Explain why the clear sky appears blue to a person on the surface of the earth and dark instead of blue to the passengers flying at very high altitudes.

Why does clear sky appear blue ?

The clear sky appears blue, because

Why does the sky appear dark instead of blue to an astronaut?

The sky would appear red instead of blue if

Explain, why in daylight an object appears red when seen through a red glass and black when seen through a blue glass?

An experimental setup of verification of photoelectric effect is shown in the diagram. The voltage across the electrode is measured with the help of an ideal voltmetar, and which can be varied by moving jockey 'J' on the potentiometer wire. The battery used in potentiometer circuit is of 20 V and its internal resistance is 2omega . The resistance of 100 cm long potentiometer wire is 8 omega . The photo current is measured with the help of an ideal ammeter. Two plates of potassium oxide of area 50 cm^(2) at separation 0.5 mm are used in the vacuum tube. Photo current in the circuit is very small so we can treat potentiometer circuit an indepdent circuit. The wavelength of various colours is as follows : |{:("Light",underset("Violet")(1),underset("Blue")(2),underset("Green")(3),underset("Yellow")(4),underset("Orange")(5),underset("Red")(6)),(lambda "in" Årarr,4000-4500,4500-5000,5000-5500,5500-6000,6000-6500,6500-7000):}| The number of electrons appeared on the surface of the cathode plate, when the jockey is connected at the ened 'P' of the potentiometer wire. Assume that no radiation is falling on the plates.

The set up shown alongside was kept in sunlight for an hour. It was observed that drops of water appeared on the inside surface of the polythene bag (a) Name the process which is being demonstrated. (b) Why was the pot with its soil left uncovered by the polythene bag ? (c ) Why was the pot left in sunlight? (d) Suppose that the pot in this experimetn was placed inside a dark room instead of placeing it in sunlight for some time. What difference would be noticed? ……………………………….

What is scattering of light? Use this phenomenon to explain why (i) the Sun appears reddish at sum-rise, and (ii) the clear sky appears blue.

A hydrated mettalic salt(A). Light green in colour , on careful heating gives a white anhydrates residue (B),(B) is soluble in water and its aqueous gives a dark blue precipitate ( C ) with potassium hexacyanidoferrate (III) . (B ) on strong heating gives a brown residue(D) and a mixture of two gases(E ) and (F ). The gaseous mixture when passed through acidified potassium dichromate , produce green colour solution and when passed through lead acetate solution gave a white precipitate. Out of two gase( E) can act as both reducing as well as oxidising agent. Identify (A) ,(B) ,(C ),(D) , and (F) and gives the reaction involved. Explain why salt(A) become white on heating .

Explain the following observation: a. Lyphilic colloid is more stable than lyophobic colloid. b. Coagulation takes place when sodium chloride solution is added to a colloidal solution of ferric hydroxide. c. Sky appears blue in colour.