Lab 8_FaradaysLaws_updated

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University of North Carolina, Chapel Hill *

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2102

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Apr 3, 2024

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PHYS 2102 Lab Spring 2023 Summer Lab PHYS 2 LAb Lab 08: Magnetic Field and Faraday’s Law You will need to run a simulation to do the lab. Answer the following questions as you work through the lab. Write your answers in blue . (Note that we may miss your response if it does not stand out) Re-load the file in Word or PDF format in Canvas before the due date. Objective In this lab, you will (i) Investigate the properties of magnet and (ii) U se Faraday’s Law to predict the properties of induced emf in a coil. You will investigate the induced emf generated by a moving bar magnet and coil. You will: ● Move a bar magnet near one or two coils to make a light bulb light-up. ● View the magnetic-field lines. ● Use an Ammeter (current meter) to show the direction and magnitude of the induced current. ● View the magnetic field-lines. ● Observe how the compass needle deflection and the electron movement inside the coil change by changing the source of an electromagnet from DC to AC. Theory: In the previous lab, we did an experiment to show how the current flowing through a wire produces a magnetic field around it. In this lab, we will study how the changing magnetic fields produce electric fields, a phenomenon known as ‘ Magnetic Induction ’. Faraday’s Law: According to Faraday's Law of Induction, a changing magnetic flux, Ф , through a coil induces an EMF ( electromotive force -- a voltage ) given by: 𝜀 = −𝑁 𝛥𝛷 𝛥? ………. (1)

PHYS 2102 Lab Spring 2023 Summer Lab PHYS 2 LAb where 𝛷 = ? ⃗ . ? is the magnetic flux due to a magnetic field ( ? ⃗ ) passing through the cross-sectional area (A) of the loop of a wire, ? is a vector perpendicular to the area of the loop. N is the number of turns (loops) of the wire in the coil. For this experiment, the area of the coil remains constant and as the coil passes into or out of the magnetic field, hence Eq. 1 can be re-written as; 𝜀 = −𝑁? 𝛥? 𝛥? … ……. (2) Lenz's law states that the current induced in a circuit (loop) due to a change in a magnetic field is directed to oppose the change in flux and to exert a mechanical force which opposes the motion. Simulation: Open Faraday’s Electromagnetic Lab https://phet.colorado.edu/sims/cheerpj/faraday/latest/faraday.html?simulati on=faraday Please take a few minutes to become familiar with different tabs and select options present in the simulation. 1. Bar Magnet 1. Click on the ‘Bar Magnet’ Tab you should see a bar magnet and a compass on the screen. You should note that the color red refers to North- and white refers to South-poles of the magnetic. Place the compass at the North end of the bar magnet and observe which way the “red tip” of the compass points. Move the compass to the South end, and observe where the “red tip” of the compass points. Based on your observation, describe how the compass works: [2 Points] The red tip of the compass compass points south 2. Use your response above to explain why the geographic North-pole is the magnetic South-pole. [2 Points] Because if we think of earth as a magnet then the north pole is where the southern magnetic field is the strongest.

PHYS 2102 Lab Spring 2023 Summer Lab PHYS 2 LAb 3 . Check the “ show field ” box if it is not already checked. This shows how the compass needle would orient itself at each point around the bar magnet. Joining these in the direction of the red arrow gives essentially the field line diagram of the bar magnet. Sketch a diagram of these using PowerPoint/Paint (some drawing tool) and paste your sketch below. Use arrows to represent the direction in which the red tip (N-pole) points. Make sure you label the poles of the magnets properly. [You need this diagram for (5). Do not delete it yet!] [4 Points]

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PHYS 2102 Lab Spring 2023 Summer Lab PHYS 2 LAb

PHYS 2102 Lab Spring 2023 Summer Lab PHYS 2 LAb 4. Place the compass next to the North-Pole of the bar magnet and press the Flip Polarity button. What happens to the magnet and the compass? [1 Point] The north and south pole flipped and the compass needle did a 180 5. Click ‘See Inside Magnet’. What do you see? Add this to your diagram above. Drawn in (2) above and paste it below. [3 Points] You see the magnet force in the magnetic going from north to south 6. Click ‘Show Field Meter’ and move the meter around outside the magnet and answer the following questions: [6 Points] Where is/are ?𝑎??𝑖???? ?? ? maximum? What is/are the value/s there? For me the most I got was 103.32 which was off the south pole but I got very close on the north pole side getting 102.78 Where is/are ?𝑎??𝑖???? ?? ?? maximum? What is/are the value/s there? Again at the pole where I got the value 102.63 for the south pole and the value 102.48 for the north pole it was also negative if u were above or below the magnet Where is/are ?𝑎??𝑖???? ?? ?? maximum? What is/are the value/s there? The highest values I got were below the south pole 100.25 or above the north pole 100.21 Magnetic Field Vector : Sketch the bar magnet using PowerPoint/Paint (or some drawing tool) and show the regions where [4 Points] a) B x is positive and negative [Note the angle specified in the B-Field meter]. b) B y is positive and negative

PHYS 2102 Lab Spring 2023 Summer Lab PHYS 2 LAb Red area = bx positive blue area = bx negative

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PHYS 2102 Lab Spring 2023 Summer Lab PHYS 2 LAb Yellow dots = by positive green dots = by negative Place the B-Field meter at a location to the left and underneath the bar magnet . Take a screenshot and paste below. What are the Bx, By and ? ⃗ values ? Verify the mathematical relationship between the three. Also note the value of angle Θ . What is the mathematical relationship between B x and B y and angle Θ? Verify this for the values noted. Show your calculation in order to get full credit. [4 Points]

PHYS 2102 Lab Spring 2023 Summer Lab PHYS 2 LAb

PHYS 2102 Lab Spring 2023 Summer Lab PHYS 2 LAb B = sqrt((-7.9^2)+(12.74^2)) = 14.9905 Tan^-1(by/bx) = theta Tan^-1(12.74/-7.9) = -58.197 90-121.8 = -31.8 -31 -58.197 = -90

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PHYS 2102 Lab Spring 2023 Summer Lab PHYS 2 LAb 2: Electromagnet – Is Electromagnetism Reversible? 1. Choose the Electromagnet Tab . You should see a battery attached to a loop of coil (an electromagnet) and a compass on the screen. Make sure the current source is set to DC and uncheck the “show field” box. Set the number of loops to 4. Move the compass around the electromagnet and describe what it does: [2 Points] The red side point at the side of the coil closer to the tail of the battery while it is repelled from the a coil at the head of the battery 2. Move the compass around the electromagnet in order to determine the North and South poles. Draw a picture of the electromagnet coil and label the ends as either North or South Pole. (No need to make it complicated, just label them properly). On your diagram indicate the direction of current flow in the coil (Note: the simulation shows the flow of electrons. How does this flow relate to the direction of conventional current?) [3 Points]

PHYS 2102 Lab Spring 2023 Summer Lab PHYS 2 LAb

PHYS 2102 Lab Spring 2023 Summer Lab PHYS 2 LAb 3. Now check the “ show field ” box and observe the magnetic field lines. How does the magnetic field of the electromagnet compare to that of the bar magnet? Add the field lines to your diagram above. [2 Points] The magnetic field is more curved than a bar magnet

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PHYS 2102 Lab Spring 2023 Summer Lab PHYS 2 LAb

PHYS 2102 Lab Spring 2023 Summer Lab PHYS 2 LAb 5. Change your current source from DC to AC and describe what the compass does? [2 Points] It flips back and forth like the current 6. Observe the electrons in the AC current source and compare their movement to those in the DC current source. Explain the difference between DC and AC in terms of electron movement. [2 Points] In dc the electrons move in one direction so the magnetic field is constant while in ac it alternates so the electron move in the opposite direction leading to the reversal of the magnetic field 7. Change back to DC source. Use the field-meter to observe the field at various spots. Where is the ? strongest and where is it weakest? [2 Points] Stongest to the immediate left or right of the coils and is weakest above the battery 8. Place the field meter near one of the ends of the coil (set the number of loops to 1). Write down the value of B . Start increasing the number of loops and record corresponding value of B . [2 Points] No. of Loops ? 𝑉𝑎??? (𝐺) 1 75 2 150 3 225 4 300 Perform a linear fit of this data using Excel and paste the graph below. Make sure the equation of linear fit is displayed. [5 Points]

PHYS 2102 Lab Spring 2023 Summer Lab PHYS 2 LAb [Helpful Video: https://www.youtube.com/watch?v=L_a8Z0BVjyM ] Based on the graph explain whether linear fit is an appropriate choice to describe the relationship between ? and Number of Turns of the coil? [1 Point] yes

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PHYS 2102 Lab Spring 2023 Summer Lab PHYS 2 LAb 3: Pickup Coil 1. Choose the ‘ Pickup Coil ’ tab. Set the number of loops to “1” and loop area 50%. Write your observations of the light bulb when [4 Points] a) the magnet is not moving and is not inside the loop. off b) the magnet is moving and is not inside the loop. Flickers occasinally c) the magnet is not moving and is inside the loop. off d) the magnet is moving and is inside the loop. Flickers at different intesities 2. If you change the speed of the magnet, does it affect your results? If so, how? [2 Points] Faster the magnet moves the greater the intesnity 3. If you change the strength of the magnet, does it affect your results? If so, how? [3 Pts.] Yes it also increases the light intensity 4. Increase the number of loops to “3” and note how it affects your results. [2 Points] Increases intesity 5. Increase the loop area to “100” and note how it affects your results. [2 Points] Increases intensity again 6. Replace the bulb with the voltage indicator . Observe what happens to the voltage induced as you change [4 Points] a. the speed of the magnet: More voltage change the faster the magnet goes b. the strength of the magnet: more voltage change the stronger the magnet c. number of loops to 3: change in voltage increases when loops is increased d. increases the loop area to 100: Voltage increases again 7. What is the sign of the induced voltage as the North -pole end of the magnet moves towards the coil. [1 Point]

PHYS 2102 Lab Spring 2023 Summer Lab PHYS 2 LAb Sign negative 16. As the magnet passes through the coil and the South-pole end recedes away from the coil, what is the sign of the induced voltage? [1 Point] positive 17. Relate these two findings to Lenz’s law. [3 Points] Lenz's law describes the direction of the induced current in a circuit resulting from a change in magnetic field. The law states that the direction of the induced current is opposite to the change in magnetic flux, which in turn creates a force that opposes the motion. Specifically, when a magnet's north pole approaches a coil, the resulting increase in magnetic flux induces a current with a negative sign. Conversely, when the magnet's south pole recedes from the coil, the decrease in magnetic flux induces a current with a positive sign. 4: Transformer 1. Why doesn’t the transformer work with DC voltage? (Hint: Faraday’s law). [2 Points] Faraday's law states that a changing magnetic flux through a coil induces an emf. In the case of using a DC voltage, the current may be constant, but if there is a change in the magnetic field, there will be an induced EMF. However, if the magnetic field is constant and not changing, then no EMF will be produced to affect the transformer. 2. Switch the current source to AC. What five things can you adjust to get the highest maximum voltage? [3 Points] High frequency Shell form design Increase capacity Laminating the core Reucing the magnetized effect 5: Generator 1. What does RPM (written in the wheel) stand for? [1 Point] Revolution per minute

PHYS 2102 Lab Spring 2023 Summer Lab PHYS 2 LAb 2. Open the Tap. What four things can you adjust to get the highest maximum voltage? [2 Points] Increasing the are of the coil Increasing num of coils Increasing rpm Increasing strength of magnetic coil 3. In previous labs the magnet was moved in-out (or towards/away) from the coil for the bulb to glow. However, in this case the magnet is rotating but the bulb is still glowing. Explain how is this possible. (Hint: Think about Flux! Faraday’s law). [3 Points] Faraday's law states that a changing magnetic flux induces EMF in a coil. A moving magnet causes a change in the magnetic field and hence the magnetic flux, which creates EMF. The bulb remains lit as long as the magnet rotates and induces the EMF.

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Lab 8_FaradaysLaws_updated

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