Series and Parallel Circuits

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Purpose

To measure current, voltage, and resistance in a simple, series, and parallel circuit.

Taking Data

Part I—Simple Circuit

Connect one resistor (either 5 W or 10 W) to one battery in a simple circuit as shown in class. Sketch the diagram of the circuit at the right. Be sure to connect the ammeter in series with the resistor, and the voltmeter in parallel with the resistor. Collect data on the circuit, and record the highest voltage and current. Using Ohm's law, calculate a value for the resistance. This calculated value for the resistance will be referred to as the measured value since it is determined from two measured quantities, and will be the value placed in the tables. Show your work below.

Q1. Does the measured (calculated) value for the resistance match the value of the resistance printed on the resistor? Note the Value of R in the table is the value calculated using Ohm's Law. Calculate the percent difference between this measured (calculated) resistance (R) and the known (printed) resistance, and show your work below.

Number of batteries	V	I	R
1
2
3
4

Repeat the measurements for 2, 3, and 4 batteries to increase the voltage and current.

Part II—Series Circuit

1. Connect two resistors in series as shown in class. Sketch the diagram of the circuit at the right.

Q2. What should be the total resistance of the two resistors in series?

2. Repeat the voltage and current measurements as in Part I, with the voltmeter across both resistors, and calculate the total resistance using Ohm's law.

Q3. Does the answer to Q2 agree with your measured Value (calculated) for the total resistance in series? Calculate the percent difference between the two.

3. Repeat the measurements for 2, 3, and 4 batteries to increase the voltage and current, filling in the table below.

4. To fill in the last two columns, place the volt meter across each resistor one at a time in this series circuit, and collect data.

Number of batteries	V_tot	I_tot	R_tot	V₁ only	V₂ only
1
2
3
4

Q4. What is the relationship between V₁, V₂, and V_tot?

Part III—Parallel Circuit

6. Connect two resistances in parallel as shown in class. Sketch the diagram of the circuit at the right.

Q5. What should be the total resistance of the two resistors in parallel?

7. Repeat the voltage and current measurements as in Part I, with the voltmeter across both resistors, and calculate the total resistance using Ohm's law.

Q6. Does the answer to Q5 agree with your measured value for the total resistance in parallel? Calculate the percent difference between the two.

8. Repeat the measurements for 2, 3, and 4 batteries to increase the voltage and current, filling in the table below.

9. To fill in the last two columns, place the ammeter in series with each resistor one at a time in this parallel circuit, and collect data.

Number of batteries	V_tot	I_tot	R_tot	I₁ only	I₂ only
1
2
3
4

Q7. What is the relationship between I₁, I₂, and I_tot?

Circuit Lab Questions

1. Why is the ammeter always connected in series with the resistor(s) whose current it is trying to measure?

2. Why is the voltmeter always connected in parallel with the resistor(s) whose voltage it is trying to measure?

3. In general, was Ohm's law verified in this experiment? Explain.

4. Consider the identical light bulbs in the circuit shown.

(a) Which bulb draws the most current, and therefore burns the brightest? Explain.

(b) Explain what will happen to bulbs B and C if bulb A is removed from its socket.

5. A 60 W bulb and a 100 W bulb are connected in series in a circuit.

(a) Which bulb will have the greater voltage across it? Explain.

(b) Which bulb will have the greater voltage across it if they are connected in parallel? Explain.

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