Physics 123 – Sample Test #4
(After attempting these problems, click here for a key.)
 

1.  A fancy, relativistic sports car moves past an observer on a corner at a speed of 0.6 c.  The observer notices that it takes exactly 1.0 seconds for the driver of the car to shift from 56th gear to 57th gear.   From the driver's perspective, how long, in seconds, did it take to shift gears?

a.  0.6      b.  0.8       c.  1.0       d.  1.25       e.  1.67

2.  A spaceship moving past the earth with a speed of 0.8 c blasts the earth with pulsed laser photons every 10 seconds.  Observers on the earth see what time interval, in seconds, between the flashes?  (Assume that the ship is quite far away, shooting perpendicular to its direction of motion, so that a radial Doppler shift is not a necessary consideration.)

a.  13.4       b.  16.7       c.  12.5       d.  9.7       e. 6.0

3.  An electron (m_e = 9.11 × 10^-31 kg) has a speed of 0.5 c.  Determine the difference, in Joules, between its relativistic kinetic energy and its kinetic energy calculated without considering relativity.

a.  3.0 × 10^-15       b.   2.0 × 10^-15      c. 1.5 × 10^-15     d.  2.4 × 10^-15       e.  1.8 × 10^-15

4.  What is the maximum kinetic energy (in eV) of photoelectrons from a surface of work function 5.0 eV which is illuminated by photons of wavelength 400 nm?

a.  3.1       b.  -1.9       c. 1.9       d.  0.0       e.  1.2

5.  A solid state pulsed laser has an energy of 400 mJ per pulse.  If its wavelength is 1.06 μm, how many photons are in each pulse?
   

a.  2 × 10²⁵       b. 2 × 10²¹        c. 3 × 10¹⁸        d.  6 × 10³⁸       e.  2 × 10¹⁸

6.  An electron in a hydrogen atom makes a radiative transition from the n = 3 to the n = 1 energy state.  Determine the wavelength of the emitted photon (in nm).

a.  1006       b.  209       c.  306       d.  103       e.  821

7.  Find the binding energy of carbon-12 (in MeV), given that m_C = 11.996706 u, m_p = 1.007276 u, m_n = 1.008665 u, and u = 1.66 × 10^-27 kg.

a.  14.8       b.  0.5       c.  9.11      d.  92.4       e.  46.2

8.  A neutron is characterized by the term "thermal neutron" when

a.  its energy is of the order kT, where T is on the order of 0 °C.
b.  its energy is of the order kT, where T is on the order of 0 K.
c.  its energy is of the order kT, where T is on the order of 100°C.
d.  the neutron is warm. 

9.  What is the average kinetic energy (in keV) of ions that have a temperature of 10⁸ K?

a.  8       b.  13       c.  4       d.  16       e.  21

10.  One method to confine a plasma is with the use of

a.  electric fields       b.  magnetic fields       electromagnetic fields       d.  high temperature stainless steel       e.  laser beams