41.Decibel is the unit used for

42.Mule is the hybrid of

43.Kilohertz is a unit which measures

44.What is the nature of motion of machine needle ?

45.Consider the following statements about a thermos flask : 1. It is a practical device in which the heat folowing into or out of the system by conduction, convection or radiation is reduced as much as possible. 2. It consists of a double - walled glass vessel. 3. The heat transfer by convection is minimised by silvering the surfaces and the radiation is minimised by evacuating the space between the walls.Of these, the correct ones are