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LR Derivations

Rise and Decay

LR DerivationsRise and Decay

Derivations

Use the formulas below to drive the following equations.
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Ohm's Law

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Back EMF

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Time Constant

Rise of Current

Solve for the Rise of Current as a function of time, i(t)
HINT - See below.

Step 1 - Draw an LR Circuit.

Your circuit should have a double throw single pole switch so the circuit can be flipped between rise and decay of current.

Step 2 - Flip the Switch to Rise of Current and Apply the Loop Rule

Rise of Current is when the switch is in position "a".

Step 3 - Separation of Variables

Step 4 - Integrate

Step 5 - Solve for i(t)

Decay of Current

Solve for the Decay of Current as a function of time, i(t)

HINT - Use i = -dq/dt

Step 1 - Draw an LR Circuit

Your circuit should have a double throw single pole switch so the circuit can be flipped between rise and decay of current.

Step 2 - Flip the Switch to Decay of Current and Apply the Loop Rule

Decay of Current is when the switch is in position "b".

Remember the HINT

Step 3 - Separation of Varialbles

Step 4 - Integrate

Step 5 - Solve for i(t)

Graphs and Equations

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Graph A

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Graph B

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Graph C

Match the graph to the description below.

Rise of Current

1. Current in the Circuit

2. Voltage across the Resistor

3. Voltage across the Inductor


Decay of Current

4. Current in the Circuit

5. Voltage across the Resistor

6. Voltage across the Inductor

David Carroll - Plano West
www.GravityKills.net
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