Lab 2A Worksheet - Lab assignment from the online course PDF

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Lab assignment from the online course ...

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Group #:________________ People (please print names) 1. 2. 3.

Lab 2A: DC Circuits - Measurements of Voltage, Resistance and Current 1. Unpack your digital multimeter, supplied wires with alligator clips, and the 9-V battery you bought. Figure out how to set the meter to measure the voltage V of the battery. (No, it’s not a trick question. The answer probably won’t be exactly 9.000 V.) Use the supplied wires to make a stable circuit so that you can repeat the voltage measurement about 5 to 10 times. Do you get a consistent value? How much variation in the voltage do you find? Write your result as Voltage = V ± ΔV. (For example, your results might be Voltage = 6.35 ± 0.02 V. However, if you got this value, you would need to buy a new battery before you start your lab.) Using your phone take a picture of your circuit. Each group member should make their own measurements then you need to put together your results and fill in the following table: Name V ± ΔV results 1 9.35 ± 0.01 2

9.54 +- .01 V

3

9.47 ± 0.01 V

4

9.66+-0.01V

5 2. Decide within your group which picture of this first circuit is the best, and insert it here. Make sure that the multimeter is visible in the picture so that the Instructor can see the setting on it.

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3. Figure out how to set the meter to measure the resistance R of the provided resistor. Hint: This resistance will be close to, but not exactly, 10kΩ = 10,000Ω. Use your supplied wires to make a stable circuit as before. It is very hard for a person to keep meter probes in good contact with the surfaces of a battery or resistor. Let the alligator clips make your work easier. If your measured values are “jumping around” it probably means you have loose contacts somewhere. Make several resistance measurements and write your result as Resistance = R ± ΔR. Each group member should make their own measurements then put together your results and fill in the following table: Name R ± ΔR results 1 9.67 ± 0.01 2

9.75 +- 0.01

3

9.51 ± 0.01

4

10.07 + -0.01

5

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4. Draw a series circuit consisting of your battery and resistor. Using the values you measured above and Ohm’s Law, it should be possible to calculate the value of the current I which flows in this (so-far imaginary) circuit. Calculate your best estimate of the Current I= I ± Δ I.

Hint: If you knew V and R exactly, you could find an exact value of I = V/R. In your experiments, both V and R may have uncertainty! To find the smallest I, you could calculate (V-ΔV)/(R+ΔR). That is, the smallest numerator that you measured divided by the largest denominator you measured. Make sure this makes process makes sense to you. How would you find the largest I predicted by your measurements of V and R? 5. Using your multimeter, battery, resistor and connecting wires, construct the series circuit described above. Figure out how to set the meter to measure the current I in the series circuit. How must the meter be attached to the circuit? Hint: the technique for measuring current is different than measuring voltage drop and resistance; you must connect the meter in series with the resistor and the battery. If not connected correctly the multimeter may stop working and in that case you will need to purchase a new fuse. Make several measurements and confirm that the observed variations are small. “Open” the circuit between measurements so that the battery doesn’t run down during your experiment. Write down your results as Current = I ± Δ I. Compare your measured results for current with the calculated results from question 4 above. Considering the levels of uncertainty in the values, are the calculated and measured currents the same or different? Explain your results briefly.

Each group member should make their own calculations and their own measurements then put together your results and fill in the following table:

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Name 1

I ± ΔI calculated .967 ± 0.01

I ± Δ I measured 0.91 ± 0.01

2

0.978 +- 0.002

0.95 +- 0.00

3

0.99 ± 0.01

0.951 ± 0.01

4

0.89 + -0.002

0.96 + -0.00

5 Decide within your group which picture of this circuit is the best, and insert it here. Again, make sure that the multimeter is visible in the picture so that the Instructor can see the setting on it.

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