Download Physics 3B Lab 3 Simple Circuits

Physics 42 Lab 6: Simple Circuits
Prelab: Read Chapter 28 and the lab and do all the calculations in it before class for a 3V
power supply and the given resistors. You must have your prelab done to be in class!
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.
The Resistor
Colour Code
Colour Number
Black
0
Brown
1
This resistor has red (2), violet (7), yellow (4 zeros) and gold bands.
So its value is 270000 = 270 k . On circuit diagrams the is usually
omitted and the value is written 270K.
Red
2
Orange
3
Yellow
4
Find the color bands for a 100 Ω Resistor and find the total resistance.
Green
5
Blue
6
Violet
7
Grey
8
White
9
Find the color bands for a 470 Ω Resistor and find the total resistance.
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 390 - 39 = 351 and 390 +
39 = 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 _____________
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?
c) Calculate the expected current drawn by the power supply (total current) and the current
through each resistor (Amps).
I1 = ________________ I2 = __________________ I total = _____________
d) Measure the total current drawn by the power supply and then the current through each
resistor (Amps)
I1 = ________________ I2 = __________________ I total = _____________
Is Ohm’s Law obeyed? By what percent?
2. Parallel Series Circuit
here.
Set up a parallel circuit with two 100Ω resistors. Sketch the circuit
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?
c) Calculate the expected current drawn by the power supply (total current) and the current
through each resistor (Amps).
I1 = ________________ I2 = __________________ I total = _____________
d) Measure the total current and the current through each resistor (Amps)
I1 = ________________ I2 = __________________ I total = _____________
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
through each resistor (Amps).
I1 = ______________ I2 = ______________ I3 = _____________ I total = ____________
b) Measure the total current and the current through each resistor (Amps)
I1 = ______________ I2 = ______________ I3 = _____________ I total = ____________
Is Ohm’s obeyed? By what percent?
c) Calculate the expected voltages across each resistor (volts).
V1 = ________________
V2 = ___________________ V3 = ___________________
d) Measure the voltages across each resistor (volts).
V1 = ________________
V2 = ___________________ V3 = ___________________
Is Ohm’s obeyed? By what percent?
4. You make it up: 2nd 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
through each resistor (Amps).
I1 = ______________ I2 = ______________ I3 = _____________ I4 = __________________
I total = ____________
b) Measure the total current and the current through each resistor (Amps)
I1 = ______________ I2 = ______________ I3 = _____________ I4 = __________________
I total = ____________
Is Ohm’s obeyed? By what percent?
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 = ______________
Is Ohm’s obeyed? By what percent?
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.