REVIEW of Static electricity Electricity A. Electric Charge 1. Static electricity is the accumulation of excess electric charges on an object. a. More e¯ = negative charge b. More protons (loss of e) = + charge 2. Charge is conserved (e¯ move from one object to another). None are created or destroyed (if 2 lost only 2 gained)

3. Law of Charges a. Opposite charges attract. b. Like charges repel. 4. Electric fields a. Electric fields exert force on objects within the field. b. Weaker with distance.

5. Transferring electric charge a. Conductors: e¯ move easily. b. Insulators: hold e¯ tightly. c. Contact charging is done when two materials are rubbed together (best with insulators). d. Charging by induction is done when one charged object induces a charge on another.

6. Lightning a. Large static discharge between the earth and clouds. b. Lightning was found to be static electricity by Ben Franklin. 7. Grounding a. Conductive path to Earth. b. Lightning rods & plumbing.

8. The electroscope can be used to detect electric charge

Physics 2015

B. Electric Current 1. The reason electric charge flows from one place to another is voltage. HIGH LOW a. Voltage is the difference in electrical potential between two places where e¯ are flowing. b. Voltage is the “push” that makes electric charges move. c. Measured in volts (V).

2. The flow of electric charge is called current. a. Current is measured in amperes, or amps (A). b. Voltage causes current. 3. The amount of electric charge is measured in coulombs. a. 1 coulomb is the charge carried by 6.24 x 10^18 e¯. b. 1 amp is 1 coulomb per sec.

4. Batteries are e¯ pumps. a. They provide a voltage difference to a circuit. b. Types: wet-cells & dry-cells

5. Resistance a. Opposition to the flow of e¯. b. It changes electrical energy into thermal energy and/or light. c. Measured in ohms. d. Conductors have less resistance than insulators.

e. Wire resistance greater for: 1) Longer wires 2) Thinner wires 3) Higher temperatures

Georg Simon Ohm ( ) -Math/Physics teacher -Known for the Ohm’s law -I = V/R

6. Ohm’s law Voltage Difference Current = Resistance I V R

Electric Circuits  An electric circuit is something that provides a complete path through which electricity travels.  Wires in electric circuits are similar in some ways to pipes and hoses that carry water.

A Basic Circuit All electric circuits have three main parts 1. A source of energy 2. A closed path 3. A device which uses the energy If ANY part of the circuit is open the device will not work!

How you should be thinking about electric circuits: Voltage (V): a force that pushes the current through the circuit (in this picture it would be equivalent to gravity)

Resistance (R): friction that impedes flow of current through the circuit (rocks in the river) How you should be thinking about electric circuits:

Current (I): the actual “substance” that is flowing through the wires of the circuit (electrons!) How you should be thinking about electric circuits: Note: The “I” stands for intensity

Would This Work?

The Central Concept: Closed Circuit

Electrical Symbols Circuit diagrams are a short-cut method of drawing circuits. They don’t need to be perfectly draw, but they can be drawn wrong.

Electrical Symbols WireBattery Paths for electricity to flow.Pushes electricity through circuit.

Electrical Symbols Light Bulb Lights up; resists electricity Resists flow of electricity Resistor

Electrical Symbols What one would look like. Turns electricity on and off. Switch

Simple Circuit When you are drawing a circuit it may be a wise thing to start by drawing the battery first, then follow along the loop (closed) starting with positive and drawing what you see.

Let’s practice drawing the following scenario:  Two light bulbs  One switch  One battery  Wire  series

Simple Circuits  Series circuit All in a row 1 path for electricity 1 light goes out and the circuit is broken  Parallel circuit Many paths for electricity 1 light goes out and the others stay on

Let’s practice drawing the following scenario:  Two light bulbs  One switch  One battery  Wire  Parallel

Series Circuit  In series circuit, the resistors are wired one after another.  Since they are all part of the SAME LOOP they each experience the SAME AMOUNT of current.  See that they all exist BETWEEN the terminals of the battery, meaning they SHARE the potential (voltage).

Series and Parallel Circuits  Series Circuits only one end of each component is connected, one path for current e.g. Christmas tree lights  Parallel Circuits both ends of a component are connected, many paths for current e.g. household lighting

Series Circuit As the current goes through the circuit, the charges must USE ENERGY to get through the resistor. So each individual resistor will get its own individual potential voltage). We call this VOLTAGE DROP. Note: They may use the terms “effective” or “equivalent” to mean TOTAL!

Voltage Drop Each resistor in a series circuit “uses” part of the energy of the circuit, reducing the voltage. Eventually the voltage is back to zero at the negative side of the battery. Then the battery energizes the electrons again.

Current  Electric current is measured in units called amperes, or amps (A) for short.  One amp is a flow of a certain quantity of electricity in one second.  The amount of electric current entering a circuit always equals the amount exiting the circuit.

There are 2 types of Current DC = Direct Current - current flows in one direction Example: Battery AC = Alternating Current- current reverses direction many times per second. This suggests that AC devices turn OFF and ON. Example: Wall outlet (progress energy)

Current  This is moving electrons, moving charge.  Increasing current causes more electricity to move through a device.  Increasing electricity through a device causes it to work faster (in a motor) or be brighter ( in a light bulb) Which bulb would be brighter ?

measuring current Electric current is measured in amps (A) using an ammeter connected in series in the circuit. A

Voltage  Voltage is a measure of electric potential energy, just like height is a measure of gravitational potential energy.  Voltage is measured in volts (V).  A voltage difference of 1 volt means 1 amp of current does 1 joule of work in 1 second.

Voltage  The positive end of a 1.5 volt battery is 1.5 volts higher than the negative end.  If you connect batteries positive-to-negative, each battery adds 1.5 volts to the total.  Three batteries make 4.5 volts.  Each unit of current coming out of the positive end of the three-battery stack has 4.5 joules of energy.

Voltage  Is the electrical potential, how much work the battery can do.  It is linked to energy 1 volt of voltage = 1 joule of energy per coulomb of charge  To increase voltage you could use a stronger battery or add batteries.

Voltage  The light bulb doesn’t light here, because the two batteries are pushing opposite directions. To add together, batteries must be facing the same direction.

measuring voltage The ‘electrical push’ which the cell gives to the current is called the voltage. It is measured in volts (V) on a voltmeter V

Electrical resistance  Resistance measures how difficult it is for current to flow.

Resistance  Slows down current. “Think of resistance like a dam holding back water. “  Adding devices in a circuit increases resistance.  More resistance = less current  Less current = less light

19.3 Measuring resistance  Set the meter to measure resistance (  ).  Set the black and red leads on opposite ends of the objects.

Ohm’s Law I = V/R I = current (amps = A) V = voltage (volts = v) R = Resistance (ohms = Ω)

Calculate time  How much current does a 12 v battery push through a 3 Ω resistor? V = 12 v R = 3 Ω I = ?  12 v / 3Ω = 4A  How strong a battery produces 2 A through a 3 Ω resistor? V = ? R = 3 Ω I = 2 A  2 A X 3 Ω = 6 v

An Example and let’s practice V T = 12 V R T = 6 Ω I T = 2A V 1 = I T R 1 = 2A*1 Ω = 2V V 2 = I T R 2 = 2A*2 Ω = 4V V 3 = I T R 3 = 2A*3 Ω = 6V