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20-2 Coulomb’s Law

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20-2Coulomb’s Law

q1q2

Fe = kc

r2

1780’s

Charles Coulomb was experimenting to find how charges create forces

The force depends on

- Charges
- Distance
He found this relationship

kc = Coulomb’s Constant

kc = 8.99x109 Nm2/C2

The elementary charge of both protons and electrons are the same. One is + and one is -

q = 1.60x10-19 C

This is the smallest possible charge. When a particle is charged, it is always a multiple of this number.

(It is QUANTIZED)

n +

+ n

e-

Find the force between the nucleus and an electron and an helium atom if they are separated by 1.00 nm (remember that n=nano=10-9).

q1 = 2(1.60x10-19) C

q2 = 1.60x10-19 C

1

2

3

2 m

1 m

q1 = - 6 mC

q2 = +2 mC

q3 = - 3 mC

1

3

What would change if this were the original orientation?

2

Find the net force on q3

1

2

3

2 m

x

q1 = - 6 mC

q2 = +2 mC

q3 = - 3 mC

What is the value of x if q2 is in equilibrium?

Conductors and Insulators

Conductors – any material that allows charges to flow through it easily.

examples:

Insulators – a material that does not allow charges to move.

examples:

Both can be charged. It is the movement of charges that makes them different.

Electroscope

Charging by Conduction

Objects touch and transfer charges. The object will acquire the same charge as the original charge.

Charging by Induction

Objects do not touch. The object is grounded while a charge is brought close. The object will acquire the opposite charge.