols Straight lines represent wires. Switch Battery Light Bulb Resistor NOTE: In many circuit diagrams, any electrical device is shown as a resistor. A resistor is an electrical component that uses energy. Sometimes when showing how a circuit works, light bulbs might be treated like resistors.

4. Open vs Closed Circuits Electricity cannot travel through an open circuit: path is broken. Electricity can travel easily through a closed circuit: there is a complete path. A short circuit is usually an accidental extra path for current to flow.

5. Electric Charge Like charges repel Opposite charges attract Electroscope Is the source of shocks and sparks Electrically charged: If materials or objects carry excess + or – charge Most matter is neutral (no charge) An electroscope can detect charged objects. The leaves attract or repel each other depending on the charge nearby

6. Batteries and Voltage Batteries • Use chemical energy to move charges • Amount of potential energy = voltage • Battery like a water tower: water flows from high energy (top of tower) to low energy • Circuit transfers energy from battery to object Voltage • Electric charge flows from high energy (voltage) to lower energy. • Voltage is measured using a voltmeter • All points on a wire are the same voltage. • Voltage is reduced when energy is used. • Supplies energy to make charges flow.

7. Current • Flow of electric charges • Does work • Measure current using an ammeter • Circuit breakers or fuses stop too much current from flowing. • Types of current: • Alternating (AC): direction of current goes back and forth • Example: household current is AC • Direct (DC): current flows in one direction. • Example: battery

8. Electrical Conductivity • Property of a substance: its ability for current to pass through • Conductors- electrons come free and can move to create electrical current • allow current to pass • metals • Insulators- electrons are tightly bound to atoms and cannot move • block current • Usually nonmetals, some plastics, foam or rubber • Semiconductors- in between in ability to conduct current • Computer chips, LED’s, some lasers

9. Resistance • Measures how easily charges flow through • Compare to pouring water out of jar: if opening is small  lots of resistance; if opening is large  water flows quickly b/c of less resistance • Ex: The more light bulbs strung together the higher the resistance. (decreasing the current) Factors affecting resistance • Thickness • Thick wire has a lower resistance and can safely carry more current than thin wire • Length • The longer the wire, the more resistance it has

10. Ohm’s Law • The relationship between amps, volts and ohms • Current • Unit: Amps • Symbol: I • Voltage • Unit: Volts • Symbol: V • Resistance • Unit: Ohms • Symbol: R

11. Series vs Parallel Circuits Series Circuits • Current can only take one path • If multiple bulbs in circuit, if one goes out they all go out • Series circuits would not work in the home because all electrical items would have to be on all the time to keep the circuit closed Parallel Circuits • Current can take more than one path • If multiple bulbs are in circuit, if one goes out, the others will still light • Homes are wired with parallel circuits