Unit 1 1. The diagram below shows a battery and two bulbs in sockets. Sketch connecting wires in a way that would allow both bulbs to light at the same time. 2. Using your diagram from question #1 above, draw arrows to show where and in what direction charge moves. Arrows should clearly indicate the existence of a continuous circular conducting path. The direction of the arrows should represent conventional charge flow; into the negative end of the battery, and out of the positive end. 3. Describe what will happen if one of the bulbs in your diagram is removed from its socket. Explain your reasoning. The second bulb will go out because the continuous conducting path will have a break in it. 4. What is the difference between conductors and insulators? Based on the experience using the Testing Circuit: A conductor allows charge to flow through it. An insulator does not allow charge to flow through it. 5. Draw a diagram of a testing loop which could be used to determine whether or not an object is a conductor. Explain how to use it to identify conductors. See Figure 1.8 Testing Circuit. When a conductors takes the place of the 'something' in the circuit, the bulbs light. When an insulator is the 'something', the bulbs do not light.
6. Examine the diagram at right showing a battery and three bulbs without sockets. You have two wires available. Draw a continuous conducting path that will enable all three bulbs to light. Use arrows to indicate the continuous conducting path through the wires and the bulbs. The student must show the conducting path going into one end of the bulb, through the filament, out the side of one bulb into the side of the other, out the other end and through the battery. 7. Figures 2 through 6 show a variety of possible connections with one battery, wires, and two bulbs. For each figure decide which, if any, bulbs will light and draw a line showing the continuous conducting path. 1 1 2 2 Figure 2 Figure 3 Bulb 1: Unlit Bulb 2: it Bulb 1: it Bulb 2: it
1 2 1 2 Figure 4 Figure 5 Bulb 1: it Bulb 2: Unlit Bulb 1: it Bulb 2: Unlit 1 2 Figure 6 Bulb 1: Unlit Bulb 2: Unlit 8. Describe evidence which indicates that bulbs light only when something is happening in the wires. Students should cite their observation that the deflection of the compass and the lighting of the bulbs occur simultaneously as soon as the circuit is complete.
9. Indicate whether each of the following statements is True or False. Then state evidence which either supports or contradicts each statement. [a] The battery determines the direction of flow of charge in a circuit. True. If the wires connected to the battery are reversed, the compass needle deflection will also be reversed. [b] A compass can be used to determine the exact direction that charge flows in a circuit. False. A compass can be used to determine relative direction but not absolute direction. [c] ight bulbs are non-directional devices. (Whichever way they are connected in the circuit, they behave the same way, even if you turn them around.) True. The brightness is the same even if you turn the bulb around. (And the brightness is the same even if you turn the battery around.) [e] Non-metal substances are generally conductors. False. The testing circuit provided evidence that metals are conductors, and that non-metals are insulators. (Pencil lead, made of graphite, was an exception - a non-metal that conducted.)
Unit 2 1. Draw a diagram of the structure of a capacitor and describe it in words. See Figure 2.4. A capacitor consists of two very large plates of conducting material and an insulating material between the plates. The plates are rolled up and have a terminal attached to each so that electrical connections can be made. 2. How do you know that the charge flow during capacitor discharging is in the opposite direction of charge flow during charging? Describe an experiment to show this. Charge and discharge the capacitor after lining up a wire with the needle of a compass. The reversal of needle deflection shows that the direction of flow is reversed. 3. A visual representation of a circuit is shown below. On the right, sketch the corresponding schematic diagram. 4. Based on your lab activities and class discussion, draw arrows to indicate the direction of charge flow when the circuits below are first connected during charging (as in Figure A) and during discharging of the capacitors (as in Figure B). Figure A Figure B
5. How are a Genecon and a battery similar when they are connected to a circuit? How are they different? Use the terms "charge" and "energy" in your comparison. Both cause charge to move around the circuit and mobile charge is a normal constituent of both. But a Genecon uses an external energy source to make charge move in a circuit, while a battery uses an internal energy supply to make the same thing happen. 6. Compare the similarities and differences between a capacitor in a circuit and the air capacitor you used in class. Similarities: When air enters one side of the air capacitor, air leaves the other side but it's not the same air. When charge enters one side of a capacitor, charge leaves the other side. No air passes through an air capacitor; no charge passes through the insulation in an electric capacitor. Differences: An air capacitor has a flexible membrane (balloon) insides which expands when the air capacitor is 'charged' or filled with air; the electric capacitor does not have any moving parts. 7. When a capacitor is discharged, where does the charge "go back to"? The charge goes back to the other capacitor plate and other conducting parts of the circuit where it was pumped from during the charging process.
Unit 3 1. A battery is connected to two identical low-resistance bulbs (A and B) in series. Make a schematic diagram of this circuit, and add arrowtails and starbursts. A B Same current throughout the circuit. 2. For this question, refer to the circuit in Question 1. For each of the following statements: If the statement is true, write the letter T in the space provided. If the statement is false, change the statement so that it becomes true. a. Charge flows at the same rate through bulb A and bulb B. b. Bulb A uses up some moving charge, so less reaches bulb B. c. If bulb B is removed from its socket, bulb A will go out. d. When the circuit is connected, bulb A lights before bulb B. e. A battery is needed to light the bulbs because it is the source of the moving charge. f. Bulb A will be brighter than bulb B. a. T b. F (Charge is never "used up".) c. T d. F (Both bulbs light at the same time.) e. F (A battery is needed because it contains stored energy, which is transformed to heat the bulb filaments. The moving charge originates in all conducting matter.) f. F (The bulbs will be equally bright.) 3. You are given two new bulbs. When used in a circuit to charge and discharge the blue capacitor you note that these new bulbs stay lit longer than the long bulbs had (using the same battery and capacitor). Do the new bulbs have a higher or lower resistance than long bulbs? Explain your reasoning. Higher resistance. The longer lighting time indicates a decreased flow rate.
4. In the circuit shown, a compass is placed under a wire at point A A. Draw an arrowtail by the compass to show flow rate, and starbursts on the bulbs to show brightness. For each of the changes listed below, draw a new circuit with arrowtails and starbursts appropriate for indicating the effects of the change. #1 #2 Figure 4 a. The two bulbs from Figure 4 are replaced in parallel to each other. b. A third round bulb is added in series with the bulb in Figure 4. a. increase in both brightness and flow rate -- because there is now less total resistance. b. decrease in both brightness and flow rate -- because there is more total resistance 5. Compare the resistance of a bulb and a wire. Cite two observations as evidence to support your comparison. Adding more wires in series with a lit bulb will not change the bulb brightness. Shorting out a bulb causes a second bulb in series to become much brighter. A capacitor requires much less time to discharge through a wire than through bulbs; therefore the wire much less resistance. 6. A capacitor is charged through two bulbs (Figure 6a) and then discharged through a single bulb (Figure 6b). Figure 6a Figure 6b Show appropriate starbursts and arrowtails for each circuit Mark each of the following statements as True or False (T or F). If a statement is False, re-write it as a correct statement. a. Charge flows at a greater rate through the single bulb than through the two bulbs. b. More charge flows through the single bulb than through the two bulbs.
c. The same amount of charge flows during charging and discharging. d. The single bulb shines brighter than either bulb in the two-bulb circuit. e. The total resistance of the two bulbs is less than that of the single bulb. f. A compass would show a larger deflection for Figure 6a than for Figure 6b. g. The brightest bulb(s) indicate the fastest charge flow. Wider arrowtails and starbursts with more rays in Figure 6b. a. T, b. F - Same total amount of charge through both, c. T, d. T, e. F - More than, f. F - arger deflection for Figure 6b, g. F - The brightest bulb indicates the greatest flow rate. 7. Consider two circuits containing identical components (batteries, bulbs, wires). In Circuit S, the two bulbs are in series. In Circuit P, the two bulbs are in parallel. Which circuit (S or P) is described by each of the statements below? a. The circuit with the most total resistance. b. The circuit with the greatest flow rate of charge through the battery. c. The circuit with the greatest conductance. a. S; b. P; c. P.
Unit 4 1. In terms of electric pressure, describe a charged capacitor. A charged capacitor has higher-than-normal electric pressure on one plate because of excess charge, and lower-than-normal pressure on the other plate because of depleted charge. The amount of pressure difference depends on the pressure difference of the terminals of the battery used to charge the capacitor. 2. In terms of electric pressure, explain why a capacitor stops charging. A capacitor stops charging when the compression of charge in its (+) plate raises its pressure to that of the high-pressure source (a battery, another capacitor) connected to it, and when the depletion of charge in the (-) plate lowers its pressure to that of the low-pressure source connected to it. 3. For this question, assume that you start with a circuit containing a battery, two long bulbs and a charged capacitor (Figure 3a). Figure 3a CHAGED CAPACITO Figure 3b SECOND BATTEY ADDED Predict what you would observe when an additional identical battery is added to the circuit in Figure 3a (as shown in Figure 3b): The bulbs will light as brightly and for the same length of time as when the capacitor was first charged. Explain your reasoning: The difference between the electric pressures on the outer battery terminals is now twice what it was before. Additional charge must travel to and be compressed in the (+) capacitor plate, and leave the (-) capacitor plate before the pressure difference between the plates is again equal to the pressure difference between the battery terminals.
4. Use color-coding to determine the order of brightness of the bulbs in the circuits below. ank the three bulbs "A", "B", and "C" from brightest to dimmest. All seven bulbs are identical. C A B BIGHTEST DIMMEST Pressure differences in colors bulb A: red-to-blue; bulb B: yellow-to-blue; Bulb C: red-to-orange;. The ranking is: A, B, C 5. Color-code the diagram below. Predict which bulbs will light, if any. Wires adjacent to the positive terminal are red. Wires adjacent to negative terminal are blue. Both bulbs light; both are very bright (red to blue pressure difference). 6. Color-code the diagram below; predict which of the three bulbs will light, if any, and indicate brightness. All three bulbs light, equally bright (red to blue pressure difference).
7. All bulbs and batteries in the two circuits below are identical. B C A a. Color-code both circuit diagrams. b. ank the three bulbs A, B, C in order of brightness from brightest to dimmest. Brightest B A C Dimmest
Unit 6 1. Some students insist on connecting their voltmeter incorrectly in a circuit. Explain how the voltmeter should be connected, and why. A voltmeter should be connected in parallel; it has a very high resistance; if it is placed in series within a circuit it will drastically reduce the current and 'interfere' with the circuit. 2. In which circuit will the ammeter measure the current through the long bulb? Circle one: A B Neither A A Figure A Figure B Figure A. 3. Describe the changes, if any, in each voltmeter reading during charging of the capacitor. V1: Across the battery - reading will remain constant. V2 V2: Across the bulb - reading will increase suddenly from zero to a maximum and then return to zero. V3: Across the capacitor - reading will increase steadily from zero to a maximum. V 1 V3
4. Complete the diagram below with the correct pressure-difference values for each component by recording them in the spaces provided. Note that the voltmeter place around the battery has a readout of 3 V. V= V= V= 3V V= V= V= V= V across each long bulb = 1 volt. V across all three long bulbs = 3 volts. V across each round bulb = 1.5 volts. 5. Two bulbs are connected in series. Bulb A is receiving energy at the rate of 15 watts and Bulb B at 40 watts. Indicate which bulb is described: a. The resistance of the bulb is larger. b. The current through the bulb is greater. c. The light from the bulb is brighter a. B b. neither; same current through both bulbs c. B 6. You are given two circuits with identical batteries. In one circuit (S), a round and a long bulb are in series. In the other (P), the same bulbs are in parallel. Indicate in which circuit: a. the battery is giving out energy at a greater rate. b. the long bulb is converting energy to heat and light at a greater rate. c. the round bulb is converting energy to heat and light at a greater rate. a. Parallel b. Parallel c. Parallel
7. Consider the circuit at right, containing five identical bulbs. P (a) Where is it least current flow - through Point X, Y, or Z?? (b) If a shorting wire is placed across bulb #1, what will be the effect on each of the other bulbs? 1 2 3 4 5 (c) If a shorting wire is placed across bulb #4, what will be the effect on each of the other bulbs? X Y Z a. The current is least through Point Y. b. All bulbs will become dimmer. c. All bulbs will go out. 8. In the circuits below, all bulbs are identical. For each of the following pairs of bulbs, circle the letter of the bulb you predict would be the brighter of the two, or circle "nearly the same brightness". A B C E F D G (a) A and C A C Nearly the same brightness (b) D and E D E Nearly the same brightness (c) B and D B D Nearly the same brightness (d) D and F D F Nearly the same brightness (e) C and G C G Nearly the same brightness (f) B and G B G Nearly the same brightness (g) C and E C E Nearly the same brightness
a. Same b. E c. D d. Same e. C f. G g. Same