POWER and ELECTRIC CIRCUITS

Transcription

1 POWER and ELECTRIC CIRCUITS Name For many of us, our most familiar experience with the word POWER (units of measure: WATTS) is when we think about electricity. Most of us know that when we change a light bulb, we check it s WATTAGE. In the following activity, we will SEE how POWER can come from electricity. First, remember what POWER is: The amount of WORK done divided by TIME. In other words, if you do work faster (in less time) then the POWER is higher. If you do work slower, then the POWER is less; so how fast you work determines power! Activity: Building Electric Circuits For this activity, click the link labeled Electric Circuits on Mr. P s website or go to Choose OPEN or RUN; DO NOT CHOOSE SAVE. Pop-up: Select Circuit Construction Kit (DC ONLY) PART 1: THE SERIES ELECTRIC CIRCUIT Procedure: 1. Build the circuit shown here using the parts from the right-hand side of the screen. The circuit should include: - one battery PUT THE BATTERY IN AS SHOWN!!!! - one switch - one light bulb - 6 wires 2. Close the switch and observe that the light bulb lights up! If not, make sure all the parts are actually connected: NO RED CIRCLES WHERE THE PARTS CONNECT. Notice the electrical FLOW as well as the glowing light bulb! VERY IMPORTANT NOTE; YOU MUST READ THIS NOTE TWICE: This simulation let s you see something that is not normally easy to observe. Electricity happens because electrons flow in the wires and other parts of the circuit. These are the circles moving along the circuit when the switch is closed. They are pushed to move by a FORCE present inside the battery which we call VOLTAGE. So VOLTAGE is the FORCE and when this ELECTRIC FORCE is applied to the circuit, electrons move (flow) a distance. Now, remember that WORK = FORCE x DISTANCE; the electrons move around the circuit (a distance) because of the electric force: voltage. Now, POWER (in WATTS) is just how fast it happens = WORK / TIME. 3. Find the size buttons on the right and click small so you can fit more on the screen. 4. Leaving the first circuit you made on the screen, build a SECOND CIRCUIT on this screen that looks like the one right. It s very similar to the other one except that it has TWO batteries connected in SERIES. PUT THE BATTERIES IN AS SHOWN!!!! 5. Close the switch on both circuits and observe the light bulb brightness AND the electron flow. Question 1: What do you observe that is happening differently between them?

2 6. Measuring the VOLTAGE (force): Now click the button on the right to get the Voltmeter. 7. Drag the voltmeter probes so that you can measure the voltage on the light bulb as shown here: If you don t get a reading, move the probes around so they accurately touch the light bulb connections. What voltage do you read for the circuit with one battery? One battery circuit voltage: 8. Now measure the voltage in the second circuit having two batteries in SERIES. Two batteries in SERIES circuit voltage: Question 2: How did the battery voltage change from one circuit to the other? Question 3: Which circuit has more POWER? Explain your answer using the words LIGHT BULB BRIGHTNESS, ELECTRON FLOW and VOLTAGE. PREDICT: Make predictions about another circuit that will have THREE BATTERIES IN SERIES? Use the terms: LIGHT BULB BRIGHTNESS, ELECTRON FLOW and VOLTAGE in your prediction. 9. Build the THIRD CIRCUIT like the one shown right to test your prediction. PUT THE BATTERIES IN AS SHOWN!!!!! Use the voltmeter to get the voltage reading at the bulb. Three batteries in SERIES circuit voltage: Question 4: How does this circuit work different than the other two? Was your prediction correct?

3 IF YOUR WORK FROM PART ONE IS STILL PRESENT, CLEAR THE SCREEN USING THE Clear BUTTON BEFORE YOU BEGIN PART 2: THE PARALLEL ELECTRIC CIRCUIT Procedure: 1. Build the circuit as shown here. NOTE the TWO WIRES. Use this basic plan for the other circuits you build for the rest of this activity adding batteries and wires where needed. PUT THE BATTERY IN AS SHOWN!!!! 2. Close the switch and use the voltmeter to measure the voltage at the bulb. One battery circuit voltage: 3. Find the size buttons on the right and click small so you can fit more on the screen. 4. Build a SECOND CIRCUIT on this screen that looks like the one right that has two batteries in PARALLEL. PUT THE BATTERIES IN AS SHOWN!!!!! 5. Close the switch on both circuits and observe the light bulb brightness AND the electron flow. 6. Measure the voltage on the bulb for this second circuit having two batteries in PARALLEL. Two batteries in PARALLEL circuit voltage: Question 1: What do you observe that is happening different between them? (Observe batteries closely) PREDICT: Make predictions about another circuit that will have THREE BATTERIES IN PARALLEL? Use the terms: LIGHT BULB BRIGHTNESS, ELECTRON FLOW and VOLTAGE in your prediction. (OVER)

4 7. Build the THIRD CIRCUIT like the one shown to test your prediction. Use the voltmeter to get the voltage reading at the bulb. Three batteries in PARALLEL circuit voltage: Question 2: How does this circuit work different than the other two? (again observe batteries closely) Was your prediction correct? PART 3 / CONCLUSION How is the voltage in a circuit affected by batteries connected in SERIES? How is the voltage in a circuit affected by batteries connected in PARALLEL? TRY TO ANSWER THIS EXTENSION QUESTION IF YOU CAN What benefit does connecting batteries in PARALLEL have for any circuit like perhaps a radio?

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