Cathode rays are negatively charged streams of particles arising from the cathode of an electric discharge tube at low pressure and high electric potential.

Any two properties of cathode rays are:

1. They are negatively charged particles so, they suffer deflection in electric and magnetic fields.
2. They travel with 1/10 of the velocity of light.

Following are the significance of Millikan's oil drop experiment:

1. It verifies that electronic charge is the smallest possible unit of charge.
2. It helps to calculate the electronic charge by using the value of the specific charge of electron (e/m).

Specific charge is the ratio of a particle's charge to its mass.

Since, the mass of an electron is about 1/1837 times that of the mass of a proton. Its mass is much smaller than the proton.

A positive ray contains alpha particles (doubly ionized He nucleus). Its mass is much larger than that of an electron so, the greater electronic charge has negligible effect as compared to its mass, and the specific charge is much smaller than that of the electrons.

No, it is not advised to perform Millikan's oil drop experiment with drops of any size due to limitations of experimental accuracy.

When we use a drop of larger size (as compared to microscopic sizes), they will have comparatively higher velocity which is difficult to detect.

Similarly, a large electric field should be applied to move the drop towards the positive terminal against gravity.