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Inductor Questions and Answers

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Inductor Questions

These questions are related to Capacitor Circuit, Capacitor Connections, Capacitive Reactance, and RC Circuit Time Constant which are covered in detail here:

Inductors in Series | Inductors in Parallel

Inductive Reactance

RL Circuit Time Constant

 

1. Inductance is defined as what?
Inductance is the ability of a component to oppose any change in (increase or decrease) in the current.

2. Name the base unit used when measuring inductance.
Henry (H)

3. State the relationship between the inductance value of a coil and the amount of emf it produces.
The greater inductance value or the faster the rate of change of current, the greater the emf induced in the circuit.
\[{{V}_{L}}=L\frac{di}{dt}\]

4. What effect (increase or decrease) would the following changes have on the inductance of a coil?
a. Increase in the number of turns of wire. Increase
b. Removal of its iron core. Decrease
c. Spacing the turns of wire farther apart. Decrease

5. For a coil that has an inductance of 5H and a DC resistance of 10 Ω:
a. Calculate the RL time constant.
\[\tau =\frac{L}{R}=\frac{5}{10}=0.5\operatorname{seconds}\]
b. When the DC voltage is applied to this coil, approximately how long will it take for the current to reach its maximum value?
Five-time constants.

6. Define the term inductive reactance.
The opposition to AC current flow is called inductive reactance.
${{X}_{L}}=2\pi fL$

7. What is the base unit used to measure inductive reactance?
Inductive reactance is measured in ohms Ω.

8. State whether the inductive reactance (increases or decrease) with each of the following changes:
a. Increase in the frequency of the AC supply source. Increase.
b. Decrease in the inductance of the coil. Decrease.
The above results are based on the following formula:

${{X}_{L}}=2\pi fL$

9. Calculate the inductive reactance of a 2.5 H inductor when operated at a frequency of 50 Hz.
\[{{X}_{L}}=\text{ }2\pi fL;\text{ }2\pi *50*2.5\text{ }=\text{ }785.39\Omega \]

10. A 6 H inductor is connected to a 12 VDC source. What is the value of its inductive reactance? Explain.
An inductor in a DC circuit has no inductive reactance according to the following formula:

${{X}_{L}}=2\pi fL=2\pi *0*6=0\Omega $

11. An AC voltage of 240 volts with a frequency 60 Hz is applied to a 0.5 H inductor. Neglecting its small amount or wire resistance, how much current would flow through it?

\[\begin{align}  & {{X}_{L}}=2\pi fL=2\pi *60*0.5=\text{ }188.5\Omega \Omega  \\ & I\text{ }=\frac{{{V}_{s}}}{{{X}_{L}}}=\frac{240}{188.5}=1.27A \\\end{align}\]

12. Determine the total inductance of a 6 H and a 4 H inductor connected in:
a. Series.
\[{{L}_{T}}={{L}_{1}}+{{L}_{2}}=\text{ }6+4=10H\]
b. Parallel.
\[{{L}_{T}}=\frac{{{L}_{1}}*{{L}_{2}}}{{{L}_{1}}+{{L}_{2}}}=\frac{4*6}{4+6}=2.4H\]

13. Inductors of 1H and 2H are connected in series to a 440V, 60Hz power supply.
a. Determine the total current flow for the circuit.

$\begin{align}  & {{X}_{T}}=2\pi f{{L}_{T}}=2\pi *60*3=1131\Omega  \\ & I=\frac{{{V}_{s}}}{{{X}_{T}}}=\frac{440}{1131}=0.389A \\\end{align}$
b. Repeat for the two inductors connected in parallel to the power supply.

$\begin{align}  & {{X}_{T}}=2\pi f{{L}_{T}}=2\pi *60*\left( \frac{1*2}{1+2} \right)=251.33\Omega  \\ & I=\frac{{{V}_{s}}}{{{X}_{T}}}=\frac{440}{251.33}=1.75A \\\end{align}$

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About Ahmad Faizan

Mr. Ahmed Faizan Sheikh, M.Sc. (USA), Research Fellow (USA), a member of IEEE & CIGRE, is a Fulbright Alumnus and earned his Master’s Degree in Electrical and Power Engineering from Kansas State University, USA.