Atomic nuclei are made of protons and neutrons. this fact by itself shows thatthere must be some other type of force in addition to electrical and gravitationalforces. explain.

Protons and neutrons are packed together in a very small region called nucleus. Protons are positively charged and we know that like charges repel. Then how is it that protons are not repelling each other and flying away from nucleus?

You may think that gravitational force is holding all the protons together but it is not so. Gravitational force is many times weaker than repulsive force.

It is actually strong force which holds proton together. At this short distance, strong force comes into play and is several times stronger than the repulsive force.

there was no answer choices but i think its representative

convex lenses are thicker at the middle. rays of light that pass through the lens are brought closer together (they converge). a convex lens is a converging lens. when parallel rays of light pass through a convex lens the refracted rays converge at one point called the principal focus.