Unformatted text preview: Physics 7C - Section 2 Fall Semester 2003 Second Midterm Exam (R. Marrus)
11/04/03 1) a)
b) C) 2) 4) A single slit 1 mm wide is uniformly illuminated by light of wavelength 2» = 589 nm.
A diffraction pattern is observed on a screen 3 m behind the slit. Throughout this
calculationyou may assume that the angles subtended at the slit are small. Find the distance between the first diffraction minima on each side of the central
maximum. The width of the slit is now doubled. Find: (I) The distance between the first
diffraction minima on each side of the central maximum. (11) The factor by which the
intensity of the central maximum changes. The slit is now illuminated with a second source of light of wavelength W. The value
of k’ is such that its second diffraction minimum on one side of the central maximum
coincides with the third diffraction minimum produced by light of wavelength 2».
Calculate N. In an inertial frame fixed relative to the earth, a red light suddenly ﬂashes at the origin and a white light suddenly ﬂashes at a point + 30 km from the origin. In the earth’s frame both ﬂashes are simultaneous. A spaceship moves with a speed v = 0.5c parallel to the line between the 2 points at which the ﬂashes occur. To an observer in the spaceship: What is the separation of the two lights? V: 0-5" C’— What is the time interval between ﬂashes? D Which ﬂash occurs first? __,_____________,____
O 6 30 K m An x-ray photon of wavelength 0.0021 nm is Compton scattered by a free electron (initially at rest) through an angle of 300 from the incident direction. Find the kinetic
energy in (eV) of the recoiling electron. Determine the radius of the star Procyon B from the following data: the ﬂux of
starlight reaching us is 1.7x10“2 watt/m2, the distance of the star is 11 light years, and
its’ surface temperature is 6600°K. Assume the star radiates like a blackbody. 5a) Light of frequency 1016 Hz is incident on a gas of hydrogen atoms in the ground state. What is the kinetic energy (in eV) of the emitted electrons? 5b) A hydrogen atom makes a transition from n=3 to n=2 and emits a photon. Calculate the energy of the recoiling nucleus. You may assume the recoil energy is small
compared to the photon energy. h= 6.62x10-34 joule-s = 4.14xioIS eV—s
c=3xlO8 m/sec. me(electron mass) = 9.1x10‘31 kg. = 51 lkeV/c2
Mp (proton mass) = 1.67x10'27 kg = 938 MeV/c2 leV = 1.6x10-19 joule e(electron charge) = 1.6x10‘19 coulomb
R(Rydberg constant) = 13.6eV k=1/(41te0) = 9x109 MKS
6 (Stefan—Boltzmann constant) = 5.67x10‘8 W/mz-s ...
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