Why should a fuse with defined rating not be replaced by one with a larger rating?

The magnetic field produced by a current carrying conductor is shown below. Is there a similar magnetic field produced around a thin beam of moving α-particles and neutrons? Justify your answer.

What do you understand by the following statements?

(a) The heat capacity of the body is 60 JK^-1.

(b) The specific heat capacity of lead is 130 Jkg^-1K^-1