3. In our class demo, we used three pipes of the same length, one plastic, one metallic and one metallic but with a gap. When we dropped a small magnet through those pipes, the times for the magnet to reach the end of the pipes were different. (a) State what the differences are and (b) explain these differences. Write down your answers on the answer sheet only. 4. In a normal sunny day, the sky is blue but the cloud is normally white. Explain in detail why the sky is blue but the cloud is normally white. Write down your answers on the answer sheet only. Solution 3 a) The difference lies in the conductivity and the induced current produced due to motion of magnet. b) Plastic pipe is a non conductor of electricity, so no induced current is produced.Therefore magnet passes through it the fastest (in least time). Metallic pipe has induced current which opposes the motion of magnet in accordance with lenz law.So magnet slows down a bit while passing through it. Metallic pipe with a gap also has induced current but less than that produced in pipe without gap.So magnet passes through it a bit faster than that in other metallic pipe. Order of times of passage: Metallic pipe without gap > Metallic pipe with gap>Plastic pipe 4. The blue colour of sky and white colour of clouds in is principally due to scattering of light by particles in atmosphere and clouds. As for sky, much of the ultraviolet light of sun is absorbed by atmosphere.Remaining part which passes through is scattered by particles in atmosphere.In accordance with Rayleigh scattering, violet is most scattered followed by blue , green, yellow, orange and red.Even though violet is most scattered but human eye isn\'t very sensitive to it rather it responds to second most scattered light blue.So sky appears blue to human eye. As for white colour of clouds, the cloud particles are much bigger than the atmospheric ones.So the bigger cloud particles scatter the light of different wavelengths equally.As a consequence of this , all equally scattered wavelengths merge to impart clouds the white colour. .