Worksheet/Problems

Physics 11
Spring 2015
3/13 In Class 4–Review Problems before Exam 2
One thing missing is Chapter 18–Current, Ohm’s Law and Circuits!
1. A long, straight wire carrying a current of 20 A in the +y direction is
in a region of space where there is a uniform magnetic field of 4µT in
the +x direction.
(a) What is the magnitude and direction of the force on the wire?
(b) What is the net magnetic field (due to the uniform field and the
wire) at a point 30cm in the +x direction from the wire?
2. A long straight wire carries a current of 2A in the +x direction. An
electron is 25 cm below the wire and traveling at a speed of 3 × 105 m/s
in the +xdirection What is the force on the electron?
3. Two long, straight wires are 25cm apart on the surface of a table. The
one toward the top of the table carries a current of 2A to the right, the
lower one, 2A to the left. What is the force per unit length on each
wire? Magnitude and direction.
4. The entire table is covered with wires all carrying a current of 2A
toward the back of the table. The wires are uniformly spaced so that
there are 5 wires per centimeter from right to left on the table. Use
Ampere’s Law and a rectangle enclosing the wires to find the magnetic
field above and below the wires.
5. A wire loop in the shape of a rectangle rests on the surface of a table.
The loop is 30cm by 40cm–assume the 40cm direction is right-left. The
wire carries a current of 2A in the CW direction as you look down on
the table. There is a magnetic field of 4mT to the right everywhere on
the table.
(a) What is the force on each of the pieces of the loop?
(b) What is the net force on the loop?
(c) What is the torque on the loop?
6. For the following figures (there are five separate two-wire configurations), there is a current in the long straight wire or big loop; Its
direction is labeled. For the small loops, there is no current except the
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induced current. For each of the following, what is the direction of the
induced current in the small loop if the current I is increasing?
7. How would your answers to the last problem change if the current were
decreasing (instead of increasing)?
8. A circular loop of wire of radius 15cm is in the plane of the table. There
is a magnetic field of 5mT in the region. What is the flux through the
~ field is:
loop if the B
(a) Into the table?
(b) To the right?
(c) Toward the back of the table (still horizontal)?
(d) At an angle of 30◦ with respect to the table?
9. A circular loop of wire of radius 15cm is in the plane of the table. There
is a magnetic field of 5mT in the region. Over 4s, the field changes from
5mT up to 5mT down. What is the emf induced in the loop? What
direction will the induced current be?
10. A circular loop of wire of radius 15cm is in the plane of the table. There
is a magnetic field of 5mT down in the region. Over 4s, the radius of
the loop changes from 15cm to 5cm. What is the emf induced in the
loop? What direction will the induced current be?
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