(a) Why do see better through the corner of our eye in darkness?
(b) How can you show that the olfactory receptors are quickly fatigued?

(a) Why have primary amines higher boiling point than tertiary amines? (b) How can you find out whether a given amine is a primary amine? Write the chemical reaction involved in the test you perform.

(a)How could you use a borometer to measure the height of a mountain pass? (b) Why can water not be sucked to a height greater than 10 m even with a good suction pump?

(a) When we put our ear to a railway line, we can hear the sound of an approaching train even when the train is far off but its sound cannot be heared through the air. Why? (b) How could you convince a small child that when you speak, it is not necessary for air to travel from your mouth to the ear of a listener?

A student claims that because of atmospheric refraction, the sun can be seen after it has set, and the day is, therefore, longer than if the earth had no atmosphere. (a) What does the student mean by saying that the sun can be see after it has set ? (b) Do you think that the students' conclusion is correct ?

(a) Draw a circuit diagram showing two lamps, one cell and a switch connected in series. (b) How can you change the brightness of the lamps?