physics 2 lecture 5 - electrostatics and electrodynamics

8/11/2019 Physics 2 Lecture 5 - Electrostatics and Electrodynamics

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LESSON 5

Prepared by :

Pro f. Michael M. Salvahan

Electrostatics and Electrodynamics



Quo te for the Day

No mat ter how many

m is takes you make or howslow you progress, you

are st i l l way ahead ofeveryone who isn’t try ing .



Electr ic Charge

Two Kinds of Electric Charge

1. Positive

2. Negative

Electric charge is conserved.

“If a certain amount of one type ofcharge is produced in a process, an equal

amount of opposite type is produced.”



Electr ic Charge

Electric Charge

1. Proton Charge = 1.602 x 10-19 C

2. Electron Charge = - 1.602 x 10-19

C

1 C = 6.25 x 1018 e

1 e = 1.602 x 10-19 C



Coulomb’s Law

Coulomb’s Law

Suppose that two point charges, Q1 and

Q2 are at a distance r apart in vacuum, If Q1and Q2 have the same sign, the two charges

repel each other, if they have opposite signs,

they attract each other.

= 2

2 k = 1

4 πε

(in vacuum) k = 9 x109 •2

2



Coulomb’s Law

Coulomb’s Law

When the surrounding medium is not a

vacuum, forces caused by induced charges inthe material reduce the force between point

charges. If a material has a dielectric

constant K, then εo will be replaced by Kεo =

ε.

= 2

• 2 k =

1

4 πε

K = ε / εo



Coulomb’s Law

Sample Problems

1. A glass rod rubbed with silk acquires a

charge of +80.0 x 10

-10

C.

a. What is the charge on the silk?

b. How many electrons have been

transferred to the silk?

a. – 80.0 x 10-10 C

b. No. of electrons = 5.00 x 10

10

electrons



Coulomb’s Law

Sample Problems

2. Two particles having a charge of -1.0 μC

and -2.0 μC are separated by a distance of0.30m. What is the electrostatic force on each

particle?

F = 0.20 N



Coulomb’s Law

Sample Problems

3. Two charges are separated to distance of

100 cm, causing the electric force betweenthem to increase by a factor of exactly 5.

What was their initial separation distance?

r 1 = 2.24 m



Coulomb’s Law

Sample Problems

4. Two coins lie 1.5 m apart on a table. They

carry identical charges. Approximately howlarge is the charge on each if a coin

experiences a force of 2 N?

Q = 2 x 10-5 C



Coulomb’s Law

Sample Problems

5. An isolated electron experiences an electric

force of 3.2 x 10

-14

N. What is the electric fieldat the electric location?

E = 2.0 x 105 N/C



Coulomb’s Law

Sample Problems

6. A proton is accelerated eastward at 1.84 x

10

9

m / s

2

by an electric field. Determine themagnitude and direction of the electric field.

mp = 1.673 x 10-27 kg

E = 19.25 N/C, eastward

physics 2 lecture 5 - electrostatics and electrodynamics

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