Question

1. If you have a magnet and a stationary closed loop of wire, is there any way to produce a current in the wire? If so, how can you do it? If not, why not?

2. Imagine you have two wire loops. The first one is connected to an AC power supply and produces a (time varying) magnetic field. The second one reacts to this time varying field according to Faraday's law. Describe the current produced in the second loop.

3. Imagine you have two wire loops. The first one is now connected to a power supply and produces a magnetic field. The second one reacts according to Faraday's law. Does the second produce a current? Why is this situation different than with the AC power supply?

Answer #1

Imagine that you have a closed loop of wire sitting on a table
and a bar magnet in your hand. You are allowed to move the magnet
any way you’d like, but you may not touch the wire. Is there a way
for you to produce a current in the wire? If so, how can you do it?
If not, why not?
Imagine you have two wire loops lying next to each other on a
table. The first one is...

Imagine you have two wire loops lying next to each other on a
table. The first one is connected to a DC power supply (like a
battery), producing a constant current through the wire, which in
turn produces a magnetic field. The second wire loop reacts to this
magnetic field according to Faraday's law. Does the second wire
loop have any current flowing through it? Why/how is this situation
different than with the AC power supply in the previous
question?

Written Problem: Induction from a falling
magnet
We have a small magnet with a magnetic moment of m = 0.1
Am2 (remember: magnetic moment is defined as m = IA -
see page 932 of book for the definition). We also have coils of
wire. The coils are made out of 100 circular loops of a single
wire. A single loop has a radius of 10 cm. The thickness of the
wire has a circular cross section with a 0.5...

1. To get the wire loop to spin we will strip [x amount] of the
copper off at least one or both wires.
all
none
half
≈
2. To get the wire loop to spin we will strip [see question 1]
of the copper off both ends of the wire to increase the [y]
experienced by the motor.
magnetic field
cross sectional area
torque
current
3. How fast the motor spins is related to the amount of force
acting on...

1. A long solenoid with 500 turns of wire, length L=80cm and
diameter d=2.5cm. The center of the solenoid is surrounded by a
circular loop of wire with a diameter dloop=5.0cm and a
resistance R=0.50ohm. The axis of the solenoid is also the axis for
the loop.
a. What is the magnetic field inside the solenoid when a current
of 2.0A passes through the solenoid? [note: the magnetic field
inside the solenoid is uniform and there is no magnetic field...

A magnetic field passes through a stationary wire loop, and its
magnitude changes in time according to the graph in the drawing.
The direction of the field remains constant, however. There are
three equal time intervals indicated in the graph: 0—3.0 s, 3.0—6.0
s, and 6.0—9.0 s. The loop consists of 40 turns of wire and has an
area of 0.21 m2. The magnetic field is oriented parallel to the
normal to the loop. For purposes of this problem, this...

You have a 20cm x 30cm rectangular loop of wire carrying 15 Amps
rms ac. What is the rms magnetic field in the center of the
loop?

1) You decide to build a small generator by rotating a coiled
wire inside a static magnetic field of 0.40 T. You construct the
apparatus by coiling wire into 5 loops of radius 0.19 m. If the
coils rotate at 2.0 revolutions per second and are connected to a
device with 120Ω resistance, calculate the average power Paverage
supplied to that device.
2) A 121‑turn circular coil of radius 2.99 cm and negligible
resistance is immersed in a uniform magnetic...

17.1) Helmholtz coils
The magnetic field on the axis of a circular loop of wire is
not very uniform (in fact, we showed that the field
strength decreases as 1/r3
). But, with two such coils, one can produce a relatively
uniform field in a small
neighborhood.
Consider two parallel circular coils of radius a, centered on
the y-axis. One coil is in the y = 0 plane, and the
other is in the y = d plane. Assume that...

3.Explain why if a CD power supply is used, only when the power
supply is turned on or of there is an induced current in the second
coil (secondary).
4. Explain why when the switch is on, and there is a direct
current through the circuit, there is no induced electric current
in that coil.
Electromagnetic Induction
I. Objectives
1. Verify the Faraday-Lenz‘s Law
2. Perform measurements with a set of coils to understand how a
transformer works.
II. Theory
In...

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