**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

**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.

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