# Physics

posted by Jake

1.
A rectangular coil 0.065 m by 0.080 m is positioned
so that its cross-sectional area is perpendicular
to the direction of a magnetic field.
The coil has 66 turns and a total resistance of
7.6 Ω and the field decreases at a rate of 2.5
T/s.
What is the magnitude of the induced current
in the coil?

2.
A student attempts to make a simple generator by passing a single loop of wire between the poles of a horseshoe magnet with a magnetic field of 2.0 ×10−2 T. The area of the loop is 4.87 ×10−3 m2 and is moved perpendicular to the magnetic field lines.
In what time interval will the student have
to move the loop out of the magnetic field in
order to induce an EMF of 1.9 V?

3.
A student attempts to make a simple generator
by wrapping a long piece of wire across
a cylinder with a cross-sectional area of 1.076×10−3 m2. She then passes the coil betweenthe poles of a horseshoe magnet with a magnetic field of 2.2 ×10−2 T. The student finds that by removing the coil perpendicular to the magnetic field lines during 0.29 s, a voltage drop of 145 mV can be induced across the wire.
How many turns of wire are wrapped
around the coil?

4.
A bolt of lightning, such as the one shown on
the left in the figure, behaves like a vertical
wire conducting electric current. As a result,
it produces a magnetic field whose strength
varies with the distance from the lightning. A
139-turn circular coil with a radius of 0.842
m is oriented perpendicular to the magnetic
field as shown. The magnetic field at the coil
drops from 4.99×10−3 T to 0.00 T in 10.7 µs.
What is the average emf induced in the
coil?

1. bobpursley

a. EMF=N*area*dB/dt
then current= EMF/resistance

b. EMF= above, solve or dt.

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