Physics 202' Review Session for Exam3

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Physics 202. Review Session for Exam3

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Quizzes/Exercises Determine Direction Of emf

• Indicate the direction of emf in the following
  cases

. . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . .






B
B increases
B decreases
B decreases
. . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . .


B
path outside B
B increases
B decreases
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Faradays Law (Reminder)

• The emf induced in a circuit is proportional to
  the time rate of change of magnetic flux through
  the circuit.
• Notes
• Circuit any closed path
• does not have to be
• real conducting circuit
• The path/circuit does not
• have to be circular, or even planar

nominal direction of e
B
q
A
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Methods to Change Electric Flux

• Change of FB? emf
• To change FB
• Change B ? emf produced by an induced E field
• Change A ? motional emf
• Change ? ? motional emf
• Combination of above

Electric Generators
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Exercise Calculate Inductance of a Solenoid
Area A

• show that for an ideal solenoid
• (see board)

of turns N
Reminder magnetic field inside the solenoid
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Energy in an Inductor

• Energy stored in an inductor is U ½ LI2
• This energy is stored in the form of magnetic
  field energy density uB ½ B2/m0 (recall
  uE ½ e0E2)
• Compare
• Inductor energy stored U ½ LI2
• Capacitor energy stored U ½ C(DV)2
• Resistor no energy stored, (all energy
  converted to heat)

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Basic Circuit Components
e
r
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Turn on LR Circuit
Note the time constant is tL/R
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Turn off LR Circuit
Note the time constant is tL/R
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Charging a Capacitor in RC Circuit
Note tºRC is called time constant
Charging
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Discharging a Capacitor in RC Circuit
Note the time constant tRC
discharging
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Energy Stored in a LC Circuit

• Reminder Energy stored in
• Inductor energy stored UL ½ LI2
• Capacitor energy stored UC ½ C(DV)2 ½ Q2/C

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Current And Voltages in a Series RLC Circuit
DvR(DVR)max Sin(wt) DvL(DVL)max Sin(wt
p/2) DvC(DVC)max Sin(wt - p/2)
i Imax Sin(wt)
DVmax Sin(wt f)
Quiz Can the voltage amplitudes across each
components , (DVR)max , (DVL)max , (DVC)max
larger than the overall voltage amplitude DVmax ?
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Summary of Impedances and Phases
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Electromagnetic Waves

• EM wave equations
• Plane wave solutions
• E Emaxsin(kx-wtf) B Bmaxsin(kx-wtf)
  
• Properties
• No medium is necessary.
• E and B are normal to each other
• E and B are in phase
• Direction of wave is normal to both E and B
• (EM waves are transverse waves)
• Speed of EM wave
• E/B Emax/Bmaxc
• Transverse wave two polarizations possible

Well have quizzes about EM waves, including the
Poynting vector
same f, set to be 0
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Momentum Carried By EM Waves

• EM waves momentum energy/c
• Radiation Pressure (P)

100 absorption
100 reflection
Dp p ? P S/c
Dp 2p ? P 2S/c
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Wavelength and Frequency

• Because of the wave equation the wavelength of
  and frequency of a EM wave in vacuum are related
  by
• Example Determine the wavelength of an EM wave
  of frequency 50 MHz in free space

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Example Solar Energy

• The average intensity of the EM radiation from
  the Sun on Earth is S 103 W/m2
• What is the average radiation pressure for 100
  absorption
• What is the force exerted by EM radiation by the
  Sun on a surface of 1 m2

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Example Solar Energy (cont)

• The average intensity of the EM radiation from
  the Sun on Earth is S 103 W/m2
• What is the average radiation pressure for 50
  absorption and 50 reflection