Everything Science Grade 12

CHAPTER 13. ELECTRODYNAMICS 13.4

L =

μ 0 AN^2

l

=

4 π× 10 −^7 × 0 , 0022 × π× 20002

0 , 05

= 0,00126 H

= 1,26 mH

An inductor in an AC circuit also has a reactance, XL. Reactance is the property of an
inductor that opposes the flow of AC current. Reactance is defined by:

XL= 2πfL

where L is the inductance and f is the frequency of theAC.

If we examine the equation for the reactance of an inductor, we see that inductive
reactance increases withincreasing frequency. Therefore, when the frequency is low,
the inductive reactanceis very low. This is whyan inductor allows the flow of DC and
low frequency AC: its reactance decreases withdecreasing frequency.

When the frequency ishigh, the inductive reactance is high. This is why an inductor
blocks the flow of highfrequency AC because its reactance increases with increasing
frequency.

Exercise 13 - 3

1. Describe what is meant by reactance.


2. Define the reactanceof a capacitor.


3. Explain how a capacitor blocks the flow of DC and low frequency ACbut allows
   the flow of high frequency AC.


4. Describe what is aninductor.


5. Describe what is inductance.


6. What is the unit of inductance?


7. Define the reactanceof an inductor.


8. Write the equation describing the inductanceof a solenoid.


9. Explain how an inductor blocks high frequency AC, but allows low frequency AC
   and DC to pass.