Introduction to Health Physics: Fourth Edition - Ruang Baca FMIPA UB

REVIEW OF PHYSICAL PRINCIPLES 55
2.19. Two electrons are initially at rest, separated by 0.1 nm. After the electrons are
released, they repel each other. What is the kinetic energy of each electron when
they are 1.0-nm apart?
2.20. A cyclotron produces a 100-μA beam of 15-MeV deuterons. If the cyclotron
were 100% efficient in converting electrical energy into kinetic energy of the
deuterons, what is the minimum required power input, (in kilowatts)?
2.21. A1-μF capacitor is fully charged to 100 V by connecting it across the terminals
of a 100-V battery. The charged capacitor is then removed from the
battery and connected in parallel to an uncharged 2-μF capacitor as shown
below.
± ± ± ± ±
± ± ±
(a) What is the charge on each capacitor after the switch is closed?
(b) What is the voltage across the capacitors after the charge is redistributed?
2.22. (a) What voltage must be applied across two electrodes separated by 2-cm high
vacuum in order to have an electron starting from rest on the negative electrode
strike the positive plate in 10−8 s?
(b) With what speed will the electron strike the plate?
2.23. When hydrogen burns, it combines with oxygen according to
2H2 + O2 → 2H2O.
About 2.3 × 105 J of heat energy in the production of 1 mol of water. What is the
fractional reduction in the mass of the reactants in this reaction?
2.24. (a) A 1000-MW(e) nuclear power plant operates at a thermal efficiency of 33%
and at 75% capacity for 1 year. How many kilograms of nuclear fuel are
consumed during the year?
(b) If a coal-fired plant operates at the same efficiency and capacity factor, how
many kilograms coal must be burned during the year if the heat content of
the coal is 27 MJ/kg (11, 700 Btu/lb)?
2.25. The solar constant is defined as the rate at which solar radiant energy falls on
the earth’s atmosphere on a surface normal to the incident radiation. The mean
value for the solar constant is 1353 W/m2 , and the mean distance of the earth
from the sun is 1.5 × 108 km.
(a) At what rate is energy being emitted from the sun?
(b) At what rate, in metric tons per second, is the sun’s mass being converted
into energy?
2.26. What is the energy of a photon whose momentum is equal to that of a 10-MeV
electron?