Transcript Chapter 21

Chapter 21
Electric Charge
Like charges repel and unlike charges attract
We take the convention that the charge on the glass rod is
“positive” and the charge on the rubber rod is negative.
Negatively charged electrons transfer from glass to silk, and from
fur to rubber.
Charge is quantized: q = N e
Conductors: charges move quite freely (e.g. copper, silver
aluminum,..etc.). Redistribution of charge..
Insulators: charges are ~ bound (e.g. glass, rubber). Local charging.
Conductor connected to Earth: “grounded”.
Charging: contact, non contact, polarization
Coulomb’s law:
F = k |q1| |q2|/r2
k = (4pe0)-1 = 9 109 Nm2/C2
The charge of ~ 6.3 1018 electrons make -1 coulomb.
Superposition of electrical forces.
The electric field (E): due to one charged particle, due to a system
of charged particles, due to a continuous charge distribution (e.g. a
uniformly charged rod, ring, disk or sphere).
Field lines: density, direction, +ve ( or -ve) charges
Motion of a charged particle: F = qE = ma