2. C
The induced emf,
e,
from a bar of length l moving along rails at a speed
v in a magnetic field of magnitude
B is given by the formula
e
= vBl. Since we are given the
values for v,
B, and l, this is simply a
matter of plugging numbers into a formula. Remember that we need to convert to
units of meters:
div>
3. A
Magnetic flux is given by the formula
F = B.A = BAcos?
,
where B is the magnetic field
strength, A is the area, and
?
is the angle between the magnetic field vector and a vector pointing
perpendicular to the area. In this case, the value of
?
is 90°, and since cos
90° = 0,
the magnetic flux through the area is zero.
A more intuitive way of thinking about this problem is to see that, since the
magnetic field lines pass across the triangle rather than through it, there are
no magnetic field lines passing through the area, and so the flux is equal to
zero.
4. E
A generator, also called a dynamo, is normally run by a gas-powered motor that
rotates a coil in a magnetic field, thereby inducing emf and generating an
electric current.
5. C
The relationship between the voltage in a primary coil and in a secondary coil
is given by the formula:
Since the primary has an emf of 5.0 V, and
the secondary has twice as many turns as the primary, the secondary has an emf
of 10 V.
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