Physics 32

Elementary Physics II

Course description

• This course is the second part of a series of calculus-based elementary Physics courses taken by students majoring in science. It aims to develop the student’s analytical and problem solving skills through take-home problem sets, class recitations, long exams, and lectures. It covers the fundamental concepts of electricity and magnetism. Topics include electrostatics, DC circuits, magnetic fields and its sources, magnetic induction, AC circuits, Maxwell’s equations and electromagnetic waves.

Course objectivesThe course is a combination of lecture and laboratory experiments. In the

lecture, the students will1. acquire a fundamental understanding of the ideas and concepts

presented as they pertain to electric fields, magnetic fields, induction, DC and AC circuits, electromagnetic waves;

2. experience how physics is used to describe, predict and explain many natural phenomena;

3. develop critical thinking skills and be exposed to scientific process and method, i.e., develop a systematic, logical approach to problem-solving that can be applied to problems in physics and to problems in general and to acquire a certain level of intuition for physical phenomena;

4. develop the ability to recognize the appropriate physics that applies in any given physical situation;

5. be provided with skills needed to continue learning throughout their lives;

6. develop an awareness and appreciation of some of the achievements and limitations of physics.

Course outline and schedules

• Electric charge and electric field (15-16/04)• Gauss’ law (17-20/04)• Electric potential (21-22/04)• Capacitance and dielectrics (23-24/04)• Current, resistance and electromotive force (27-28/04)• Direct current circuits (29-30/04)• Magnetic field and magnetic forces (05-06/05)• Sources of magnetic fields (07-08/05)• Electromagnetic induction (11-12/05)• Inductance (13-14/05)• Alternating waves (15-18/05)• Electromagnetic waves (19-21/05)

Required readings (Textbook)• H. Young and R. Freedman, University Physics 12th edition,

Pearson/Addison-Wesley, 2008.

Suggested readings (References)

• Resnick, R., Walker, J. Fundamentals of Physics, Wiley, 2004.• Serway, R., Jewett, J., Physics for Scientists and Engineers 7th ed., Brooks Cole, 2007• Tipler, P., Mosca G., Physics for scientists and engineers 6th ed., W.H. Freeman, 2007• Giancoli, D., Physics: Principles with applications, Pearson Education, 2004• Giancoli, D., Physics for scientists and engineers with modern physics 4th ed., Prentice Hall, 2008• Knight, D., Physics for Scientists and Engineers: A Strategic Approach with Modern Physics and

MasteringPhysics (2nd Edition) (MasteringPhysics Series), Addison-Wesley, 2007.

Course requirements

• Evaluation in this course will be based on assignments, two long exams and one final exam.

• Grade computation:• Final Lecture grade = 80% (2 Long exams +

Total assignments) + 20% (Final exam)• FIRST LONG EXAM (04/05)• SECOND LONG EXAM (22/05); • FINAL EXAM (25-27/05)

Grading system/ Consultation hours

• 92-100 A• 84-<92 B+• 76-<84 B• 68-<76 C+• 60-<68 C• 50-<60 D• Below 50 F

• Wednesday 1030-1200 (by appointment)

• Email: nlagrosas@ateneo.edu.

Classroom policies

• In order to pass this course, laboratory grades must be at least 50% or better.

• No make-up exams will be given on all missed (for any reason) exam.

• Academic dishonesty is a serious offense. If you are caught cheating or plagiarizing reports, your score will be negative of the perfect score.

• Final exam is a comprehensive exam.

Electric Charge

Coulomb's Law:Like charges repel, unlike charges attract.

where ε0 = permittivity of space

Coulomb's Constant

Static charge

electric charge accumulated on an object.

http://weathereye.kgan.com/cadet/lightning/safety.html

Where is the best place to hide during lightning?

Electric charge is conserved!

The algebraic sum of the all the electric charge in any closed system is constant.

The magnitude of charge of the electron or proton is a natural unit of charge.

Charge is quantized.

Conductors permit the easy movement of charges through the material. Insulators do not permit the easy movement of charges through the material

Ways of charging:

1. Charging by friction and contact

2. Charging by induction

Coulomb's Law:The magnitude of the electric force between two point charges is directly proportional to the product of the charges and inversely proportional to the square to the square of the distance between them.

Superposition of forcesThe total force acting on a charge due to other charges (in the vicinity of the charge in question) is the vector sum of the force exerted by each individual charge.

Example. Two similar conducting balls of mass m are hung from silk threads of length l and carry similar charges q. Assume that is small. Show that the distance between the two charges is

3/12

2

mg

lqx

o

l l

Example. Two identical conducting spheres, having charges of opposite sign, attract each other with a force of 0.108N when separated by 0.5m. The spheres are connected by a conducting wire, which is then removed, and thereafter repel each other with a force of 0.0360N. What were the initial charges on the spheres?

Electric field and electric forces

The electric force on a charged body is exerted by the electric field created by other charged bodies.

An electric field line is defined as a line drawn tangent to the electric field vector at each point in space.

Electric field lines from different charge configurations

Electric Field

Electric field is defined as the electric force per unit charge.

http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

Point charge

Parallel plate

Infinitely long wireCross section

For a positive point charge:

For a negative point charge:

Superposition of electric fields:

The direction of the electric field at any point is tangent to the field line through this point.

Example. Calculate the electric field of a ring of charge at a point a distance x from the axis of the ring. Assume that the ring has a constant linear charge density. Where is the location of maximum E?

R

x

Electric dipoles

An electric dipole is a pair of point charges with equal magnitude and opposite sign.

Water molecule: an electric dipole

An electric dipole exposed to an external electric field:

Equipotential lines

For water molecule, p=6.13x10-30Cm.

Example. What is the form of the electric field at a point r from an infinitely long wire?Example. Given an object with a flat and a high curvature surface, which region will have a the strongest electric field? Why?

Gauss’ Law

The total electric flux through a closed surface is equal to the total (net) electric charge inside the surface, divided by . o