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Electricity is Exciting! for Fifth Graders Warning! Electricity can be dangerous. ALWAYS have an adult help you experiment. NEVER, ever play with the electric outlets at home! Charge An Electron Voltage “Stack” of Charges Current Moving (Flowing) Charges 1. Charges and Currents a. Wires are made of copper. Copper Electrons are Green. b. Some Copper electrons from the wire get stuck in the potato when the current moves through the potato. What color is the spot near the positive part (anode) of the battery? + is _____________ c. What color is the spot near the negative (cathode) part of the battery? - is ____________ 2. Electrical Engineers use a Digital Voltmeter Meter (DVM) for measuring Get your (yellow) DVM ready to measure Voltage: a. Connect the Red DVM Cable to the VmA hole. b. Connect the Black DVM Cable to the Com hole. c. Turn the Dial in the middle to the DCV 20 Spot. 3. Measuring Voltage: Measure the Voltage of one Battery: a. Touch the Red DVM cable to + terminal of the battery (the top). (Push hard enough.) b. Touch the Black DVM cable to the – terminal of the battery (the bottom). c. What is the Voltage of one battery? V1=__________ Volts d. Now measure the other battery. What is its voltage? V2=_____________ Volts 4. Voltages in Series Add What should we get? a. Write down V1 and V2 that you measured before. b. Add them up. Now tape the batteries together in Series as shown. c. Measure the voltage of the two batteries in series. Write your answer here. Compare your results. Are your calculations and measurements the same? They should be close. Sometimes they are not exactly the same, because measurements are never perfect. 4. Resistance Resistance slows the flow of current. Resistors “eat” charges and turn them into heat. a. Find the 100 resistors. They have four stripes (brown-black-brown-gold). b. Find the 1000 resistors. They have four stripes (brown-black-red-gold). Get your DVM ready to measure resistance. c. Turn the DVM dial to 2000 . d. Connect (touch hard) the DVM cables to each side of the resistor. Measure your resistors e. Measure the 100 resistors and write their resistance above. f. Measure the 1000 resistors and write their resistance above. Experiment: Does it matter which way you turn the resistor around? 5. Resistors in Series a. Electrical Engineers use Protoboards to Design and Test their Circuits. When two wires are in the same row, like these are, they are connected inside the protoboard. b. Connect two resistors in series. Calculate and measure the series resistance. c. When you put two resistors in series, is the total resistance larger or smaller than the original resistors? __________________ 6. Resistors in Parallel Resistors in parallel ( || ) are side-by-side on the protoboard. They combine in a different way, shown above Experiment with several different resistors in parallel. R1 100 1000 100 R2 100 1000 1000 R1||R2 Calculated 50 500 90.9 R1||R2 Measured Is the resistance of two parallel resistors always: a. Larger than both resistors b. Smaller than the biggest resistor c. Smaller than either resistor 7. Light Emitting Diode (LED) Circuit An LED is a resistor that turns charges into light. a. Find the FLAT side with the BLACK leg, and put it in the protoboard as shown. b. Tape wires on the ends of your batteries. c. Connect the + part of the battery to the round side of the LED. d. Connect the – part to the flat side of the LED, as shown. What happens? 8.How can you control the light from the LED? a. Put a 1000 resistor in series with the LED as shown. What happens to the light? b. Challenge: Try different combinations of resistors in series and parallel until you can get the most light from your LED and the least light from your LED. Reducing the current through the LED will reduce the light it puts out. You can reduce the current by putting a resistor in series with it. Hint: Ohm’s Law (like the law of gravity for electrical engineering) say: Current = Voltage Resistance. For less current, should you use more or less resistance? 9. Sum of Voltages V2 V4 In a circuit, all of the voltages will always add up to the voltage you put on the circuit. Test this theory: a. Connect three resistors in series with the LED. b. Measure the voltage across each resistor (and the LED) in the circuit. Be sure you only connect the DVM across the resistor where you are measuring the voltage (see V2, for instance)