Class Test I - 12th February, 2004

total marks - 25, time - 40 minutes



  1. Which band of astronomy is most affected by the use of mobile phones? [2]
  2. In which band of astronomy have we achieved the maximum spatial resolution? [2]
  3. $\lambda=21$ cm is a signature of the HII regions. What is this due to? [2]
  4. $H_0 \sim 100 km s^{-1} Mpc^{-1}$. What is the largest length-scale of the present universe? [2]
  5. The luminosity of the Sun is $\sim 10^{33} erg/s$. Estimate the mass loss per year. [2]
  6. Estimate the Schwarzschild radius of a a $10^3$M$_{\odot}$ Black Hole. [2.5]
  7. Estimate the absolute maximum of the magnetic field that can be present in a neutron star ( $M = 1.4\mbox{{\rm M}$_{\odot}$}, R = 10km$). [2.5]
  8. Estimate the surface gravity of a White Dwarf ( $M= 1.4\mbox{{\rm M}$_{\odot}$}, R = 10^4km$). What would be the tidal force on a human being ($m=60kg, L=2m$) there? [5]
  9. Estimate the density at which a non-interacting gas of electrons would become relativistic? (Assume the ratio of electrons to nucleons to be 1:2.) [5]

Physical & Astrophysical Data :


$\displaystyle c$ $\textstyle =$ $\displaystyle 3 \times 10^{10} cm s^{-1}$  
$\displaystyle G$ $\textstyle =$ $\displaystyle 6.6732 \times 10^{-8} cgs$  
$\displaystyle \hbar$ $\textstyle =$ $\displaystyle 1.0546 \times 10^{-27} cgs$  
$\displaystyle m_p$ $\textstyle =$ $\displaystyle 1.6726 \times 10^{-24} gm$  
$\displaystyle m_e$ $\textstyle =$ $\displaystyle 9.1095 \times 10^{-28} gm$  
$\displaystyle \mbox{{\rm M}$_{\odot}$}$ $\textstyle =$ $\displaystyle 1.989 \times 10^{33} gm$  
$\displaystyle e$ $\textstyle =$ $\displaystyle 4.8032 \times 10^{-10} cgs$  

Special Instruction : Calculators are not to be used.


Sushan Konar 2004-02-12