Name Date Class The Effect of an Electric Field on Moving Charges Lab 29: The Effect of an Electric Field on Moving Charges Problem To investigate the effect of a static electric field on various moving charges Background As scientists first began investigating the properties of atoms, they discovered that they could extract negatively charged particles. They called these particles electrons. In order to understand the nature of these particles, scientists wanted to know how much charge they carried and how much they weighed. J.J. Thomson was a physics professor at the famous Cavendish Laboratory at Cambridge University. In 1897, Thomson showed that if you could measure how far a beam of electrons was bent in an electric field and in a magnetic field, you could determine the charge-to-mass ratio (q/me) for the electrons. Knowing this ratio, the individual charge and mass of an electron could be calculated. Another particle ejected during nuclear decay is the alpha particle. An alpha particle is a helium nucleus, that is, a helium atom without its two electrons. As you will see, a beam of alpha particles can also be deflected by an electric field. Skills Focus Predicting, observing, drawing conclusions Procedure 1. Start Virtual Physics and select Effect of an Electric Field on Moving Charges from the list of assignments. The lab will open in the Quantum laboratory. 2. The experiment will be set up on the table. There is an electron gun on the left side of the as the source. What type of charge do electrons have? 3. There is a phosphor screen on the right side of the table to detect the charged particles. Turn on the phosphor screen by clicking on the green/red button. What do you observe and what do you think that it shows? The Effect of an Electric Field on Moving Charges Virtual Physics Lab Workbook, by Brian F. Woodfield, Steven Haderlie, Heather J. McKnight, and Bradley D. Moser. Published by Pearson Learning Solutions. Copyright © 2008 by Pearson Education, Inc. ISBN 1-269-73240-4 92 Name Date Class The Effect of an Electric Field on Moving Charges 4. Drag the lab window down and left and the phosphor screen window up and right in order to minimize the overlap. Push the Grid button on the phosphor screen. Click once above the ones place on the Electric Field modifier meter near the center of the table. Observe the spot. Click a few more times above the ones place on the Electric Field, until the field is at 5V. (If you mistakenly click between digits, it will move the decimal point. To move the decimal point back again, click where it was originally.) What happens to the spot from the electron gun on the phosphor screen? 5. Predicting What do you think would happen to the spot if you increased the voltage of the electrons leaving the electron gun? Why? 6. Observing Increase the voltage of the source by clicking above the hundreds place on the electron gun voltage controller (the second meter from the left). You are not changing the number of electrons leaving the gun, just giving each of them greater electrical potential energy. What happens to the spot on the phosphor screen? Why does this happen? 7. Predicting What do you think would happen to the spot now if you increased the voltage on the Electric Field modifier that the electron beam is passing through? Why? 8. Test your prediction, then zero out the Electric Field meter by clicking on the appropriate digit buttons until the spot on the phosphor screen is once again centered. ISBN 1-269-73240-4 9. Double-click or click and drag the electron gun to move it to the Stockroom counter. Enter the Stockroom by clicking inside it. Double-click the electron gun to move it back to the shelf. Double-click on the alpha source to select it and move it to the Stockroom counter. Click on the green Return to Lab arrow to return to the lab. Drag the alpha source from the Stockroom counter and place it on the table where the electron gun was originally placed (the middle spotlight). Click on the front of the alpha source to open the shutter. What appears on the phosphor screen? What charge do alpha particles have? The Effect of an Electric Field on Moving Charges 93 Virtual Physics Lab Workbook, by Brian F. Woodfield, Steven Haderlie, Heather J. McKnight, and Bradley D. Moser. Published by Pearson Learning Solutions. Copyright © 2008 by Pearson Education, Inc. The Effect of an Electric Field on Moving Charges Name Date Class 10. Change the unit for the Electric Field from V (volts) to kV (kilovolts) by clicking once above the unit. This electric field is one thousand times stronger than what you used previously for the electron gun. Observe the spot as you increase the Electric Field strength from 0 kV to 5 kV. The movement is slight so pay careful attention. Which direction did the spot move when you increased the electric field? How does this direction of movement compare with the direction of movement for the electron beam in the electric field? 11. Drawing Conclusions Why do you think that it takes a significantly stronger electric field strength to move the beam of alpha particles compared to the beam of electrons? The Effect of an Electric Field on Moving Charges Virtual Physics Lab Workbook, by Brian F. Woodfield, Steven Haderlie, Heather J. McKnight, and Bradley D. Moser. Published by Pearson Learning Solutions. Copyright © 2008 by Pearson Education, Inc. ISBN 1-269-73240-4 94 Name Date Class Lab 32: Series and Parallel Circuits Purpose To build series and parallel circuits and study the differences between them Background Electricians are called upon whenever new buildings need electrical work. The electrician surveys the site and determines what kind of currents and voltages are required to satisfy the client’s needs. Sometimes the circuit requires components to be connected like you would in plumbing so the water could flow. This is called a series circuit. Sometimes the components need to be connected in parallel, like the rungs on a ladder. Each type of circuit has its advantages. In this lab, you will study the advantages of and the differences between series and parallel circuits. Skills Focus Classifying, inferring, comparing and contrasting, drawing conclusions Procedure 1. Start Virtual Physics and select Series and Parallel Circuits from the list of assignments. The lab will open in the Circuits laboratory. Series and Parallel Circuits 3. You need to build a circuit that has only one path for the current to follow. This is called a series circuit. Use only resistors to make this circuit. On the engineering paper, place five resistors in series using the resistor symbol at the top. First start by connecting the first resistor to an open end of the function generator. Then drag out a new resistor and place it next to the open end of the last placed resistor. Follow the same process until you have five resistors in series. Complete the circuit by connecting the last resistor you added to the other side of the voltage source. 4. Make sure that that there is only one path for the current to flow through the resistors you connected in Step 3. After you have placed the resistors on the circuit, you will need to change the resistance of each of the resistors as specified in Step 5. You can do this by clicking on the number next to the resistor. A small box will pop up where you can adjust the value of the resistor. 102 Series and Parallel Circuits Virtual Physics Lab Workbook, by Brian F. Woodfield, Steven Haderlie, Heather J. McKnight, and Bradley D. Moser. Published by Pearson Learning Solutions. Copyright © 2008 by Pearson Education, Inc. ISBN 1-269-73240-4 Series and Parallel Circuits 2. The laboratory will be set up with a function generator set to 12 V DC already on the engineering paper, which is the schematic or plan of the circuit built on the breadboard. In this assignment, you will have to add resistors to create a circuit. To add resistors, simply click on the resistor symbol at the top of the engineering paper and drag it onto the paper. You may move resistors around by clicking them on the middle blue dot. You can also extend their leads by clicking on the end red dots and dragging them to where you want to connect them to other components. The line will be green if it is in an allowable location. You will notice that the breadboard will automatically populate with the resistors that you add to the schematic. Name Date Class 5. Change the value of each resistor to the match the values found in Data Table 1. Assume that resistor 1 is the one connected to the positive side of the voltage source and resistor 5 is the one connected to the negative side of the voltage source. Data Table 1 Resistor Number Resistor Value ( 1 120 2 500 3 200 4 135 5 10,000 ) 6. Using the multimeter to measure the current and the voltages across each resistor. The symbol for the multimeter has a DMM in the middle of it. Click and drag the red lead to one side of the resistor. It should lock into place. Then click and drag the black lead to the other side of that same resistor to measure the drop in voltage across the resistor. You can read the voltage and current from the yellow multimeter display. To measure the current passing through the resistor, change the multimeter from VDC to IDC, which changes the variable being measured from voltage to current. Record your measurements in Data Table 2. NOTE: For the ammeter to measure current, it should be placed with both leads on one side of the resistor. This is because the current must flow through the ammeter to measure it. However, the voltmeter needs to compare voltages at two points, so it should be hooked up across the resistor. Data Table 2 Resistor Number Voltage (V) Current (A) 1 2 3 4 5 Circuits Parallel andand Series Series Parallel Circuits ISBN 1-269-73240-4 7. Now, using the same resistors as before, you will build a parallel circuit. This is done by creating multiple paths for the current to follow. To do this, first move all the resistors to the bottom half of the paper, but don’t delete them. Series and Parallel Circuits 103 Virtual Physics Lab Workbook, by Brian F. Woodfield, Steven Haderlie, Heather J. McKnight, and Bradley D. Moser. Published by Pearson Learning Solutions. Copyright © 2008 by Pearson Education, Inc. Name Date Class 8. First add a new resistor in series to the beginning of the function generator. Change its resistance to equal 1 . 9. Drag and set the other five resistors back onto the lines so that the circuit looks like a ladder with the resistors as the steps. Your final schematic should look like the picture on the right. 10. Using the same technique as Step 6, measure the voltage and current across each of the five resistors listed in Data Table 1. Remember that it is a DC source, so you must use the DC Voltmeter and DC Ammeter. Record your results in Data Table 3 below. Data Table 3 Resistor Number Voltage (V) Current (A) 1 2 3 4 5 Analyze and Conclude 1. Classifying 2. Inferring circuit? What are the variables in this experiment? Which variables stay the same, and which change in the series 3. Which variables stay the same, and which change in the parallel circuit? How do parallel and series circuits differ? Series and Parallel Circuits 104 Series and Parallel Circuits Virtual Physics Lab Workbook, by Brian F. Woodfield, Steven Haderlie, Heather J. McKnight, and Bradley D. Moser. Published by Pearson Learning Solutions. Copyright © 2008 by Pearson Education, Inc. ISBN 1-269-73240-4 Series and Parallel Circuits 4. Comparing and Contrasting Name Date Class 5. Drawing Conclusions In what way does a series circuit look like it would have the same current throughout? 6. In what way would your answer to question 4 above be important for an electrician to know? Going Further 105 Virtual Physics Lab Workbook, by Brian F. Woodfield, Steven Haderlie, Heather J. McKnight, and Bradley D. Moser. Published by Pearson Learning Solutions. Copyright © 2008 by Pearson Education, Inc. Series and Parallel Circuits Series and Parallel Circuits Series and Parallel Circuits ISBN 1-269-73240-4 7. Now go back to the circuits and replace the resistors with light bulbs. The symbol for a light bulb is a white circle with an X in the middle. Place them on the engineering paper. Create a series circuit and a parallel circuit like the ones you made earlier. Then try removing one of the light bulbs. Record below what happens in each case. Also, record the relative brightnesses of the bulbs in each circuit. Name Date Class Lab 33: The Effect of a Magnetic Field on Moving Charges Problem To investigate the effect of a magnetic field on moving charges Background Charged particles at rest are not affected by static magnetic fields. However, when such charged particles are in motion, they are deflected by magnetic fields. The discovery that flowing electrons are affected by magnets was a pivotal discovery at the turn of the 20th century. Today, many common technological applications, from electric motors to television screens, make use of this interaction. In cathode ray television tubes, for example, magnets are used to move a stream of electrons. As the electrons hit the screen, the screen glows momentarily where it was hit. Similarly, Earth’s magnetic field deflects charged particles from the sun. In this lab, you will study the effect of a magnetic field on different types of charged particles. Skills Focus Predicting, observing, developing hypotheses, drawing conclusions, applying concepts Procedure 1. Start Virtual Physics and select Effect of a Magnetic Field on Moving Charges from the list of assignments. The lab will open in the Quantum laboratory. 2. The experiment will be set up on the table. An electron gun on the left side of the table serves as the source of electrons. What type of charge do electrons have? 3. There is a phosphor screen on the right side of the table to detect charged particles. Turn on the phosphor screen by clicking on the green/red button. What do you observe? What do you think that it shows? The Effect of a Magnetic Field on Moving Charges Virtual Physics Lab Workbook, by Brian F. Woodfield, Steven Haderlie, Heather J. McKnight, and Bradley D. Moser. Published by Prentice Hall. Copyright © 2008 by Pearson Education, Inc. ISBN 0-558-83901-0 106 Name Date Class 4. Drag the lab window down and to the left and the phosphor screen window up and to the right in order to minimize the overlap between the two. Then push the Grid button on the phosphor screen. Set the Magnetic Field to 30 μT (microtesla) on the magnetic meter near the phosphor screen by clicking the button above the tens place three times. (If you mistakenly click between the digits, it will move the decimal point. To move the decimal point back again, click where it was originally.) What happens to the spot from the electron gun on the phosphor screen? 5. Predicting What do you think would happen to the spot if you increased the voltage of the electrons leaving the electron gun? Why? 6. Observing Increase the voltage of the source by clicking above the hundreds place on the electron gun voltage controller (the second meter from the left). This does not change the number of electrons leaving the gun. Rather, it just gives each electron more electrical potential energy. What happens to the spot on the phosphor screen when the voltage is increased? Why does this happen? 7. Predicting What do you think would happen to the spot now if you increased the strength of the magnetic field that the electron beam is passing through? Why? 8. Test your prediction, then zero out the Magnetic Field meter by clicking on the appropriate digit buttons until the spot on the phosphor screen is centered once again. ISBN 0-558-83901-0 9. Double-click or click and drag the electron gun to move it to the Stockroom counter. Enter the Stockroom by clicking inside it. Double-click the electron gun to move it back to the shelf. Double-click on the alpha source to select it and move it to the Stockroom counter. Click on the green Return to Lab arrow to return to the lab. Drag the alpha source from the Stockroom counter and place it on the table where the electron gun was originally placed (the middle spotlight). Click on the front of the alpha source to open the shutter. What appears on the phosphor screen? What charge do alpha particles have? The Effect of a Magnetic Field on Moving Charges Virtual Physics Lab Workbook, by Brian F. Woodfield, Steven Haderlie, Heather J. McKnight, and Bradley D. Moser. Published by Prentice Hall. Copyright © 2008 by Pearson Education, Inc. 107 Name Date Class 10. Change the unit for the Magnetic Field from μT to mT (millitesla) by clicking once above the unit. Click above the hundreds place three times to set the Magnetic Field to 300 mT. This magnetic field is 10,000 times stronger than the one you used for the electron gun. Which direction did the spot move when you increased the magnetic field? How does this direction of movement compare with the direction of movement for the electron beam in the magnetic field? 11. Developing Hypotheses A charged particle at rest wouldn’t be affected by a magnetic field at all, so why are moving charged particles affected? 12. Drawing Conclusions Why do you think it takes a significantly stronger magnetic field strength to move the beam of alpha particles compared with the beam of electrons? 13. Applying Concepts What technologies or applications of the connection between electricity and magnetism can you think of? Describe the physical processes. The Effect of a Magnetic Field on Moving Charges Virtual Physics Lab Workbook, by Brian F. Woodfield, Steven Haderlie, Heather J. McKnight, and Bradley D. Moser. Published by Prentice Hall. Copyright © 2008 by Pearson Education, Inc. ISBN 0-558-83901-0 108
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