Exploration 1: Light the bulb

Transcription

1 Part One: Properties of Electric Circuits Exploration 1: Light the bulb Most of us have heard the word circuit, but few of us have a clear idea of what it actually represents. In this section we will develop a model - an idea in our minds - of what we mean by the word circuit. Equipment: 1 round bulb (1.5 V) 1 connecting wire 1 D battery Part A: Light the bulb! Using only the single wire and the battery, light the small bulb Draw the arrangement that you used to light the bulb, below. Be specific about which parts of the bulb and battery you touched with the wire: Part B: How charged particles travel Equipment: Battery pack with 2 D batteries Connecting wires (leads) 2 round bulbs, one in a base Empty bulb base 1 large light bulb (for observation only) empty base The circuit used in Exploration 1 can be thought of as a testing circuit for determining the existence of a conducting path in the wires, because the bulb 1

2 Part One: Properties of Electric Circuits glowed. This test will help us determine if there is a conducting path through the bulb itself. Set up the circuit shown above. Complete the circuit using the empty base. Attach the light bulb to the positive terminal and the empty base to the negative terminal. Does the bulb light? Maybe it is not hooked up correctly. Switch the leads. Attach the light bulb to the negative terminal and the empty base to the positive terminal. Did the bulb light? Why or why not? Put the bulb into the empty socket. Describe what happens: Switch the leads again, so the original bulb is attached to the positive terminal and the new bulb to the negative terminal. Does it make any difference? Draw a diagram that clearly illustrates the conducting path through the bulb. Examine the larger light bulb. Two wires extend from the filament of the bulb into the base. Note that there is a metal tip, separated by an insulating material from the rest of the base. Based on your experiments, above, draw a diagram of the light bulb, showing where the wires attach. 2

3 Part Two: Origin and Movement of Charge Exploration 2: Schematics Before continuing in our investigations of electric circuits we need to develop a shorthand notation for electrical elements. Schematics are a shortcut method of showing how the circuit elements are to be connected. Schematics of circuits are always shown in technical manuals and other materials including textbooks. The diagram below compares the pictorial diagram or real world representation of the circuit you built in Exploration 1 with the schematic, or physics representation, of the same circuit. Can you identify the symbols used for each of the elements in the circuit? To be able to read or draw a schematic you will need knowledge of what symbols are used to represent the various elements in an electric circuit. These symbols are fairly universal a schematic drawn in Asia will look the same as a schematic drawn in the US, as long as the circuits are the same. The table below shows some of the basic schematic symbols used in this module. capacitor Long line is positive

4 Exploration 3: Detecting Activity in Wires Is anything happening in the connecting wires when a circuit is completed? We are going to use a magnetic compass, the type used to determine geographic directions, as a tool to help us answer the question just posed. Equipment 2 sockets 2 identical round bulbs Connecting wires Battery Pack 2 batteries Liquid-filled compass Masking tape to tape down compass 1. Construct the circuit shown in the figure above, except leave one of the wires to the battery disconnected while you place a compass under the middle connecting wire (the wire between the two bulbs). Keep the compass away from any metal such as table legs and the battery cells. Tape the compass to the table, so it won t move. 2. Orient the connecting wire above the compass so that it is parallel to the compass needle. The compass needle and wire will be oriented in a north/south direction. For consistency in observations between different groups in the class, make sure that the compass needle points toward the positive end of the battery pack, as seen in the diagram. One person should hold the wire to make sure it remains parallel to the needle and rests on the top of the compass case. Does the wire seem to have an effect on the compass needle while the circuit is not connected? 3. Observe the effect on the compass needle as the final wire is connected to complete the circuit. What happens? Record both the direction and approximate amount of the compass deflection. NOTE: When reporting the compass deflection, describe its 4

5 action in terms of a clockwise or counterclockwise rotation. Using such terminology will allow us to compare results with others with less confusion. 4. Without moving the compass, disconnect and reconnect different connecting wires to be sure that the effect is reproducible. Is the same effect noted no matter which wire is disconnected and then reconnected? Record your observations (amount of deflection, direction for each wire). 5. Without moving the compass, move the circuit. Does the magnitude/direction of deflection depend on which wire it is?. 6. Without moving the compass, disconnect the battery and take one of the batteries away. Reconnect the circuit and record your observations. Does the magnitude or direction of deflection change? If so, how? 7. What effect, if any, do you think reversing the connections to the battery pack would have on compass deflection and bulb brightness? Explain.- 8. Reverse the connections to the battery pack without moving the compass or anything else in the circuit. You may find it easiest to disconnect the wires from the battery pack, turn the battery pack around, and reconnect the wires. Record your observations regarding amount, direction of compass movement and bulb activity. Did they agree with your predictions? 5

6 9. Write a paragraph describing the relationship between the compass deflection and the lighting of the bulbs. Also compare the activity in each of the connecting wires as implied by the compass deflections. Exploration 4: Capacitors Equipment 2 capacitors (25,000 μf) 6-volt bulbs (blue base) Connecting wires Battery Pack 8 AA batteries Stopwatch multimeter charging + - discharging Experiment 1: One capacitor and one bulb Make sure capacitor is uncharged before starting the experiment by briefly connecting the capacitor terminals with a wire (repeat at the start of each experiment). 1. Connect the charging circuit shown above. Make sure the positive terminal of the capacitor is connected to the positive end of the battery pack and same for negative terminals. While still connected, measure and record the potential difference across a) the battery pack terminals and b) the capacitor terminals. V bat V c 6

7 Record your observations of the light bulb below. Why did this happen? Answer by comparing the potential difference of the capacitor with the potential difference of the battery pack and how that influences the charge flow. 2. Remove the battery and reconnect one light bulb. Use the stopwatch to measure how long it takes for the light to go out. Make a mental note regarding the brightness of the bulb because you will be comparing the brightness to other circuits. s 3. Explain what happened as the bulb lit up and then went out, in terms of charge and potential difference: 4. Calculate the amount of charge stored by the capacitor: C Show your work. 7

8 5. Calculate the energy stored by the capacitor: J Show your work. Experiment 2: Two capacitors in parallel and one bulb 1. Connect the capacitors in parallel (diagram shown below) and charge as before. This procedure doubles the capacitance of the circuit. It is not necessary to connect the bulb for the charging procedure. 2. Measure the voltage across the battery, and across each capacitor after charging. How do they compare? 3. Remove the batteries and connect the light bulb. Measure the time it takes for the light to go out s Compare the time and brightness with those from Experiment 1 (Repeat Experiment 1 if you need to compare the brightness). 8

9 4. By what factor has the amount of charge stored on the 2-capacitor system changed, compared with the charge stored in Experiment 1? Q 2 /Q 1 = 5. By what factor has the amount of energy stored on the 2-capacitor system changed, compared with the charge stored in Experiment 1(add the energies of each capacitor)? EPE 2 /EPE 1 = Experiment 3: One capacitor and one bulb with half ΔV 1. Change the battery pack to ½ the original voltage by a. Removing the battery opposite to the positive terminal. b. Disconnecting the negative terminal and reconnecting the black lead to the metal hole at the now empty space (ask if you need help). Now charge the capacitor. 2. Remove the batteries and connect the light bulb. Measure the time it takes for the light to go out. s Compare the time and brightness with those from Experiment By what factor has the amount of charge stored on the lower voltage system changed, compared with the charge stored in Experiment 1? Q 3 /Q 1 = 4. By what factor has the amount of energy stored on the lower voltage system changed, compared with the charge stored in Experiment 1? EPE 3 /EPE 1 = 9

10 Experiment 4: Two capacitors in parallel, one bulb, half ΔV 1. Connect the 2 nd capacitor in parallel with the first and charge as before. 2. Remove the batteries and connect the light bulb. Measure the time it takes for the light to go out s Compare the time and brightness with those from Experiment 1: 3. By what factor has the amount of charge stored on this system changed, compared with the charge stored in Experiment 1? Q 4 /Q 1 = 4. By what factor has the amount of energy stored on this system changed, compared with the charge stored in Experiment 1 (add the energies of each capacitor)? EPE 4 /EPE 1 = 5. Based on the results of this experiment, do you think the time it took for the bulb to go out was a function of the charge stored, or the energy stored? Explain your answer. 6. Based on the results of the this experiment, do you think the brightness of the bulb was a function of the charge stored, or the energy stored? Explain your answer. 10

11 Check your Understanding 1. For each of the situations illustrated below, draw either the schematic or the pictorial representation of a circuit, depending on the representation shown. 1. Pictorial or real world representation 1. Schematic or physical representation 2. Pictorial or real world representation 2. Schematic or physical representation +bat- capacitor 3. Pictorial or real world representation 5. Schematic or physical representation 2. For each of the sets of connections shown on the next page: a. Decide which bulb(s) in each figure will light. Record the bulb number on the lines provided below the figures. b. On each diagram, draw in the conducting path for moving charges for each circuit. Your paths should include the battery and should indicate which bulbs will be lit. c. Draw the schematic or physical representation for each figure in the space at the bottom of the page. 11

12 Indicate which bulb(s) will light, if any: Figure 1 Figure 2 Figure 3 Figure 4 Make your circuit diagrams here. If the circuit is not complete, draw a space between the bulbs. If the bulbs light, show connection between bulbs with a connecting line. 12