Science Olympiad Shock Value ~ Basic Circuits and Schematics

Transcription

1 Science Olympiad Shock Value ~ Basic Circuits and Schematics Use a single D battery, a single bare wire and a light bulb. Find four different ways to light the light bulb using only a battery, one wire and the bulb. Sketch the four different ways on the battery drawings shown below. 1. What are the two important parts of a battery that must be used in order to make the bulb light? 2. What are the two important parts of a light bulb that must be used in order to make the bulb light. 3. What is meant by a circuit? Use a single D battery, two bare wires and a light bulb. Find a way to light the light bulb using the battery, two wires and the bulb. This time the light bulb may not touch the battery. Sketch the circuit on the battery drawing shown at the right. Shock Value 1 Demos

2 8. Wire a complete circuit using a battery holder, switch, socket, battery, wires, and light bulb. Draw this circuit. 9. What is a switch? How does a switch work? Instead of drawing a diagram, we have developed schematic symbols to illustrate different circuits. 10. Make a table of the schematic symbols for a battery, light bulb, open switch, closed switch, wire, and junction. (The rest of these will be revealed in a later activity) battery ammeter light bulb voltmeter switch - open wire switch - closed junction (wires connected) resistor rheostat 11. Draw a schematic drawing of the circuit that you wired and sketched in #8 with the switch closed. 12. Draw a schematic drawing of the circuit that you wired and sketched above with the switch open. Shock Value 2 Demos

3 Using meters Using an ammeter An ammeter is an electrical device used to measure the amount of current that flows through a wire. An ammeter is wired in series with the rest of the circuit. To measure the current going through a given wire you have to break the circuit and insert the ammeter so that all current goes through the ammeter and then the rest of the circuit. The ammeter has two terminals, one black and one red. The black terminal is placed in the circuit so that the wire connected to it is closest to the negative terminal of the battery. Closest is decided by following the wire directly from the black terminal through any other devices like light bulbs to the negative terminal of the battery. The red terminal is wired closest (along the wires) to the positive terminal of the battery. This is done as illustrated at below. We are using a D battery placed in a battery holder. If you wire the ammeter backwards the needle will deflect the wrong way. Immediately turn off the switch and rewire the ammeter in the opposite direction or reverse the battery. An ammeter measures How is an ammeter wired in a circuit? What is meant by a series circuit? The symbol for current is The unit for current is Here is a schematic of the circuit that you just wired. Measure the current passing through the circuit and record it on your drawing. In the last circuit the ammeter measured the current before it went through the light bulb. Is the current different after it goes through the light bulb? Make a prediction and explain why you made the prediction. Is: I in > I out I in = I out, I in < I out,? Measure the current. What is true about the current in a simple circuit (the circuit above)? Shock Value 3 Demos

4 Using a voltmeter We are now going to add a voltmeter to the circuit, leaving the ammeter in place. A voltmeter is an electrical device used to measure the potential difference (potential drop or gain) between any two points in a circuit. A voltmeter is wired in parallel with the device that you want to measure the voltage across. To measure the voltage between any two points in the circuit you touch one terminal of the voltmeter to one point and the other terminal to the other point. The voltmeter has two terminals, one black and one or more red. The black terminal is placed in the circuit so that the wire connected to it is closest to the negative terminal of the battery. The red terminal is wired closest to the positive terminal of the battery. This is done as illustrated at the right. A voltmeter measures How is a voltmeter wired in a circuit? What is meant by a parallel circuit? The symbol for voltage is The unit for voltage is Measure the current passing through the circuit (I) and record it on your drawing. Measure the voltage loss across the light bulb (V B ) and the voltage gain across the battery (V S ). You do not need 2 voltmeters. You will measure the voltage from one, the measure the other after that. Voltage gain of the battery V S = Voltage loss of the light bulb V B = How do these two values compare, are they relatively close in value or way off? Why? Shock Value 4 Demos

5 Two bulbs in series Using voltmeters and ammeters to analyze circuits. Wire the circuit shown below with two light bulbs in series. Voltage gain of the battery V S = Voltage loss of the light bulb #1 V 1 = Voltage loss of the light bulb #2 V 2 = How does the voltage gain compare to the sum of the voltage losses, close or not? Explain why. Are the bulbs bright or dim? Two bulbs wired in series and two batteries in series. Wire the circuit shown below with two light bulbs in series and two batteries in series. Voltage gain of the batteries V S = Voltage loss of the light bulb #1 V 1 = Voltage loss of the light bulb #2 V 2 = How does the voltage gain compare to the sum of the voltage losses? Are the bulbs bright or dim? Shock Value 5 Demos

6 Series and Parallel Circuits Wire the circuit shown below with two light bulbs in series and two batteries in series. You have done this one before so this will be good practice. 1. Record the values shown on the schematic. a) Are the bulbs bright or dim? b) With a colored pencil draw the path of the current around the circuit. 2. Unscrew Bulb #1 a) What happens to bulb #1? b) What happens to bulb #2? c) What current passes through the ammeter? 3. Screw bulb #1 back in and predict what will happen when you unscrew bulb #2 4. "Christmas Lights" are often wired in series just like the circuit you just tested. a) What happens when one of the lights burns out? Why? b) We can make a string of lights in series just like the "Christmas Lights." If you were given light bulbs that are designed to operate with a voltage of 14 volts, how many would you have to wire in series before it is connected to a 120-volt outlet? c) If we used light bulbs designed to work with a voltage of 3 volts (long top bulbs we used with the generators), how many would we have to wire in series? What would happen if one were unscrewed or burned out? Wire the circuit shown below with two light bulbs in parallel and two batteries in series. 5. Record the values shown on the schematic. a) Are the bulbs bright or dim? b) Are they brighter or dimmer than the bulbs in the series circuit, #1, at the beginning of this activity? c) With a colored pencil draw the path of the current around the circuit through each bulb. 6. What happens when you unscrew Bulb #1? a) What happens to bulb #1? Bulb #2? b) What happened to the current passing through the ammeter? c) What happened to the voltage drop across Bulb #2? 7. Screw Bulb # 1 back in. What do you think will happen when you unscrew Bulb #2? Do a similar analysis as you did when you unscrewed Bulb #1 How is a home wired? Using what you observed in series and parallel circuits, do you think that your house in wired in series or parallel? Explain your answer. Shock Value 6 Demos

7 Resistance 1. Wire the circuit pictured in the schematic at the right. Use a long piece of copper wire about one meter long. Measure the current passing through the circuit, the voltage gain of the battery, and the voltage loss of the bulb and the long copper wire. Current passing through the circuit: I = Voltage gain of the battery V S = Voltage loss of the light bulb: V B = Voltage loss of the copper wire: V CW = 2. Wire the circuit pictured in the schematic at the right. Use a long piece of nichrome wire to replace the copper wire used in #1. Make sure you spread out the wire so it does not touch itself. Measure the values shown. Current passing through the circuit: I = Voltage gain of the battery: V S = Voltage loss of the light bulb: V B = Voltage loss of the nichrome wire: V NW = 3. Compare the current passing through the circuit in #2 compared to #1? 4. Compare the voltage drop across the nichrome wire as compared to voltage drop across the copper wire? 5. What happened to the brightness of the bulb when the nichrome wire was used? 6. Which wire is a better conductor of electricity? 7. Which wire has more resistance? 8. What do we mean by resistance? 9. What is the unit for resistance? 10. What is the schematic symbol for a resistor? Shock Value 7 Demos

8 11. Complete the following table. Length of wire A. Start with the circuit that you already wired with the long nichrome wire. Full B. Loosen the screw on the meter and shorten the nichrome wire so that it is one half its original length. 1/2 C. Shorten the nichrome wire so that it is one quarter of its original length. 1/4 D. Shorten the nichrome wire so that it is one eighth of its original length. 1/8 Current - I amps Brightness of bulb 12. How does a dimmer switch work? 13. Take out the nichrome wire from your circuit and insert a dimmer switch to complete the circuit. Turn the knob on the dimmer switch and see what happens to the light bulb. 14. What is a rheostat (dimmer switch)? 15. a) What is the schematic symbol for a rheostat? b) Draw a schematic of a circuit with a battery, light bulb and a rheostat (dimmer switch). Shock Value 8 Demos

9 What is a "short" or a short circuit? Wire the circuit at the right and read the meters to get the following measurements. Potential gain at the batteries. Current passing through the circuit. Place a wire between the terminals of bulb #1, as shown at the right. Measure the values shown. 1. What happens to each of the following? a) the current, I? b) Bulb #1? c) Bulb #2? d) The voltage across the battery, Vs? e) From what you learned explain what happened and why. Use a higher range ammeter, 0-5 amps and then place a wire between the first terminal of Bulb #1 and the last terminal of Bulb #2, as shown at the right. Measure the values shown. Do not leave this wired too long, so turn off the switch as soon as you get your readings. 2. What happens to each of the following? a) the current, I? b) Bulb #1? c) Bulb #2? d) The voltage across the battery, Vs? e) From what you learned explain what happened and why. Shock Value 9 Demos

10 OK, we learned that our homes are wired in parallel. So what happens when we have a short in a parallel circuit? Use a higher range ammeter, 0-5 amps 4. Wire the circuit at the right and measure the current coming from the battery and the potential gain across the batteries as shown. a) the current, I? b) The voltage across the battery, Vs? c) Use a colored pencil to show the path(s) taken by the current. 5. Place a wire between the terminals of bulb #2, as shown at the right. Measure the values shown. a) the current, I= b) The voltage across the battery, Vs= c) What happens to bulb #2? d) What happens to bulb #1? e) Why does this happen? f) Using a colored pencil show which way most of the current goes when there is the short. g) What is a fuse? What is a circuit breaker? Shock Value 10 Demos