151: If a potato is placed on a pure paper plate which is white and unprinted and put in a microwave oven, the potato heats up but the paper plate does not. This is because:
(a) Potato contains water whereas paper does not contain water
(b) Potato transmits microwaves whereas paper reflects microwaves
(c) Potato is mainly made up of starch whereas paper is mainly made up of cellulose
(d) Potato is a fresh organic material whereas' paper is a dead organic material
Explanation:
Microwaves are a type of electromagnetic energy. Microwave ovens use this energy to cook foods. The microwaves are absorbed by water molecules in food and cause the water molecules to rotate more rapidly The extra energy of these more rapidly rotating water molecules spreads out and causes ther molecules to move more rapidly This causes the food to get warm and cook. Since the paper does not contain water molecules, it does not absorb the microwave energy.
Microwaves go through glass and paper without heating them. Metal objects reflect microwaves and will damage microwave ovens if placed in them. The walls of microwave ovens are metal to help reflect the microwaves back to the food to be cooked.
152: Haemophilia is a genetic disorder which leads to
(a) decrease in haemoglobin level
(b) rheumatic heart disease
(c) decrease in WBC
(d) non-clotting of blood
153: Consider the following statements about acetylene :
I. It is used in welding industry.
II. It is raw material for preparing plastics.
III. It is easily obtained by mixing silicon carbide and water.
Of these statements :
(a) I and II are correct
(b) I and III are correct
(c) II and III are correct
(d) I, II and III are correct
154: Assertion (A):
A diamond sparkles more than a glass imitation cut to the same shape.
Reason (R):
The refractive index of diamond is less than that of glass.
In the context of the above two statements, which one of the following is correct ?
(a) Both A and R are true, and R is the correct explanation of A
(b) Both A and R are true, but R is not a correct explanation of A
(c) A is true, but R is false
(d) A is false, but R is true
Explanation:
The refractive index (RI) of diamond (2.47) is much more than RI of Glass (1.57) hence the critical angle is very less in case of diamond compared to in glass. Thereby the light undergoes multiple total internal reflection in diamond makes the diamond sparkle (glitters).
155: Why DDT is banned in western countries?
(a) It remains in environment for a long time
(b) The insects are immunised
(c) It is a highly poisonous insecticide
(d) None of the above