Physics: E & M Flashcards
(42 cards)
Conductors
Silver, Copper, Aluminum, Iron, Mercury, Carbon, Water
Conductors
Silver, Copper, Aluminum, Iron, Mercury, Carbon, Water
Semiconductors
Germanium, Silicon
Insulators
Dry Air, Wood, Glass, Rubber
A positive charge is deposited on the left side of a metal sphere. Why does the positive charge distribute itself uniformly throughout the surface of the sphere?
Excess electrons from the rest of sphere are attracted to the excess protons
A rubber balloon possesses a positive charge. If brought near and touched to a wooden door, it sticks to the door. This does not occur with an uncharged balloon. The wooden door must be
a) electrically neutral
b) negatively charged
c) a conductor
d) lacking electrons
a) electrically neutral
Coulomb’s Law
F=kQq/r^2
see application of inverse square
Following Coulomb’s Law,
If force is decreased by a factor of 4. What happens to distance?
Increased by a factor of 2
Following Coulomb’s Law,
If force is increased by a factor of 9. What happens to distance?
Decreased by a factor of 3
Following Coulomb’s Law,
If distance is decreased by a factor of 10. What happens to force?
increased by a factor of 100
Following Coulomb’s Law,
If distance is increased by a factor of 5. What happens to force?
decreased by a factor of 25
What is true of the electrical potential energy (E) if charges are opposite?
E < 0
E is proportional to -1/r
What is true of the electrical potential energy (E) if charges are opposite?
E > 0
E is proportional to 1/r
Electric Potential
Conceptual Review:
(Volt = J/C)
• A charge Q produces an E and V around it uniformly
(E and V lines are perpendicular).
• The magnitude of E and V decrease as distance from Q increases.
• The magnitude of E and V produced by Q increases as
Q increases.
• An electric force exists only if a second charge is
placed in the electric field of Q.
• A system has electrical potential energy only if a
second charge is present.
What physics concepts
appliy the inverse square law
ie: X = 1/r^2
Force of Gravity
Force of Electrostatics
Intensity: power/area
I is proportional to 1/r^2
How do you change the energy of a wave
interference (constructive/destructive)
Units of spring constant k
N/m
Electric field (N/C)
E= F/q = (kQq/r^2)/q
E=kO/r^2
vector: curved lines that never intersect
Why can’t lines criss-cross in an electric field?
Cannot have 2 possible directions in one point in space
What does low density (spread out lines) in an electric field line
shows Weak field
Happens on outer part of field, bc E decreases as r increases (per inverse square law)
What can you tell about the spread and direction of arrows pointing in a field?
(Slide 10)
Negative charges point IN
Positive point out
MOre lines means higher density, means absolute value of Q is greater than a Q of few / more spread out lines
Potential Energy
F x d = kQq/r^2 x r = kQq/r
Semiconductors
Germanium, Silicon
Insulators
Dry Air, Wood, Glass, Rubber
