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PHYS 100 Dr. Labroo Introductory Physics Laboratory V_F02 Experiment 8: Charges, Currents and Simple Circuits Objectives: 1. To investigate the nature of static electricity. 2. To build a continuity tester and classify materials as insulators or conductors. 3. To investigate the properties of series and parallel circuits. Suggested Reading: Pages 373 – 392 (Ch. 21) and 399 – 412 (Ch. 22) of the text. Equipment and Supplies: Glass rod and wool, ebony rod and fur, electrometer, some common materials, light bulbs, wires, switch, current meter, and a current source. Introduction: Electric charge, like the mass, is an inherent property of matter. But unlike mass, charges can be positive (protons) or negative (electrons). When brought close to each other, these charges exert forces on each other. This kind of force, called the Coulomb force depends on the magnitude of the charges and the separation distance between them. Unlike the gravitational force, which is only attractive, the electrostatic force can be either attractive (between unlike charges) or repulsive (between like charges). When charges flow through an electrical conductor, they form an electric current. Insulators, on the other hand, offer a very high resistance to the flow of charges. It takes a battery to get the charges flowing through a circuit by creating a potential difference between the battery terminals. In a circuit, charges always flow from a higher potential to a lower potential in pretty much the same way as water flows from high pressure to low pressure. The amount of current flowing through a circuit depends on the potential difference (Voltage) of the battery and the resistance of the circuit. This is called the Ohm’s Law and it is written as follows: Current Votage Resistance Power consumption of an electric circuit depends on the applied voltage and the total current through the circuit. Power = Voltage x Current Light bulbs (resistors) can be placed in a circuit in two ways: series connection and parallel connection. Among the many activities of this lab, you will learn how to construct a simple circuit and then make series and parallel connections using light bulbs. You will then investigate the properties of these circuits. Procedure: Part I 1. This part is set up as a demonstration by your instructor. Follow the instructions and write down your answers in the data sheet provided. Part II BULB 1. Use a single light bulb from the given circuit board and some wires, construct the circuit as shown here. This is your continuity tester. 2. When you connect the open end the light bulb should light up. 3. Place various materials provided to you between the open ends of your tester and see if the bulb lights up or not. Write down your observations in the table. BATTERY + - OPEN END Part III Series Circuit Parallel Circuit 1. Using the picture shown above, construct the series circuit for the bulbs. 2. Note the current while adding bulbs to the circuit. 3. Calculate the circuit resistance and power by using the appropriate formulas. The applied voltage is 6 Volts. 4. Make a graph of current versus number of light bulbs from your data. 5. Do the remaining things you are asked to do in the data table and write down your answers. 6. Repeat steps 1 through 5 for the parallel circuit. Questions: 1. When you rub plastic rod on fur, the rod gets negatively charged. a) What charge, if any, does the fur acquire? b) What do you think would happen if the plastic rod and fur were then brought back into contact with each other? 2. Consider your data from Part II. Do you notice anything common between conductors? Explain your answer. 3. Compare the series circuit to a parallel circuit. In which circuit does a greater amount of current flow? Which consumes more energy? Which circuit offers a greater resistance to the current flow? 4. If you turn off your TV at home, it does not affect the working of other appliances. Based on this, how do you think the appliances are wired in your home? Report Requirements: Brief summary of the experiment, data, and answers to the above questions. PHYS 100 Laboratory Data Sheet 1 Name: Experiment 8 Partners: Part I: Describe what happens to the electroscope when: A negatively charged plastic rod is touched to the metal top. Briefly explain why? A negatively charged plastic rod is brought close to the negatively charged electroscope. Why? A positively charged glass rod is brought close to the negatively charged electroscope. Why? Part II: Material Paper Iron Plastic Wax Aluminum Copper Wood Insulator or Conductor? PHYS 100 Laboratory Data Sheet 2 Experiment 8 Part III: Series Circuit Number of Light Bulbs Current (Amperes) Circuit Resistance (Ohms) Parallel Circuit Power (Watts) Number of Light Bulbs Current (Amperes) Circuit Resistance (Ohms) Power (Watts) 1. Compare the overall brightness of light bulbs in parallel and series circuit. In which circuit are the bulbs brighter and why? 2. What happens to the brightness of the other bulbs, when you remove (unscrew) one bulb from the circuit? In each case explain why. Series circuit: Parallel circuit: 3. What happens to the brightness of the other bulbs when you short circuit (see figure below) one of them? In each case explain why. Series circuit: Parallel circuit: Short circuit: Connect a wire across the bulb, like so…