1.what do you understand by 1u or 1amu.

2.why is a bell provided with a big outer case?

1-An atomic mass unit (u) is a unit of mass used to express atomic and molecular weights. One atomic mass unit (1u) or 1 a.m.u. is defined as one twelfeth (1/12) of the mass of an atom of carbon-12.
 2-In a bell, a big outercase is used to increase the area for multiple reflection so that we can hear the sound clearly and sound is directed in forward direction.