Upload
alice-harris
View
228
Download
6
Embed Size (px)
Citation preview
Electrostatics
• Two types of electric charge:– Negative (excess electrons)– Positive (lacking electrons)
• e = elementary unit of charge
= magnitude of charge on an electron
= 1.60 x 10-19 Coulomb
Types of materials
• Conductors: electric charges move freely (ex. Metals)
• Insulators: Electric charges do not move freely (ex. Plastic, rubber, glass, etc)
• Semiconductors: Mix of conductor and insulator properties (silicon)
• Superconductors: electric charges move without resistance.
Particle Mass Electric Charge
Electron me=9.110x10-31 kg q=-e
q=-1.60x10-19 C
Proton mp=1.673x10-27 kg q=+e
q=+1.60x10-19 C
Neutron mn=1.675x10-27 kg q=0
q=0 C
Coulombs Law
The electric force between two point charges is directly proportional to the product of the two charges and inversely proportional to the square of the distance between them, and directed by the line joining the two charges.
€
Fe =kq1q2
r2
Electric force
Charge 1
Charge 2
Radius
8.99 x 109 N m2 C-2
Determine the force on q1, as shown above
Electric field
• A region in space surrounding a charged object in which a second charged object experiences an electrical force.
• Similar to gravitational field around a planet…but the mass is smaller and the force is stronger
Diagram symbols
+ charged sphere
+ point charge
- point charge
Rules of electric field lines
1. Lines never cross2. Show the direction of force on a small
positive test charge3. Out of positive, toward negative4. Direction of electric field is tangent to field
lines5. Density of field lines is proportional to field
strength (density=intensity)6. Perpendicular to surface
Draw the field lines, assuming +1 and -1
Calculating
eFEq
= eF Eq=
Electric Field
Force
Charge
Electric Field
€
E =k
r2
q=k
Q
r2
Charge creating the field
Charge affected by the field
Electric fieldradius
€
E =kQ
r2eFEq
=eF Eq=
€
Fe =kq1q2
r2k = 8.99 x 109 N m2 C-2
Summary