Transcript win1Tues
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?