Physics 1C



Physics 1C Week 7 Questions Fall 1998

1. One of the mirrors of a Michelson interferometer is moved and 426 fringe pairs pass the centre point of the viewing telescope. The instrument is illuminated with 632.8 nm wavelength light from a He-Ne laser. How far was it moved?

2. A slit of width 10(m is illuminated with light of ( = 632.8 nm. Find the angular position of the first diffraction minimum.

3. Light from a sodium lamp has two strong yellow components at 589.5923 nm and 588.9953 nm. How far apart in the first-order spectrum will these two be on a screen 1.00 m from a grating having 10,000 lines/cm?

4. An electron of rest energy 511 keV is accelerated through 60kV in a HDTV set. Find its:

a) total energy E

b) momentum P

c) speed v

d) mass m, measured by an observer at rest

5. An alpha particle with a kinetic energy of 4.05 MeV is fired directly at a Ge32 nucleus. How close does it get?

Physics 1C Week 7 Solutions Fall 1998

1. The path difference increases by ( for every (/2 moved by our mirror and results in one fringe passage. Thus, (x = N((/2) = 426/2 (632.8 nm) = 0.135 mm.

2. Minima occur at asin( = m(, n = 1, 2, 3, …

At the first minimum m = 1

Solve for (, sin( = [pic],

( = arc sin [pic] = arc sin [pic]= 3.628 o

3. y1 = s(1/a, y2 = s(2/a, y1 - y2 = (589.5923 - 588.9953)(10-9)(1.00 m)/(10-6) = 0.597 mm. Using s = 1m and a = 10-4 cm = 10-6 m.

4. (a) E = 511 + 60 = 571 keV

(b) [pic]

[pic] keV/c

(c) [pic]

[pic] hence [pic] c

(d) [pic] keV/c2

5.

At closest approach, initial KE = work done = PE = [pic] [pic]

x [pic]

-----------------------

(

a

(x

N[pic]

(( = N(

• [pic]

• [pic]

•

( particle

KE = 0

at closest approach

KE = 4.05 MeV

x

Ge32

nucleus

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