Download presentation

Presentation is loading. Please wait.

1
**Happy New Year -2006 Champak Baran Das**

Physics Group (3242-S) Chamber Consultation: Friday 5.00 to 6.00 PM

2
**PHYSICS-II (PHY C132) Text Book: PHYSICS, VOL 2:**

by Halliday, Resnick & Krane (5th Edition) Reference Books: Introduction to Electrodynamics: by David J. Griffiths (3rd Ed.) Concepts of Modern Physics: by A. Beiser (6th Ed.)

3
**Electromagnetism deals with electromagnetic force and field**

Optics Electricity Magnetism

4
Electric Field An electric field is said to exist in the region of space around a charged object. When another charge object enters this electric field, an electric force acts on it.

5
**The test charge qo experiences an electric field E directed as shown.**

The electric field E at a point in space is defined as the electric force F acting on a unit positive test charge qo placed at that point : E = lim q0 q0 0 F

6
**Test charge should be small**

not to disturb the charge distribution of the source (a) For small enough qo, the distribution is undisturbed. (b) For a larger qo' , the distribution gets disturbed.

7
**Electric force and field**

+ q0 q1 r The Coulomb force is F= kq1q0/r2 (where, k = 1/40) The electric field at r = Force per unit charge , => E = F/q0 = kq1/r2

8
**Negative source charge**

q1 E Positive source charge E= kq1/r2 q1 E Negative source charge

9
**Negative source charge**

Electric Field Lines

10
**Begin on + charges and end on - charges.**

Electric Field Lines: a graphic concept as an aid to visualize the behavior of electric field. Begin on + charges and end on - charges. Number of lines entering or leaving a charge is proportional to the charge

11
**Electric Field Lines: (contd.)**

Density of lines indicates the strength of E at that point The tangent to the line passing through any point in space gives the direction of E at that point Two field lines can never cross.

12
Electric Field Lines Like charges (++) Opposite charges (+ -) .

13
Electric Dipole An electric charge dipole consists of a pair of equal and opposite point charges separated by a small distance, d. d +Q -Q

14
**Dipole Moment d Dipole moment p is a measure of the strength**

of the dipole and indicates its direction +Q -Q p is in the direction from the negative point charge to the positive point charge. d

15
**Electric Field of a dipole**

To find the electric field E at point P, At P, the fields E1 and E2 due to the two charges, are equal in magnitude. The total field is E = E1 + E2, E1 = E2 = kq/r2 = kq /(y2 +a2) The y components cancel, and x components add up => E || x-axis |E| = 2E1 cos . cos = a/r = a/(y2 +a2)1/2 E = k 2aq /(y2 +a2)3/2

16
**Electric Field of a dipole (cont’d)**

E = k 2aq /(y2 +a2)3/2 If y >> a, then E ~ k p/y3 E due to a dipole ~ 1/ r3 E due to a point charge ~ 1/ r2

17
**Electric Field of a dipole (cont’d)**

q -q x y To find the electric field at a distant point along the x-axis. The E field at any point x : When x >>> a, then x2 a2 ~ x2 E ~ 4kqa/x3

18
**Ex 26.11: Field due to Electric Quadrupole**

19
**Pr 26.4: Field due to Electric Quadrupole**

To find out E at P:

20
**A Dipole in Electric field**

The net force on the dipole is always zero. But there is a finite torque acting on it This torque tends to rotate it, so that p lines up with E.

21
**Dipole in a Uniform Electric Field**

Torque about the com = t = F x sin q + F(d-x)sin q = Fdsin q = qEdsin q = pEsin q = p x E x t = p x E

22
**Work done by external field E to rotate the dipole through an angle 0 to :**

23
**Choosing reference angle 0 = 90°**

Change in potential energy of the system: Choosing reference angle 0 = 90° and U(0 ) = 0.

24
**Ex 26.36: Dipole: q = 1.48 nC; d = 6.23 µm E (ext.) = 1100 N/C**

To find: (a) dipole moment p (b) difference in potential energy corresponding to dipole moment parallel and antiparallel to E. Ans. (a) p = 9.22 ×10-15 Cm (b) U = 2.03×10-11J

25
**Ex 26.37: Dipole: q = 2e; d = 0.78 nm E (ext.) = 3.4 ×106 N/C.**

To find: torque (a) p E (b) p E (c) p is opposite to E

Similar presentations

OK

There is a region near the origin of a coordinate system that you are told contains charges. You are not able to see them but have been asked to learn.

There is a region near the origin of a coordinate system that you are told contains charges. You are not able to see them but have been asked to learn.

© 2018 SlidePlayer.com Inc.

All rights reserved.

To make this website work, we log user data and share it with processors. To use this website, you must agree to our Privacy Policy, including cookie policy.

Ads by Google