UC Davis Electricity and Magnetism

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ybqnln

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University of California Davis

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Two versions of answers for this lab

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LAB 12: L R CIRCUITS NAME_____________________________________ PLEDGE______________ Please go to the following webpage - https://phet.colorado.edu/en/simulation/legacy/circuit-construction-kit-ac Run the application and set up the following circuit. Typically, and inductor is usually a coil of wire wrapped around a piece of iron. Yes, it’s an electromagnet that we do not use for picking stuff up! 1) By right clicking on the inductor, set it to 10 Henries (No, that really is the unit) 2) Ensure that both bulbs are 10 ohms 3) Close the switch. Describe your observations. 4) Describe in your own words what effect the inductor has on the current. 5) Now open the switch. Again, describe your observations. 6) Why do you think a current was able to flow after we effectively removed the battery from the circuit? A couple of things to consider. When the current through an inductor changes, Lenz’s law gives us a clue as to how the inductor will act. a) The inductor will generate an EMF which opposes the change taking place. b) The size of the EMF will be proportional to the rate of change of current (Why?) c) The constant of proportionality depends on the geometry of the coils and is called the inductance L, measured in Henries 𝜀 = −𝐿 𝑑𝐼 𝑑𝑡 Consider the loop in the diagram above. We can use Kirchoff 2 (loop) to write a differential equation for current I If ε is the emf of the battery and -𝐿 𝑑𝐼 𝑑𝑡 is the emf generated in the coil, the sum of these two should equal the p.d across the resistor, IR. Write down and solve the differential equation, assuming I = 0 when t = 0 Now consider what happens to the bottom loop when we open the switch. There is now only one source of EMF. Write down and solve a differential equation in 𝐼 for this case, assuming that the current at 𝑡 = 0, when the switch was opened, was 𝐼0
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Explanation & Answer:

6 Questions

Tags: differential equation rate of change Electricity and Magnetism battery circuit geometry of the coils

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Explanation & Answer

View attached explanation and answer. Let me know if you have any questions.First version done!

VIRTUAL INVESTIGATION INTO THE BEHAVIOR OF L R CIRCUITS
NAME_____________________________________

PLEDGE______________

Please go to the following webpage - https://phet.colorado.edu/en/simulation/legacy/circuit-construction-kit-ac
Run the application and set up the following circuit.

Typically, and inductor is usually a coil of wire wrapped around a piece of iron. Yes, it’s an electromagnet that we do
not use for picking stuff up!
1) By right clicking on the inductor, set it to 10 Henries (No, that really is the unit)
2) Ensure that both bulbs are 10 ohms
3) Close the switch. Describe your observations.
The bulb on the bottom immediately lit up, while the bulb next to the inductor gradually lit up.

4) Describe in your own words what effect the inductor has on the current.
The inductor reduces current flow for a gradual amount of time. As the resistance in the inductor decreases,
the current passing through the inductor starts to increase.

5) Now open the switch. Again, describe your observations.

The two bulbs dimmed at the same time but not immediately.

6) Why do you think a current was able to flow after we effectively removed the battery from the circuit?
The current was still able to flow because the inductor was able to continue to power the circuit because it
creates a magnetic field with its stored energy.

A couple of things to consider. When the current through an inductor changes, Lenz’s law gives us a clue as to
how the inductor will act.
a) The inductor will generate an EMF which opposes the change taking place.
b) The size of the EMF will be proportional to the rate of change of current (Why?)
c) The constant of proportionality depends on the geometry of the coils and is called the inductance L,
measured in Henries

𝜀 ...