Coulom

b’s Law

• Charles Coulomb (1736-1806: French)–Studied relationship between

force and charge Unit of charge = 1 coulomb (C)

The charge on 1 electron is (1.6 x 10-19 C)

Coulom

b’s Law

• The LAW!– Force directly related to magnitude of

the charges– Force inversely related to the square of

the distance between the two charges

F = r2

kqQF α q Q

r2

1F α

r2

q QF αk is a constant that corrects the proportion into an equality.

F = r2

k qQ

• This is similar to a formula • we talked about in Lesson 5.

Only Attractiv

e

Attractive or

Repulsive

F = r2

G mM

Newton’sLawOf

Universal Gravitation

Coulomb’sLaw

Coulom

b’s Law

Product of

masses

Product of

charges

F = r2

G mM

F = r2

k qQ

• Keep comparing:

Coulom

b’s Law

• Keep Comparing:

Both areinverse-squarelaws

F = r2

G mM

F = r2

k qQ

• Keep Comparing

F = r2

G mM

9 x 109 N·m2/C2

Large Magnitude

6.67 x 10-11 N·m2/kg2

Small Magnitude

F = r2

k qQ

Exponent Keys on Calculators: Borrow one from your instructor. Ipods and cell telephones don’t work well with exponent keys.

TI 30: 2nd EETI 83: 2nd EE

Others: Might see exp, or x 10x These keys are used when decimal places are too many for the calculator to display or use.

A number like .0000000000000000000000000003 so it needs to be typed by using the exponent key. TI 30: 3EE-28, others: 3exp-28

More Practice:

56900000000000000000000000

5.69EE25

.000000000000000000000256

2.56EE-22

Coulom

b’s Law

F= r2kq Q

• Sample problem 1! YEAH!–What is the magnitude of the

electrostatic force between 2 protons in the nucleus? (assume the distance to be 3.0x10-13 cm)

(9 E109)=

(1.6 E10-

19)(3.0 E 10-15

)2

F=25.6 N

(1.6 E 10-

19)

Coulom

b’s Law

F= r2

G mM

• Sample problem 2! – What is the magnitude of the gravitational

force between 2 protons in the nucleus? (assume the distance to be 3.0x10-13 cm)

(6.67 x 10-11)

=(1.67 x 10-

27 )(3.0 x 10-15 )2

F= 2.07x10-35 N

(1.67 x 10-27)

Electric Fields: An area around a charged object that affects all other charged objectsUnit: N/C

The more the lines the stronger the field

Two More Rules for Drawing Electric Field Lines:

Lines are always drawn out of the positive and into the negative.

The more the lines the stronger the field.