### Solution

```B = BA Cos 
Example 1.1
A coil consists of 200 turns of wire. Each turn is a square
of side 18 cm, and a uniform magnetic field directed
perpendicular to the plane of the coil is turned on. If the
field changes linearly from 0 to 0.50 T in 0.80 s, what is
the magnitude of the induced emf in the coil while the
field is changing?
Solution
Since  = zero  cos 0 = 1
4.05 volts
Example 1.2
Consider a single circular loop (or coil) with a 2.50-cm radius in a constant
magnetic field of 0.625 T. Find the magnetic flux through this loop when it’s
normal makes an angle of (a) 0o, (b) 30.0o, (c) 60.0o, and (d) 90.0o
with the direction of the magnetic field B.
Solution
  BA cos  Br 2 cos
(a)   0.625T  0.025 cos0o  1.23103 Wb
2
(b)   0.625T  0.025 cos30o  1.07 103 Wb
2
(c)   0.625T  0.025 cos60o  6.1510 4 Wb
2
(d)   0.625T  0.025 cos90o  0
2
Example 1.3
The induced emf in a single loop of wire has a magnitude of
1.48 V when the magnetic flux is changed from 0.850 T.m2 to
0.110T.m2. How much time is required for this change in flux?
Solution
Using equation 1.3
The induced current
in a loop is in the
direction that creates
a magnetic field that
opposes the change in
magnetic flux through
the area enclosed by
the loop.
Motors are devices into which energy
is transferred by electrical transmission
while energy is transferred out by work.
Essentially, a motor is a generator
operating in reverse. Instead of
generating a current by rotating a coil,
a current is supplied to the coil by a battery
```