Hello dear aspirant, 

There is a huge difference between these two courses.
B. Sc physical science with computer is a general course and it's cutoff is less than B. Sc Computer science Hons.
B. Sc physical science provides you an option of pursuing your post graduation in any of the three discipline whereas after B. Sc computer science you can pursue post graduation from computers only. You can also opt for MCA. The value of B. Sc computer science is higher than B. Sc physical science with computer science. For direct placements,  a company will prefer an honors student over a simple B. Sc student.

Yes there is a lot of difference between
1. BSC P.S. with CS and
2. BSC (CS) .
In the 1. Option you are going to study physics chemistry and CS as your subjects but if you opt the 2nd one  then your particular subjects will be related to CS only no other thing . It's like doing honors in any subject.
Hope you find it helpful.