SERIES AND PARALLEL RESISTORS



SERIES AND PARALLEL RESISTORS

Procedure:

1. Alternately connect 1 (trial #1), 2 (trial #2), and then 3 (trial #3) small light bulbs in a series arrangement with the lab table power supply. Each row n the data table represents a single trial.

2. For each trial, use a voltmeter to measure the potential difference across each lamp and the total potential drop across the whole series. Also, use an ammeter to measure the current flowing through each lamp.

3. Draw circuit diagrams for each trial.

4. Important: Keep the same bulb as same numbered bulb in each trial. You may want to label the light bulbs in order to keep track of them.

Data Table: Resistors in Series

| | | | | | | | | | | |Calculated Resistance |Calculated Power | |Trial |Total |Bulb #1 |Bulb #2 |Bulb #3 |Total |Bulb #1 |Bulb #2 |Bulb #3 |Total |Bulb #1 |Bulb #2 |Bulb #3 | | |VT(V) |IT(A) |V1(V) |I1(A) |Bright |V2(V) |I2(A) |Bright |V3(V) |I3(A) |Bright |RT(() |R1(() |R2(() |R3(() |PT(W) |P1(W) |P2(W) |P3(W) | |1 Bulb | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |2

Bulbs | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |3

Bulbs | | | | | | | | | | | | | | | | | | | | |

Sample Calculations for Trial #3:

5. Alternately connect the same three light bulbs in a parallel arrangement across the lab table power supply until all three are connected in parallel. Be sure to keep the same numbered bulbs as the previous trials.

6. Since one light bulb in series is the same as one light bulb in parallel, copy the data for the first trial into the first row of the “Resistors in Parallel” data table.

5. Again measure the individual and total voltage changes and individual and total currents.

6. Draw circuit diagrams for each trial.

Data Table: Resistors in Parallel

| | | | | | | | | | | |Calculated Resistance |Calculated Power | |Trial |Total |Bulb #1 |Bulb #2 |Bulb #3 |Total |Bulb #1 |Bulb #2 |Bulb #3 |Total |Bulb #1 |Bulb #2 |Bulb #3 | | |VT(V) |IT(A) |V1(V) |I1(A) |Bright |V2(V) |I2(A) |Bright |V3(V) |I3(A) |Bright |RT(() |R1(() |R2(() |R3(() |PT(W) |P1(W) |P2(W) |P3(W) | |1 Bulb | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |2

Bulbs | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |3

Bulbs | | | | | | | | | | | | | | | | | | | | |

Sample Calculations for Trial #3:

Questions: (as always, please cite specific data to support your claims!)

1. How can you prevent overloading and possibly damaging electric meters?

2. For series circuits, why is only one ammeter needed for each of the trials?

3. For two light bulbs in parallel, why were 3 ammeters needed for 2 light bulbs in parallel, and 4 needed for 3 light bulbs in parallel?

4. Explain why the voltmeter must be moved in series circuits but not for parallel circuits.

5. When bulbs are connected in series, what is the relationship

Between the individual and total voltages? What formula expresses this concept?

Between the individual and total resistance? What formula expresses this concept?

Between the individual and total currents? What formula expresses this concept?

Between the individual and total power? What formula expresses this concept?

6. When bulbs are connected in parallel, what is the relationship between the individual and total voltages?

Between the individual and total voltages? What formula expresses this concept?

Between the individual and total resistance? What formula expresses this concept?

Between the individual and total currents? What formula expresses this concept?

Between the individual and total power? What formula expresses this concept?

6. When more bulbs are connected in series

• Does the resistance of a single bulb change? Why?

What happens to the amount of current coming from the power supply? Why would this happen?

What happens to the power output of the power supply?

What happens to the brightness of an individual light bulb? What happens to the total brightness of all the light bulbs combined?

6. When more bulbs are connected in parallel,

• Does the resistance of a single bulb change? Why?

What happens to the amount of current coming from the power supply? Why would this happen?

What happens to the power output of the power supply?

What happens to the brightness of an individual light bulb? What happens to the total brightness of all the light bulbs combined?

6. When you plug in lights in your house, are they connected in series or parallel? Explain why it is done this way.

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