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1. There are two identical iron rods in front of you. One of them is a magnet, and the other
is not. Without using any other material, how can you find out which one is the magnet?
2. Magnetic compasses and magnetic dipping needles are instruments that you are given
to use. Describe their action if you are at the
a) north pole b) south pole c) equator
3. Explain why the magnetic field created by the electric currents flowing through the wires
in your home is unlikely to have any effect on a compass placed nearby.
4. The wire on the armature of an electric motor has a current of 15 A flowing through it.
The magnetic field produced by the permanent field magnet of the motor has a
magnitude of 0.20 T. If the wire is 25 cm long and remains perpendicular to the
magnetic field, what force does the wire experience?
5. A wire connecting a light to its power supply is 1.0 m long. The orientation of the wire
puts it perpendicular to the Earth's magnetic field. The Earth's magnetic field exerts a
force of 6.0 X 10-5 N on the wire when the current through the wire is 1.5 A. Calculate
the magnitude of the magnetic field of the Earth.
6. A power line has a DC current of 200 A flowing through it. The length of the wire
between suspension points is 50 m. The magnitude of the Earth's magnetic field in the
vicinity of the wire is 5.0 X 10-5 T, and the field is inclined at 45o to horizontal. If the wire
is running north and south, what is the magnitude of the force on the wire?
7. Alpha particles are projected downwards at a horizontal wire which is carrying current
towards the west. Which way will the alpha particles be deflected?
8. A magnetic field causes a charged particle to move in a circular path. If you consider
each of the following changes separately, how will the path of the particle change?
a) The magnetic field intensity is increases.
b) Added to the magnetic field, is an electric field which points in the same direction
as the magnetic field.
c) The electric field described in part (b), and the magnetic field are turned off at the
same time.
9. The magnetic force on a wire carrying 20 A of current is 0.40 N. The length of the wire
is 15 cm. If the wire is running perpendicular to the magnetic field responsible for the
force, what is the intensity of the magnetic field?
10. A wire of length 25 cm is angled at 45o to a magnetic field. The field intensity is 0.50 T.
If the wire carries a current of 4.0 A, what force is exerted on the wire?
11. A wire is placed on an electronic balance so that it is perpendicular to a magnetic field
of strength 0.20 T. The total mass of the wire is 0.015 kg, and the length is 40 cm. A
current is allowed to flow through the wire, and this current is increased until the
balance measures zero. What current will be flowing in the wire?
12. An electron is moving at 3.2 X 106 m/s [west]. It moves into a region where there is a
uniform magnetic field of strength 1.2 T [south]. What is the force on the electron?
13. In a certain region of space a magnetic field of magnitude 0.25 T exists. An alpha
particle enters the field at 90o to the field lines, after being accelerated from rest through
a potential difference of 1200 V . Calculate the magnetic force acting on the particle.
Remember that the charge and mass of the alpha particle is +3.2 X 10-19 C and
6.7 X 10-27 kg respectively.
14. An electron is moving in a vacuum with a velocity of 5.0 X 106 m/s [down], a distance of
0.10 m from a vertically oriented wire which is carrying current of 20 A upwards. What
is the force on the electron? Remember that force is a vector. Also, does the force
remain constant? Explain.
15. An air solenoid consists of 100 turns of wire and is 0.15 m long. A frame with a
conductor WXYZ is balanced horizontally inside the air solenoid as shown below.
The portions of the conductor labeled WX and YZ are each 5.0 cm long. The end
section of the conductor labeled XY is 1.5 cm long. If the current flowing through the
solenoid is 20 A, what current is needed in the conductor in order to balance the weight
(m = 1.8 X 10-2 g) which hangs from the end of the frame? Assume that the frame is
suspended at its center of mass.
16. The linear mass density of a wire is 150 g/m. This wire lies on top of another horizontal
wire in an apparatus. This top wire is supplied with a current of 40 A through very
flexible connecting wires which have an insignificant weight compared to the wire. The
wire is able to move up and down in nearly friction less guides. Determine the amount
of current that must flow through the bottom wire, in order to cause the top wire to float
4.0 cm above the bottom wire.
17. The radius of the path of an ionized particle of charge +e is 40 cm. The particle displays
circular motion because it is moving in vacuum, at 90o to a uniform magnetic field of
1.0 X 10-3 T. If the speed of the particle is 1.9 X 104 m/s, what is the particle's mass?
18. A uranium-235 atom has lost one electron, and has been accelerated through a
potential difference of 1.0 X 105 V. The mass of this atom is 3.9 X 10-25kg.
a) Determine what the velocity of the uranium-235 atom is.
b) If the atom travels at the speed you calculated in part (a), and perpendicular to a
magnetic field of 0.10 T, what would be the radius of its path?
January 17, 2014
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