Physics 21 - Spring 2010
General organization of the course
Textbook by Halliday, Resnick, Walker Fundamentals of Physics, 8th edition, Extended Two hour-examinations (Feb. 16 and April 16) Two sets of homework per week Quiz each week Final examination At
Physics 21 Fall, 2008
Solution to HW-2
21-1 Excess electrons are placed on a small lead sphere with a mass of m = 8.40 g so that its net charge is Q = 4.00 109 C. (a) Find the number of excess electrons on the sphere. (b)How many excess electrons
Lecture-3
Chapter 22 Electric Fields
Field: a spatial distribution of a physical quantity, e.g., the temperature field in Pennsylvania the magnetic field around the earth the electric field of a cell phone provider.
3/26/10
In principle, we can define the
Physics 21 Fall, 2008
Solution to HW-15
28-39 A long, straight, cylindrical wire of radius R carries a current uniformly distributed over its cross section. At what location is the magnetic eld produced by this current equal to half of its largest
Physics 21
Fall, 2010
Solution to Hour Exam #1
The graders for the problems were:
1 Jones, 2 Faust, 3 Malenda, 4 and 5 Beels
For questions about the grading, see the grader by Oct. 27.
(b) (3 pts.) Determine the currents I1 , I2 , and I3
(including the co
Physics 21
Fall, 2011
Solution to HW-7
24-25 A 6.60 F, parallel-plate, air capacitor has a plate
separation of 3.00 mm and is charged to a potential dierence
of 300 V. Calculate the energy density in the region between
the plates.
1
Energy density is calc
PHY21, Prof. I. Biaggio
Narrative due: Fri 09/16/2016 Final solution due: Fri 09/23/2016
Learning Homework 3 Narrative
3.1
Energy of the electric field
The two parallel sheets of charge are a nice symmetric confguration. One can use Gauss Law
to find the
Physics 21
Fall, 2011
Solution to HW-6
23-9 A point charge q1 = 4.10 nC is placed at the origin,
and a second point charge q2 = 2.9 nC is placed on the
x-axis at x = +21.0 cm. A third point charge q3 = 2.1 nC
is to be placed on the x-axis between q1 and q
Physics 21
Fall, 2011
Solution to HW-5
For surface S5 , the normal direction is in the +x direction,
so we integrate the component over the surface.
i
L
L
22-4 A cube has sides of length L = 0.330m. It is placed
with one corner at the origin as shown in t
Physics 21
Fall, 2011
Solution to HW-4
22-7 The electric eld due to an innite line of charge is
perpendicular to the line and has magnitude E = /2 0 r.
Consider an imaginary cylinder with a radius of r = 0.200 m
and length l = 0.465 m that has an innite l
Physics 21
Fall, 2009
Solution to Hour Exam #2
If you want to discuss the grading, you must speak with the grader by Nov. 20.
1: Beels 2: Malenda 3: Belony 4 and 5: Drake
Problem 1. For the following circuit
this circuit that is approximately to scale. In
Physics 21
Fall, 2011
Solution to Hour Exam #1
The graders for the problems were:
1 Tupa, 2 Faust, 3 Beels, 4 Malenda, 5 Glueckstein
For questions about the grading, see the grader by Oct. 26.
(b) (3 pts.) Determine the currents I1 , I2 , and I3 (includin
Physics 21
Fall, 2010
Solution to Hour Exam #2
If you want to discuss the grading, you must speak with the grader by Dec. 8.
1: Beels 2: Jones 3: Faust 4: Beels 5: Glueckstein
Problem 1. For the following circuit:
(b) (3 pts.) Evaluate the peak value of t
Physics 21
Fall, 2011
Solution to HW-3
21-96 Positive charge Q is uniformly distributed around
a semicircle of radius a. Find the electric eld (magnitude
and direction) at the center of curvature P .
y
dQ = ds
= ad
From this result we see the E has a mag
Physics 21
Fall, 2011
Solution to HW-24
16-33 Two loudspeakers, A and B , are driven by the same
amplier and emit sinusoidal waves in phase. Speaker B is
2.00 m to the right of speaker A. Consider point Q along
the extension of the line connecting the spe
Physics 21
Fall, 2011
Solution to HW-8
25-44 If a 75 W bulb (75 W are dissipated when connected across 120V) is connected across a 220 V potential
dierence (as is used in Europe), how much power does it
dissipate?
(a) The power dissipation P and potential
Physics 21
Fall, 2011
Solution to HW-23
K 20-53 One way to monitor global warming is to measure
the average temperature of the ocean. Researchers are doing
this by measuring the time it takes sound pulses to travel underwater over large distances. At a de
Physics 21
Fall, 2011
Solution to HW-22
K20-7 The wave speed on a string under tension is
170 m/s. What is the speed if the tension is doubled?
From Eq. (3) in the waves handout,
v=
T /,
so if the tension T is doubled, v increases by
2.
K20-11 A wave trav
Physics 21
Fall, 2011
Solution to HW-20
31-21 You have a 207 resistor, a 0.408 H inductor, a
4.99 F capacitor, and a variable-frequency ac source with
an amplitude of 2.93 V. You connect all four elements together to form a series circuit. (a) At what fre
Physics 21
Fall, 2011
Solution to HW-19
29-34 A dielectric of permittivity 3.3 1011 F/m completely lls the volume between two capacitor plates. For t >
0 the electric ux through the dielectric is (7800 V m/s3 )t3 .
The dielectric is ideal and nonmagnetic;
Physics 21
Fall, 2011
Solution to HW-18
30-7 At the instant when the current in an inductor is increasing at a rate of 6.45 102 A/s, the magnitude of the
self-induced emf is 1.65 102 V. (a) What is the inductance of the inductor? (b) If the inductor is a
Physics 21
Fall, 2011
Solution to HW-17
29-7 The current in the long, straight wire AB shown in
the gure is upward and is increasing steadily at a rate di/dt.
(a,b) At an instant when the current is i, what are the magnitude and direction of the eld B at
Physics 21
Fall, 2011
Solution to HW-16
F=
28-48 The current in the windings of a toroidal solenoid
is 2.400 A. There are N = 500 turns and the mean radius is
r = 25.00 cm. The toroidal solenoid is lled with a magnetic
material. The magnetic eld inside th
Physics 21
Fall, 2011
Solution to HW-15
28-32 A solid conductor with radius a is supported by insulating disks on the axis of a conducting tube with inner
radius b and outer radius c. The central conductor and tube
carry equal currents I in opposite direc
Physics 21
Fall, 2011
Solution to HW-14
Cancelling Magnetic Field Four very long, currentcarrying wires in the same plane intersect to form a square
with side lengths of 39.0 cm, as shown in the gure. The currents running through the wires are 8.0 A, 20.0
Physics 21
Fall, 2011
Solution to HW-13
28-12 Two parallel wires are 5.00 cm apart and carry currents in opposite directions, as shown in the gure. Find
the magnitude and direction of the magnetic eld at point
P due to two 1.50-mm segments of wire that ar
Physics 21
Fall, 2011
Solution to HW-12
27-36 A straight, vertical wire carries a current of I =
1.19 A downward in a region between the poles of a large
superconducting electromagnet, where the magnetic eld B
has a magnitude of B = 0.591 T and is horizon
Physics 21
Fall, 2011
Solution to HW-10
27-3 In a 1.35 T magnetic eld directed vertically upward,
a particle having a charge of magnitude 8.90 C and initially
moving northward at 4.72 km/s is deected toward the east.
(a) What is the sign of the charge of
Physics 21
Fall, 2011
Solution to HW-9
Set up the loop equation for this new loop:
25 V (50 )I = 0 = I =
26-27 In the circuit shown in the gure the batteries have
negligible internal resistance and the meters are both idealized. With the switch S open, th
Prof. I. Biaggio PHY 21 due: W'ed 04/04/2012
Homework 10
10.1 A Circuit with a Couple of loops (4 pts)
Here is a circuit with two batteries working inside the same cir-
cuit. The loops on the left dont have any resistance and are
electrically isolated
Prof. I. Biaggio PHY 21 due: Wed 03/28/2012
Homework 9
9.1 Capacitors (3 pts)
Two conductors insulated from each other are used to build a capacitor. The capacitance C of a capacitor
gives the absolute value of the total charge Q that can be stored on o
Prof. l. Biaggio PHY 21 due: Wed 02/29/2012
7.3 [TB 29.52 7 adapted] Coil in a jittery magnetic eld (3 pts)
A at coil is oriented so that its wires are perpendicuiar to a spatially uniform magnetic eld. The magnitude
of this eld varies with time according
Prof. I. Biaggio PHY 21 due: Wed 02/22/2012
Homework 6
6.1 Loop 'l?
A circular conducting coil with N turns of wire is rotating with angular velocity to around its diameter The
coil has a radius r, and 1s inside an homogenous magnetic eld B that is perpen
Prof. I. Biaggio ' PHY 21 due: Wed 04/18/2012
Homework 12
12.1 Basic polarizer questions (4 pts)
A light beam is initially unpolarized, and it is passed through a polarizer with a vertical axis. The intensity of
the beam emerging from the lter is 10 W/m