Physics 42 Lab 6: Simple Circuits

Transcription

1 Print Name: Lab Physics 42 Lab 6: Simple Circuits Equipment: (2) 100 Ω resistors, (2) 470Ω resistor, KRM Multimeters, Circuit Board Kits, HP Power Supply, black and red banana cables Part 1. Resistor values - the resistor colour code Most resistors have 4 bands: The first band gives the first digit. The second band gives the second digit. The third band indicates the number of zeros. The fourth band is used to shows the tolerance (precision) of the resistor. This resistor has red (2), violet (7), yellow (4 zeros) and gold bands. So its value is = 270 k. On circuit diagrams the is usually omitted and the value is written 270K. Find the color bands for a 100 Ω Resistor and find the total resistance. Find the color bands for a 470 Ω Resistor and find the total resistance. The Resistor Colour Code Colour Number Black 0 Brown 1 Red 2 Orange 3 Yellow 4 Green 5 Blue 6 Violet 7 Grey 8 White 9 Tolerance of resistors (fourth band of colour code) The tolerance of a resistor is shown by the fourth band of the colour code. Tolerance is the precision of the resistor and it is given as a percentage. For example a 390 resistor with a tolerance of ±10% will have a value within 10% of 390, between = 351 and = 429 (39 is 10% of 390). A special colour code is used for the fourth band tolerance: silver ±10%, gold ±5%, red ±2%, brown ±1%. If no fourth band is shown the tolerance is ±20%. In lab, find the tolerances of your resistors and put them here: Tolerance for 100 Ω Tolerance for 470 Ω

2 Part 2: Experiment with Resistors in Parallel and Series (The Voltage is 3V for all circuits!) Voltmeter settings: Direct Current ( V -----), 20. This setting will give you Volt readings. Ammeter Settings: To measure current set dial to Direct Current, ( A ----) 200m, Black cable into COM, Red cable into Fused ma. This will give you milliamp readings. NEVER MEASURE CURRENT WITHOUT A LOAD! If you measure current straight out of the power supply you will fry out little multimeter!!! (You FRY you BUY! ;-) 1. Series Circuit Set up a simple circuit with two 100Ω resistors in series. Connect voltmeter to the dc voltage supply. Turn Voltage adjust to zero (ccw) before turning on. Turn on the power supply and slowly turn up voltage till you read 3 V on the voltmeter. This might take some fine tuning and patience. Once it is set, leave it alone for the rest of the lab! If you happen to change it, you can always set it again with your voltmeter. Sketch the circuit here. Power Supply Voltage: V = a) Calculate the equivalent resistance of the circuit: Calculate the expected voltages across each resistor and then across both (volts). V1 = V2 = V1 + V2 = b) Measure the voltages across each resistor and then across both (volts). V1 = V2 = V1 + V2 = Is Ohm s Law obeyed? By what percent? Show calculations. Box answers. c) Calculate the expected current drawn by the power supply (total current) and the current

3 d) Measure the total current drawn by the power supply and then the current through each resistor (Amps) Is Ohm s Law obeyed? By what percent? Show calculations. Box answers. 2. Parallel Series Circuit Set up a parallel circuit with two 100Ω resistors. Sketch the circuit here. a) Calculate the total equivalent resistance of the circuit: Calculate the expected voltages across each resistor and then across both (volts). V1 = V2 = b) Measure the voltages across each resistor (volts). V1 = V2 = Is Ohm s Law obeyed? By what percent? Show calculations. Box answers. c) Calculate the expected current drawn by the power supply (total current) and the current

4 d) Measure the total current and the current through each resistor (Amps) Is Ohm s Law? By what percent? 3. Complex Circuit Set up parallel circuit with two 100Ω (R1, R2) resistors in parallel with each other and in series with a 470Ω resistor (R3). Draw the circuit here: a) Calculate the equivalent resistance of the circuit: Show your calculation here: Calculate the expected current (Amps) drawn by the power supply (total current) and the current I1 = I2 = I3 = I total = b) Measure the total current and the current through each resistor (Amps) I1 = I2 = I3 = I total =

5 c) Calculate the expected voltages across each resistor (volts). V1 = V2 = V3 = d) Measure the voltages across each resistor (volts). V1 = V2 = V3 = 4. You make it up: 2 nd Complex Circuit with 4 Resistors: Design and set up a circuit with two 100Ω (R1, R2) resistors with two 470Ω resistor (R3 & R4). Mix it up have it part parallel and part series!! Draw the circuit here: a) Calculate the equivalent resistance of the circuit: Show your calculation here: Calculate the expected current (Amps) drawn by the power supply (total current) and the current I1 = I2 = I3 = I4 = I total = b) Measure the total current and the current through each resistor (Amps) I1 = I2 = I3 = I4 = I total =

6 c) Calculate the expected voltages across each resistor (volts). V1 = V2 = V3 = V4 = d) Measure the voltages across each resistor (volts). V1 = V2 = V3 = V4 = 5. Summarize your results. Was Ohm s Law obeyed within the tolerance of your resistors for each circuit? Average the voltage and current uncertainty for each circuit. Briefly discuss your results.