import math
# Variables
T_c = 4.2; #critical temperature of mercury
k = 1.4*10**(-23); #
e = 1.6*10**(-19); #charge on the electron
# Calculation
E_g = 3*k*T_c; #energy gap (in Joule)
E = E_g/e; #energy gap (in electron volt)
h = 6.6*10**(-34) # in J-s
c = 3*10**8; #in m/s
wavelength = h*c/E_g; #wavelength of a photon (in m)
# Results
print 'energy gap = %.1e ev'%E
print 'wavelength of a photon = %.1e m'%wavelength