Chapter 12 Electromagnetic Induction
221
Therefore, we can analyze this circuit as if the
inductor is not there.
Once the switch is closed, the magnetic
fi eld expands and remains constant. At that
point, the current levels off and you can use
Ohm’s law to solve for I, E, and R. The inductor
will have no effect on the circuit.
Note in the equivalent circuit shown in
Figure 12-14 that only voltage (E) and resis-
tance (R) are given. Based on these values, you
can solve this circuit for current (I) by using
Ohm’s law:
I =
E
__
R
I =
10 V
_____
20 Ω
I = 0.5 A or 500 mA
More information is required before you
can analyze these circuits with inductor and
resistor combinations in ac circuits. Chapter 14
explains how to solve these more diffi cult
circuits.
Figure 12-14. Since an inductor has no effect on
the constant current fl ow of a dc power supply, it
can be left out when solving circuit problems.
Equivalent
circuit for DC
R1 = 20
R1 = 20 S1
L1 = 12 mH E = 10 V
E = 10 V
the circuit shown in Figure 12-14. You recall
that an inductor has no effect on a dc circuit,
except when the switch is closing or opening.
This means that you must fi nd the square root of 16. In the
electronics formulas that you will see, you will have to fi rst do
other computations before fi nding the square root of the number.
For example, you may have to multiply some numbers fi rst before
fi nding the square root:
√2
_____
× 8
√4
_____
× 4
√16
___
4
Practice Problems
Find the square root of the following perfect squares.
1. √100
____
2. √25
___
3. √144
____
4. √64
___
5. √81
___
6. √3
_____
× 3
7. √2
________
× 3 × 6
8. √2
_________
× 6 × 12