Basic Physics II Assignments

We will have an exam covering chapters 16-19 on October 14

Start reading chapter 20 by October 2.

Homework for chapter 20, due Friday, October 16?

1. Find the magnitude of the magnetic force on a 3m length of wire that carries a 2A current if

a) the magnetic field is 0.03T and is perpendicular to the wire?

b) the same magnetic field makes an angle of 30^o with the wire?

2. The magnetic force on a wire 5m long is 0.12N when the current is 8A. The magnitude of the magnetic field is 0.005T. What is the angle between the field and the direction of the wire?

3. An electron is moving horizontally to the right of the page while a magnetic field is pointing horizontally into the page. What is the direction of the force on the electron?
4. An electron is moving with a velocity of 10^5m/s as shown. The Magnetic field is pointing in the – x direction and has a strength of 0.02T. a) Find the magnitude of the force on the electron. b) Find its direction.
5. A proton is moving toward a wire that carries current in the direction shown. a) What is the direction of the magnetic field produced at the proton by the current in the wire? b) What is the direction of the force on the proton?
6. The two long wires (a vertical one along the y axis and a horizontal one along the x axis) in the figure at the right carry a current of 12A in the directions shown. Find the magnetic fields they produce at two different places. The points and the wires are all in the same x-y plane. I suggest you calculate the field due to each wire at a particular point and then “add” them to get the total field at that point. Be sure to indicate the direction of the net field in each case. a) Find the total B at A, (x=3m, y=2m). b) Find the total B at C, (x=3m, y=-2m).
7. A long straight wire is 3m from the center of a circular loop of wire that is 1m in diameter. The plane of the wire is the same as the plane of the loop. The current in the long wire is 20A in the +x direction and the current in the loop is 10A (clockwise). What is the magnetic field at the center of the loop?

8. Two long straight wires run parallel to each other and carry currents of 20A and 15A respectively. The magnitude of the force on a 2m length of one wire is 0.05N. How far apart are they?

9. A long wire carries a current of 20A toward the left. It is 0.5m from the near edge of a rectangular “loop” of wire that carries a current of 10A counterclockwise around the loop. They all are in the x-y plane. The rectangle is 0.3m wide and 2m long. What is the net force on the rectangle due to the long wire?
10. You have two long straight wires carrying 15A currents in opposite directions. The Wires are 0.02m apart. a) Find the magnitude of the magnetic field at P1 half way between the wires. b) Find the magnitude of field the at P2, 0.2m above the top wire.

11. Repeat the above problem, but with the current in both wires pointing toward the right.

12. Three long wires are each carrying currents of 40A. The wires at C (x=4m, y=-3m) and at the origin (O) carry current into the page. The wire at A (x=4m, y=3m) carries current out of the page. a) Find the magnitude and direction of the force on a 0.7m length of the wire at the origin exerted by each of the wires at A and C. b) Find the magnitude and direction of the total force on a 0.7m length of the wire at the origin

Start reading chapter 21 by October 9.

Homework for chapter 21, due Friday, October 23?

1. The magnetic flux through a coil starts at 40 Wb and changes to 0 in 2s. What is the EMF induced in the coil during that time?

2. A circular coil 0.2m in radius has 100 turns of wire. The magnetic field is initially 0.2T into the plane of the coil. The field changes to 0.5T in 6s.

a) What is the change in flux through the coil?

b) What is the EMF induced between the ends of the coil?

3. The magnetic field at the right has a magnitude 0.1T into the page as shown at the right. The loop is initially in the plane of the page and has sides 0.3m and 0.6m a) Find the initial flux through the loop. b) Then the loop is rotated 37^o in a counterclockwise direction about the axis shown. Counterclockwise when looking down on the system from above. (It really doesn’t matter which way it is rotated for this question.) Now what is the flux through the loop? c) What is the change in the flux?

4. A circular loop is near a wire that is carrying current. There are two different cases, A and B. The currents are in the directions shown by the arrows. In both cases (A and B) tell which way the induced current will flow in each loop if the current is a) increasing in magnitude. b) decreasing in magnitude.
5. A copper bar is free to slide on two conducting rail 0.8m apart. A 10W resistor connects the two rails. The bar is moving to the left with a speed of 10m/s. There is a constant magnetic field into the page of magnitude 0.5T. a) What is the EMF generated in the loop? b) What is the current through the resistor? c) Which direction does the current travel through the resistor?
6. The flux through a loop changes as shown in the graph at the right. What average EMF is generated in the loop in each of the following time intervals? a) 0s < t < 0.2s b) 0.2s < t < 0.6s c) 0.6s < t < 0.8s
7. Consider the two loops at the right. They are facing each other. The front loop (A) has a current flowing in it in the counterclockwise direction when viewed from the front (the eye). Which way will the induced current flow in the second coil (B) if the current in A is a) Increasing? b) Decreasing?

8. A generator is used to generate a peak output voltage of 20V. The square armature consists of windings that are 10cm on a side and it rotates in a magnetic field of strength 0.4T at a rate of 50 cycles (or revolutions) per second. How many loops must be wound around the armature to produce the peak output voltage?

9. A transformer has a primary with 200 turns. How many turns must the secondary have to produce an output of 24V_rms if the voltage at the primary is 120V_rms?

10. A 2000W resistor, a capacitor and an inductor have the same reactance at a frequency of 2000Hz.

a) What is the capacitance of the capacitor?

b) What is the inductance of the inductor?