U3e-L3 February 25, 2010 DRILL Why are the + and – symbols unnecessary when drawing the power source in an electric schematic? A ______ circuit occurs when the positive terminal is connected directly to the negative terminal by a conductor, with no resistance. Short 1. The length of the lines tell you which is positive and which is negative

Which of the following is a schematic? U3e-L3 Electric Schematics What is a schematic? Which of the following is a schematic? A schematic is a diagram that represents the elements of a system without using realistic pictures

Complete problem #5 on your worksheet U3e-L3 Problems – Joule’s Law Complete problem #5 on your worksheet

U3e-L3 Problems – Joule’s Law A Honda Insight (hybrid) has a 144 Volt battery system in its trunk. The electric motor that the batteries power can generate 20,000 Watts of power. Sketch a schematic diagram of this circuit. What is the current traveling through this high voltage circuit? Write the given information: V = 144 volts P = 20,000 watts I = ? A schematic is a diagram that represents the elements of a system without using realistic pictures

Problem #5 – Joule’s Law Write the given information: V = 144 Volts U3e-L3 Problem #5 – Joule’s Law Write the given information: V = 144 Volts P = 20,000 Watts I = ? Sketch a schematic diagram of the circuit: Start with power source Add conductors Add load Add current + P = 20,000 W V = 144V - I = ?

Problem #5 – Joule’s Law Write the given information: V = 144 Volts U3e-L3 Problem #5 – Joule’s Law Write the given information: V = 144 Volts P = 20,000 Watts I = ? Rearrange, Substitute, and Solve Sketch a schematic diagram of the circuit: R = ? 5V .7A P = V x I I = 20,000W / 144V R = 138.9 A I = P / V

Homework Problems #2 and 3 Review U3e-L3 Problems – Joule’s Law Homework Problems #2 and 3 Review

Homework Problem #2 Write the given information: V = 9 Volts U3e-L3 Homework Problem #2 Write the given information: V = 9 Volts I = .02 Amps R = ? Rearrange, Substitute, and Solve Sketch a schematic diagram of the circuit: R = ? 9V .02A V = I x R R = 9V / .02A R = 450 W R = V / I

U3e-L3 Homework Problem #3 Write the given information: V = 120 Volts I = 5 Amps R = ? Rearrange, Substitute, and Solve Sketch a schematic diagram of the circuit: R = ? 120V 5A V = I x R R = 120V / 5A R = 20 W R = V / I This is how alternating current (AC) power sources are represented schematically

Direct Current The unidirectional flow of electrons. U3e-L1 Direct Current The unidirectional flow of electrons. Direct current is current travelling in 1 direction – from the negative terminal to the positive terminal. Direct current is used in almost all electronic systems as the power supply. Batteries are a sign of direct current. one I

Direct Current Measuring the voltage of a direct current power supply: U3e-L3 Direct Current Measuring the voltage of a direct current power supply: The voltage is constant. 1.5 V

U3e-L3 Direct Current If voltage is constantly 1.5 V, what does its graph over time look like? 1.5 V Voltage (volts) 1 2 3 0 2 4 6 8 10 12 14 Time (seconds)

U3e-L3 Alternating Current Electrons flow back and forth through an electric circuit. Most artifacts you plug in. R = ? 120V 120 V + -

U3e-L3 Alternating Current If voltage is alternating 120 V to -120 V, what does its graph over time look like? +/-120 V Voltage (volts) -120 0 120 0 2 4 6 8 10 12 14 Time (seconds)

Resistance Calculations U3e-L3 Resistance Calculations Resistors in series are added: R1 R2 R3 Total Resistance: R = R1 + R2 + R3 T

Resistance Calculations U3e-L3 Resistance Calculations Resistors in parallel: add their reciprocals R1 R2 R3 Total Resistance: 1 1 1 1 = R R1 + R2 + R3 T

Resistance Calculations U3e-L3 Resistance Calculations Calculate the resistance in the following circuit: 100 W 100 W 100 W Total Resistance: R = R1 + R2 + R3 T R = 100 W + 100 W + 100 W T R = 300 W T

Resistance Calculations U3e-L3 Resistance Calculations Calculate the resistance in the following circuit: 100 W 100 W 100 W Total Resistance: 1 1 1 1 = R R1 + R2 + R3 T

Resistance Calculations U3e-L3 Resistance Calculations 1 1 1 1 1 1 1 = = + + R R1 + R2 + R3 100 100 100 T 1 .01 + .01 + .01 = R T 1 = .03 (Multiply both sides by Rt) R T 1 = .03 x Rt .03 .03 Rt = 33.3 W

Solve for V, I, R, and P for each of the six problems. U3e-L3 CLASSWORK/HOMEWORK Complete the worksheet on electrical problems using Joule’s and Ohm’s Laws. Solve for V, I, R, and P for each of the six problems.