Question

how do you know that nucleus is very small as compared to the size of atom explain with the help of Rutherford's model

Answer 1

actually Rutherford did an Alpha particle scattering experiment and after doing that experiment his observations were:-----
# most of the particles past straight without any deflection and as Alpha particle is positively charged so this shows that most of the space inside the atom is empty that's why it passes straight
# very few particles about deflected through small angles this shows that these those particles which passed near the positive body that's why due to repulsion from that positively charged body they get deviated from their path
#very few that is 1 out of 20000 deflected back so from these observations he concluded that ........
# as very less particles are deflected back it means the positively charged body is at very small place and that positively charged body was nucleus so in this way rutherford's model prove that nucleus is very small as compared to the size of atom

Answer 2

Rutherford observed that when alpha particles were bombarded on a very thin foil a very small portion of it bounced back, the portion being the nucleus which rebounded only 1 in 12000 rays.