Physics 2

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Lab Activity: Basic Circuit Analysis

There are two parts to this activity. The first is a hands-on investigataion with simple lightbulb circuits. The second is a video lab activity. Both activities have the same goal: To learn how to analyze simple electrical circuits. Your lab report should include both parts of this investigation.

Part 1: Lightbulb Circuits

In this part of the lab you will investigate the effect of various circuit designs on the brightness of light bulbs. You learned in the previous presentations that current, voltage, resistance and power are important electrical properties. Incandescent light bulbs are made of resistors (filaments) that can give off heat and light when conducting electrical current. The rate at which the bulb gives off heat and light is power (P = IV = I2R = V2/R). The “brightness” of a bulb can thus be used as a rough measure of the power dissipated by the bulb. For light bulbs of the type you will be using in this lab a minimum voltage is required before the light bulb will be bright enough for a human to see.

IMPORTANT: If the resistance of all the bulbs are the same (you can assume that in this activity), then the brightness can also be used to give a rough measure of voltage (P = V2/R) for each bulb.

Materials Needed:
Two AA batteries (1.5 volt, Alkaline)
Two AA battery holders
10 pack of 14 inch jumper wires with alligator clip ends
(any copper wire will do, but without alligator clips the circuit connections are difficult to maintain)
4 flashlight bulbs
4 bulb holders
These materials can be purchased at myscience-prep.com. Goal: By connecting the bulbs and batteries in a wide variety of ways, draw several conclusions about how the brightness (power) of the bulbs are affected by how they are connected to each other and to the batteries.

Use the equipment to create the circuits shown below. Make observations about the brightness of each bulb in each circuit (and how the brightnesses compare from circuit to circuit. You can use the brightness of the single bulb in circuit #1 as a "reference" brightness. In other words, you can compare other brightnesses to it.). Record these observations in table form in your lab notebook.

Notes: The connection points on the bulb holder are shown below. Also, be sure to connect the battery poles as shown (+ to -).    Once you have completed the work and made your observations, answer the questions below. Assume that all the bulbs have the same resistance. Base your answers on your observations and the forms of Joule's Law that you already learned:

P = IV = I2R = V2/R

1. Which bulbs (in the circuits you constructed) have the greatest voltage? Which have the lowest voltage?
2. How do the voltages of the bulbs in circuit #3 compare to the voltages in circuit #2?
3. How do the voltages of the bulbs in circuit #5 compare to th voltages of the bulbs in circuit #6?
4. How do the brightnesses of the bulbs in circuit #3 compare to those in circuit #6? Give a reason for your answer based on how the circuits are constructed.
5. In your own words, give a reason why the bulbs in circuit #3 do not have the same brightness as the bulbs in circuit #2
6. In the previous practice problem set, you learned that resistivity is affected by temperature. How do you think the observations in this lab could be affected by that fact?