If you are given a light bulb A

If you are given a light bulb, A) What other equipment would you need to light it up? B) How would you set up the equipment? http: //phet. colorado. edu/en/simulation/circuit-construction-kit-dc

• Battery acts as the pump to push the charges (electrons) around the circuit http: //phet. colorado. edu/en/simulation/circuit-construction-kit-dc

B. Current (definition): HOW QUICKLY CHARGE MOVES • Equation (see ref. tabs. ) I = Δq t • Units: I = Current Δq = change in charge t = time C/s = Ampere (A)

Note: High currents through your body can cause serious injury or death. Here a few of the typical consequences of different currents “It’s the volts what jolts, but it’s the mills that kills. ”

CHANGE IN POTENTIAL between • What is needed? A ______ 2 ______ points in the circuit Provided by: Battery or chemical cell Most types of 9 V batteries consists of 6 1. 5 V cells added in series

A. Potential Difference (V): Change in electric potential energy between two positions • PROVIDES THE ELECTRICAL “PUSH” • Units: Volts (V) B. Resistance: OPPOSES THE FLOW OF CHARGES • Units: Ohm (Ω)

C. Ohm’s Law (see ref. tabs. ) R=V I R = Resistance (Ω) V = Potential Difference (V) I = Current (A)

• Device used: AMMETER • How to set it up: Place in series (line) with circuit

• Device used: Voltmeter • How to set it up: Place it across the device you want to measure

• Resistivity - A characteristic of a material that depends on its electronic structure and temperature • Factors that affect the resistance: ↑ R) LENGTH 1. _____ (Increase __ L => ____ ↓ R) THICKNESS/AREA A => ____ 2. __________ (Increase ____ http: //phet. colorado. edu/en/simulation/resistance-in-a-wire

• Factors that affect the resistance: ↑ R) ρ MATERIAL/RESISTIVITY (Increase _____ 3. ___________ => ____ SEE REFERENCE TABLES FOR VARIOUS RESISTIVITIES – pg. 4

• Factors that affect the resistance: ↑ R) 4. _______ T => ___ TEMPERATURE of wire (Increase ____

• Equation (see ref. tabs) ↑

Example: Determine the resistance of a copper wire that has a cross-sectional area of 2 x 10 -3 m 2 and 40 m long.

• Mechanics’ Equation for Power: P=W Units: J/s = Watt (W) t • Electric Power: P = W = IV t • Alternate Equations (see ref. tabs. ): P = IV = I 2 R = V 2 R

Example: A microwave draws 12. 5 amperes of current and resistance of 9. 6 ohms. What is the power dissipated in the resistor?

Example: A 60 W and 100 W light bulb are plugged into the wall that provides a potential difference of 120 V. Which bulb has the greater resistance? What is the resistance of both?

• Equations: W = Pt = IVt = I 2 Rt = V 2 t R Units: Joule (J)

Example: A television set draws 2 A when operated on 120 V. A. How much power does the set use? B. Calculate how much energy is used if the television is on for 2 hours a day.

• All parts are connected to provide a SINGLE PATH for the current _______ • Schematic Diagram: Draw a circuit diagram with three resistors set up in series hooked up to a 12 V battery. http: //phet. colorado. edu/en/simulation/circuit-construction-kit-dc

• Things to Remember (See Ref. Tabs) 1. Current: Remains constant through each resistor Equation: I = I 1 = I 2 = I 3 = … 2. Equivalent Resistance: Total resistance is equal to the SUM of all resistors Equation: Req = R 1 + R 2 + R 3 + … 3. Voltage Drops: Applied (total) voltage from the power source equals the sum of the voltages across each device (resistor) Equation: V = V 1 + V 2 + V 3 + …

Example: Draw a circuit diagram for series circuit that contains a 5 ohm, 10 ohm, and 15 ohm resistor that are connected to a 20 V battery. Include an ammeter to read the total current and three voltmeters to measure the potential difference across each resistor. Resistor 1 2 i. Calculate the total resistance of the circuit. i. Calculate the total current in the circuit. i. Calculate the potential difference across each resistor. 3 Total V I R P

TWO OR MORE PATHS for the current • Allows __________ to flow • Schematic Diagram: Draw a circuit diagram with three resistors set up in parallel connected to a 12 V battery.

• Things to Remember (See Ref. Tabs) 1. Current: Sum of the currents in each of the branches is equal to total current Equation: I = I 1 + I 2 + I 3 + … 2. Voltage: Voltage remains constant across each device Equation: V = V 1 = V 2 = V 3 = … 3. Equivalent Resistance: As more resistors are added in parallel, total resistance DECREASES 1 1 Equation: = + + + … Req R 1 R 2 R 3

Example: Draw a circuit diagram for parallel circuit that contains a 10 ohm, 15 ohm, and 20 ohm resistor that are connected to a 20 V battery. Include ammeters to measure the current through each and voltmeters to measure the potential difference across each resistor.

i. Calculate the equivalent resistance of the circuit. Res. 1 2 ii. What is the potential difference across each resistor? 3 Total iii. Calculate the reading on each of the ammeters. iv. Calculate the total current (the current leaving the source). v. What would happen to the total current if more resistors are added in parallel? V I R P

• Like energy, there is a conservation of CHARGE in circuits _____ • Junction Rule: SUM of the currents entering a junction _______ SUM of the currents EQUAL the _______ must ____ leaving

• What is the reading on each of the ammeters and direction of current? (if not given)

• DC (Direct Current) (video clip/animation) - current (charges) flows in the same direction between the + and - terminals - used in many electronic devices (ie – computers) - can be produced by batteries, solar cells, fuel cells • AC (Alternating Current) - the direction of the current (charges) reverses (alternates) - in the US it does this at a rate of 60/sec or 60 Hz - advantage is that power companies save a lot of money transmitting power at very high voltages over long distances - they convert AC to high voltages for transmission (above 100, 000 V) then use transformers to step down to lower volts

Great Minds – Nikola Tesla (10 min) Thomas Edison (DC – Low Voltage) vs. Nikola Tesla (AC – High Voltage) Video (6 min) The high current problem P = IR 2

Sending AC Electricity (How does electricity get to you? ) Probably the biggest advantage of AC is that you can use high voltages with small currents to reduce losses when you transmit power. Remember that lost energy increases the more collisions you have, and reducing current decreases the amount of collisions (and reduces heating in the wires). You can send power with DC, but the DC power transmission loses a lot of energy. You would have to put much more effort into sending DC power over the same distance