Winter wk 1 – Tues.4.Jan.05
•
•
•
•
Tsunami workshop
Earth Part 3: Weather
Physics Ch.21: Electric charge
Physics Ch.22: Electric fields
Energy Systems, EJZ
Earth, Part 3: Weather & Climate
Weather is powered by Sun (79-82)
Low pressure = bad weather, rotates CCW in N
Jet stream carries weather across US (p.72-73)
Heat, moisture, and wind provide weather energy
Temperature drops with altitude (in troposphere):
air condenses or freezes, and precipitates (83)
Cooling water in air releases heat to surroundings
Winds
Climate
Climate = aggregate weather: averaged over
space and time: Temp and Precipitation
Depends on Sun, land covers, and longer-term
interaction between land, atmosphere, and
oceans
Recent examples of climate change:
• 12,000 yrs ago – emergence from ice age
• Medieval Maximum (1100s) more solar
activity, drought in SW ruined Chaco culture
• Maunder Minimum (late 1600s) few
sunspots, frozen N Europe, famine & plague
Physics Ch.21: Electric Charge
21-3: Conductors and insulators:
Checkpoint 1, #4
21-4: Coulomb’s Law (#2)
Compare Felectrostatic to Fgravity (#65)
21-5: Charge is quantized (#24-26)
21-6: Charge is conserved (#30)
Current = rate of flow of charge
(lightning #54, defibrillator
#56)
Charge, conductors, insulators
21-3: Conductors and insulators: Checkpoint 1
Coulomb’s law
21-4: Coulomb’s Law (#2)
qQ
1 qQ
FE  k 2 rˆ 
rˆ
2
r
4 0 r
Compare Felectrostatic to Fgravity (#65)
mM
FG  G 2 rˆ
r
21-5: Charge is quantized (#24-26)
21-6: Charge is conserved (#30) Is e=e- or e+?
(a) p  n + e•
(b) n  p + e•
Current = rate of flow of charge
Current = rate of flow of charge (defibrillator #56)
#54: In the return stroke of a typical lightning
bolt, a current of I=2.5 x 104 A exists for
t=20 ms. How much charge is transferred in
this event?
Current = charge/time
Charge Q =
I = Q/t
Physics Ch.22: Electric Field
22-3: Electric field E maps the
direction and strength of the
force F (Q1, #1, 2)
22-4: Field due to a point charge
(Q2, 5, #4, 11, )
22-8: Point charge can be
accelerated by an electric
field (Q8, #38, 39, 49)
Compare to gravity: #75, 85 (42)
E field maps electric force
22-3: Electric field E maps the direction and
strength of the force F (Q1, #1, 2)
Field due to a point charge
22-4: Field due to a point charge (Q2, 5, #4, 11, )
If the Earth’s electric field is 150 N/C near the
surface, what is the charge Q on the Earth?
What is the charge density (s=Q/area)?
22-8 E field can accelerate charges
Q8, #38, 39, 49
Compare E to gravity: #75, 85 (42) A spherical
water droplet is suspended in a cloud with E=462 N/C
(a) What is Fg on the drop?
(b) How many excess electrons does it have?