Chapter 20

I. Electric Charge Electric charge – an electric property of matter that creates a force between objects

1. opposites attract 2. like charges repel 3. conductors allow charge flow (insulators do not)

3. Conductors allow charges flow (insulators do not) Ex. Appliance Cords 4. Objects can be charged by the transfer of electrons Ex. You slide across the fabric car seat some electrons can be transferred form on material to another (charged by friction)

II. Electric Force Force of attraction or repulsion between objects due to charge 1. Electric force depends on charge and distance 2. Electric force acts through a field Electric field – the region around a charged object in which other charged objects experience

Like charges field lines

Opposite charges

D. Static Electricity and Charging Charge can be transferred by friction, by contact, and by induction Law of conservation of charge : The total charge in an isolated system is constant

1. Charging by friction

2. Charge by contact

3. Charge by induction

Current I. Voltage and Current Electrical potential energy – potential energy of a charged object due to its position in an electric field 1. Potential Difference is measured in volts (often called voltage)

2. There is voltage across the terminals of a battery

3. Cell Device that is a source of electric current They convert chemical energy to electrical energy They contain electrolytes( conduct electricity) They contain 2 electrodes with different conducting materials

4. Voltage Sets charges in motion Current – rate that electric charges move through a conductor SI unit for current = Ampere (Amp)

II. Electrical Resistance Light bulbs 40W or 100W shine differently because of the amounts of current

1. Different current is due to their resistance Resistance- ratio of the voltage across a conductor to the current it carries R = V/ I or Resistance = voltage/current SI units Resistance= ohm (Ω) Voltage = Volts (V) Current = Amperes ( amp)

Example 1. R=V/I What resistance would produce a current of 150 ampere with a potential difference of 5000 volts? R = 5000/50 R = 33.3Ω

Example 2 R=V/I A 12 volt battery produces a current of 30 amperes. What is the resistance? R = 12/30 R = 0.04Ω

Example 3 R=V/I Find the current when a 12-volt battery is connected through a resistance of 36 ohms. I = V/R I = 12/36 I= .333 amps

3. Conductors have low resistance 4. Some materials become superconductors below a certain temperature. Critical temperature- falls below a -272°C and -123°C Superconductor : niobium, tin, mercury, oxygen

5. Insulators have high resistance Grounding is an important part of electrical safety. (provide a pathway for the current to leave the charged object) 6. Semiconductors- in pure state they are insulators

I. Circuits Electric circuit- device connected so that it provides one or more complete paths for movement

II. Series Circuits Series- describes a circuit or portion of circuit that provides a single conducting path

III. Parallel Circuit Describes components in a circuit that are connected across common points providing two or more separate conducting paths

Identify the following as series or parallel

IV. Electric Power and Electric Energy 1. Power = Current x Voltage Or P = IV SI UNITS: Power = Watts Current = amperes Voltage = Volts

Example 1. P = IV A 6- volt battery produces a current of 0.05 amps. What is the power in the circuit? P = 6 x 0.05 P = 0.3

V. Fuses and Circuits Breakers 2. Electric companies measure energy consumed in kilowatts and hours 1kW x hour = 3.6 x 106 J V. Fuses and Circuits Breakers Two or more wires touch = short circuit

V. Fuses and Circuits Breakers Two or more wires touch = short circuit 1. Fuses – an electrical device containing a metal strip that melts when current becomes too great

2. Circuit Breaker Device that protects a circuit from current overloads

IV. Electric devices A. Electronics convey information with electrical patterns called analog and digital 1. Analog signals – smooth varying signal produced by continuously changing the voltage or current in a circuit 2. digital signals – encodes information as a string of 1’s and 0’s. Works like Morse code. Digital is more reliable than analog