YSP Modern Physics – Summer 2013
Homework set Q4 -- due 5 July
4.1: Compute binding energy per nucleon (in MeV) for
4
 2He
4.00153 amu

16

56
8O
15.991 amu
26Fe
235
92U
55.922 amu

234.995 amu
Describe the trend and explain its significance.
Needed numbers:
2
 1 amu =
 m(proton) =
 m(neutron)=
931.5 MeV/c
1.00782 amu
1.00867 amu
4.2 estimate the ratio of radii (give ratio relative to that of 11H) for
the following nuclei:
1
4.3
1H
12
6C
56
26Fe
208
82Pb
238
92U
Sun’s power output:
(a) Calculate Sun’s power output , assuming sun is a black body,
temp. = 5800K, radius 7 • 108m;
use Stefan-Boltzmann law
-8
4
-2 -4
P = A • σ • T σ = 5.670 • 10 W m K
(b) How much of this reaches Earth?
(assume distance Sun-Earth D=1.5x1011m)
(compare with Earth’s average power consumption of  20TW)
(c) Calculate the intensity (i.e. power per unit area) of e.m. radiation from the
Sun at the surface of the Earth at normal incidence (the “solar constant”).