Final answer:
The student appears to be asking about P.N. Rao but is likely referring to the discovery by Penzias and Wilson related to the Big Bang theory in 1970, or Rutherford's gold foil experiments beginning in 1909 that led to the nuclear model of the atom.
Step-by-step explanation:
The student's question seems to be confused about the identity of 'P.N. Rao' and the year of the experiment. However, the year 1970 is related to the Nobel Prize-winning discovery by Arno Penzias and Robert Wilson, who inadvertently observed the cosmic microwave background radiation. This was a foundational piece of evidence supporting the Big Bang theory.
When Ernest Rutherford started his gold foil experiment in 1909, it led to the rejection of the plum pudding model of the atom. Rutherford, along with his colleagues Hans Geiger and Ernest Marsden, bombarded gold foil with alpha particles and observed that some particles were deflected at large angles. This observation contradicted the plum pudding model, which couldn't explain such deflection if the atom was supposed to be a uniform sphere of positive charge with electrons inside.
Instead, Rutherford's experiment indicated that atoms have a small, dense, positively charged nucleus, with the rest of the atom being mostly empty space where the electrons are located. This conclusion was pivotal in the development of the nuclear model of the atom.