Exam 3

Welcome to the Physics 24 Exam!

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Don’t forget to pick up your test preparation homework.

Mad

ison

Parris

Pringle

Up

shaw

l

Wad

dill

Kurter

With my chainsaw in my left hand, my right hand is free for the right hand rule!

Do you know your exam room?

Announcements

Pick up test preparation homework from the back of the lecture hall or download from here.

Updated course grades will hopefully be available by 3:00 pm on the day after the exam. Grades spreadsheets will not be updated over the weekends after exams.

Know the exam time!

Find your room ahead of time!

If at 5:00 on test day you are lost, go to 104 Physics and check the exam room schedule, then go to the appropriate room and take

the exam there.

Exam is from 5:00-6:00 pm!

Physics 2135 Test Rooms, Spring 2015:

Instructor Sections RoomDr. Kurter F, H 104 PhysicsDr. Madison E, G 199 ToomeyDr. Parris K, M 125 Butler-Carlton (Civil Eng.)Mr. Upshaw A, C, J, L G-3 SchrenkDr. Waddill B, D G-31 EECH (Electrical Eng.)

Special Accommodations Testing Center

Exam 3

Review

The problems in this lecture are the standard “exam review lecture” problems and are not a guarantee of the exam

content.

Please Look at Prior Tests!

Contents:

important note

Biot-Savart law

magnetic field of wires

Lenz’s Law

motional emf, with gravity

electromagnetic waves

Two long parallel conductors carry currents in the same direction as shown. Conductor A carries a current of 150 A, and is held firmly in place. Conductor B is free to move up and down. If the mass per unit length of conductor B is 0.10 kg/m what is the value of the current IB in conductor B so that the net force on conductor B is zero when it is 2.50 cm below

conductor A?

IA = 150 A

IB

2.50 cm

The magnetic force on wire B due to the current in wire A is

B B B AF =I L B .

This equation was introduced before exam 2, but is “fair game” for exam 3!

Similarly, this equation is “fair game” for exam 3:

q q q'F =qv B

A conductor consists of a circular loop of radius R and two long straight sections as shown. The straight sections are radial. The wire lies in the plane of the paper and carries current I. Determine the magnitude and direction of the magnetic field at the center of the loop (assume the gap in the loop is negligible).

I P

I1 = 6.0 A I2

Q 0.50 m 0.50 m

1.00 m P

Two long parallel conductors are separated by 1.0 m. The wire on the left carries a current I1 = 6.0 A into the page. (a) What is the direction and magnitude of I2 in order for the net magnetic field at point P to be zero? (b) What is the magnitude and direction of the net magnetic field at point Q?

A long straight wire carries a current I. Near the wire is a square conducting loop that includes a battery and a switch, as shown in the diagram. (Assume the battery and switch are small enough that all sides of the square loop have the same effective length.)

When the switch is closed, in what direction will the square loop accelerate?

I

+-

A horizontal wire is free to slide on the vertical rails of a conducting frame as shown. The wire has mass per unit length and length D, and the resistance of the circuit is R. If a uniform field is directed perpendicular to the frame and out of the page, what is the terminal speed of the wire as it falls under the influence of gravity?

Dl

Bout

R

At what distance from a 100 W electromagnetic wave point source does Emax = 15.0 V/m? What is the average energy density of the electromagnetic wave at that point?

A 100 mW laser beam is perfectly reflected directly back on itself by a mirror. Calculate the force the laser beam exerts on the mirror.

20 max

1 PI S c E

2 A

r ad

I 2IP or

c c

22 max

0 max0

B1 1u = E =

2 2

5.16 m 9.96x10-10 J/m3

6.67x10-10 N