21 Transformer is not an amplifier because of

No power gain

22 The essential difference between an A.C dynamo and a D.C dynamo is that

A.C has slip rings but D.C has a commutator

23 Two objects that lose the same weight in water must have the same

Volume

24 The name of Madam Curie is associated with the discovery of

Radium

25 What is the speed of sound under normal conditions?

1100 feet per second (750 miles per hour)

26 Petrol and Diesel are the examples of

Potential energy

27 An allergy is

An excessive sensitiveness to some food or substances

28 Penicillin was discovered by

Alexander Fleming

29 When a body is thrown upwards, its velocity goes on

Decreasing

30 A rodent is an animal that has

Long sharp front teeth