Download Winter wk 3 – Thus.20.Jan.05

yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts

Magnetohydrodynamics wikipedia, lookup

Eddy current wikipedia, lookup

Electric charge wikipedia, lookup

Superconductivity wikipedia, lookup

Scanning SQUID microscope wikipedia, lookup

Photovoltaics wikipedia, lookup

Wireless power transfer wikipedia, lookup

Electroactive polymers wikipedia, lookup

Electromagnetism wikipedia, lookup

Aurora wikipedia, lookup

Static electricity wikipedia, lookup

Hall effect wikipedia, lookup

History of electromagnetic theory wikipedia, lookup

Electric machine wikipedia, lookup

Geomagnetic storm wikipedia, lookup

Electrification wikipedia, lookup

Electrical resistivity and conductivity wikipedia, lookup

General Electric wikipedia, lookup

Earthing system wikipedia, lookup

History of electric power transmission wikipedia, lookup

Insulator (electricity) wikipedia, lookup

Electrostatics wikipedia, lookup

Opto-isolator wikipedia, lookup

Stray voltage wikipedia, lookup

Electric current wikipedia, lookup

History of electrochemistry wikipedia, lookup

Mains electricity wikipedia, lookup

Ohm's law wikipedia, lookup

Electricity wikipedia, lookup

Electrical resistance and conductance wikipedia, lookup

Electromotive force wikipedia, lookup

Alternating current wikipedia, lookup

High voltage wikipedia, lookup

Winter wk 3 – Thus.20.Jan.05
Ch.24: Voltage and electric field
Ch.26: Current and resistance
Solar applications
Ch.27: Circuits
Energy Systems, EJZ
Equipotential surfaces and E fields
Equipotential = constant voltage
Conductors are equipotentials, in electrostatics
Potential difference  Electric field
dV/dx = -E or, equivalently, V    E  dr
Practice: Ch.24 Q5,8 (p.646), P#3, 4, 6, 35
Ch.24 #4
Ch.24 #6
Ch.24 #35
Electrostatics (d/dt=0):
charges  fields  forces, energy
 E.dA = q/0=, E = F/q
V (r ) 
 (r ' )
4  
 
d '    E  dl
E   V
W = qV, C = q/V
• Charges make E fields
and forces
• charges make scalar
potential differences
• E can be found from V
• Electric forces move
• Electric fields store
energy (capacitance)
Ch.26: Currents and Resistance
Current = rate of flow of charge
I = dq/dt
Units: amps = coulombs/sec
Current density: J = current/area = n e v
Ch.26 Q1, 2, P.1, 8
Water flow:
Electricity flow:
voltage V
current I
Ch.26: Q1, 2, P.1, 8
Resistance = resistivity * area/length
R =  * A/L
Which conductor has the greatest resistivity?
Ch.26: Q3
Ohm’s law
In many substances, for a given resistance R,
the stronger the driving voltage, the greater
the current that flows:
Voltage = current * resistance
Ch.26 Q5, P.17
Power in electric circuits
Power = rate of energy xfr = voltage*current
units: Watts = volts * amps
Recall that work = qV. Units: J = CV
Solve for V(J,C) =
Then [volts]*[amps] = ____*C/s = ______
If V=IR, find P(I,R) =
Ch.26 #35, 64
P(R,V) =
Ch.27: Circuits:
Battery pumps electricity  current flows
Voltage = emf
Voltage = potential difference
Electromotive force  = V = dW/dq =work
done per unit charge
d/dx = -E = electric field
Emf  and electric field E
d/dx = -E = electric field
Using the fundamental theorem of calculus,
we can derive another of Maxwell’s eqns:
 E
 dx dx   E dx
    E dx
Ch.27: Practice with simple circuits
#5, 14
Solar applications
Storms from the Sun:
p.13: If a CME travels at 1 million miles per hour, how
long does it take to reach Earth?
p.16: The 2 May 1994 event dumped 4600 GW-hr of
electricity into Earth’s upper atmosphere. How much
energy is that in Joules?
p.16: If the Earth’s mean magnetic field is B0=0.5 Gauss,
and one Tesla=104 Gauss, by what percent does 2000
nanoTesla change Earth’s field?
p.54: For the CME of 1 Sept 1859: calculate its speed v,
if it took 18 hours to reach Earth.
more Solar applications
Storms from the Sun:
p.77: If Rsun = 100 REarth, then find the ratio of their
volumes, Vsun/VEarth
p.77: If m=5 millions tons of mass is converted to energy
(E=mc2) each second, calculate the power (P) produced
by the Sun.
p.82: If the Sun’s mass is M=2x1030 kg, and it keeps
losing dm/dt = 5 million tons per second, how long (T)
can the Sun last?
p.83: If the solar wind pours I=1 million amps into Earths
magnetosphere, how much charge (Q) is that per day?
Extra solar applications
p.13: Calculate vthermal from Tsolar wind. Compare to vflow.
p.16: Derive the altitude for a geosynchronous orbit
p.77: If the Sun’s core temperature is about T=107K,
calculate the thermal speed vth of protons in the core.