To clean the spectacles,people often breathe out on glasses to make them wet. Explain why do the glasses become wet.

A myopic person has been using spectacles of power -1.0 dioptre for distance vision. During old age he also needs to use separate reading glass of power +2.0 dioptres. Explain what may have happened.

Mercury does not wet the glass. Why?

Suppose the glass of the previous problem is covered by a jar and air inside the jar is completely pumped out a. What will be the answer to the problem? b.Show that the answers do not change if a glass of different shape is used provided the height, the bottom area and the volume are unchanged.

a. The top of the atmosphere is at about 400 kV with respectto the surface of the earth, corresponding to an electric field that decreases with altitude. Near the surface of the earth, the field is about 100 Vm^(-1). Why then do we not get a electric shock as we step out of our house into the openy (Assume the house to be a steel cage so there is no field inside!) b. A man fixes outside his house one evening a two metre high insulating slab carrying on its top a large aluminium sheet of area 1m^(2) . Will he get an electric shock if he touches the metal sheet next morning? c. The discharging current in the atmosphere due to the small conductivity of air is known to be 1800A on an average over the globe. Why then does the atmosphere not discharge itself completely in due course and become electrically neutral? In other words, what keeps the atmosphere charged? d. What are the forms of energy into which the electrical energy of the atmosphere is dissipated during a lightning? (Hint: The earth has an electric field of about 100 Vm^(-1) at its surface in the downward direction, corresponding to a surface charge density =-10^(-9) Cm^(-2) ?.

Why do we see water droplets on outer surface of a glass containing ice - cold water?

Read the passage and Answer the following question: In, vacuum the velocity of light radiation with different wavelength is the same. But in a material medium, the velocity of different colour radiations is not the same and they travel with different paths. Due to this, the refractive index of the medium is different for different colours. If white beam of light is incident on a glass prism, the angle of refraction for different colours is different. When Sunlight is incident on a refracting surface, then it gets split into seven coloured spectrum and emerges out. The splitting of light into its component colours is called dispersion. Sir Isaac Newton was the first to use a glass prism to obtain the spectrum of Sunlight. A glass prism is transparent medium bounded by two plane surfaces inclined at an angle. When white light is dispersed into seven colours by a prism, different colours of light bend through different angles with respect to incident ray. Out of these seven colours, red light bends the least, while violet light bends the most. So, the rays of each colour emerge along different paths and becomes distinct. Hence, we get spectrum of seven - different colours. Q. How do emergent rays appear ?

Read the passage and Answer the following question: In, vacuum the velocity of light radiation with different wavelength is the same. But in a material medium, the velocity of different colour radiations is not the same and they travel with different paths. Due to this, the refractive index of the medium is different for different colours. If white beam of light is incident on a glass prism, the angle of refraction for different colours is different. When Sunlight is incident on a refracting surface, then it gets split into seven coloured spectrum and emerges out. The splitting of light into its component colours is called dispersion. Sir Isaac Newton was the first to use a glass prism to obtain the spectrum of Sunlight. A glass prism is transparent medium bounded by two plane surfaces inclined at an angle. When white light is dispersed into seven colours by a prism, different colours of light bend through different angles with respect to incident ray. Out of these seven colours, red light bends the least, while violet light bends the most. So, the rays of each colour emerge along different paths and becomes distinct. Hence, we get spectrum of seven - different colours. Q. Write the colours of the Spectrum ?

Read the passage and answer the following question: In, vacuum the velocity of light radiation with different wavelength is the same. But in a material medium, the velocity of different colour radiations is not the same and they travel with different paths. Due to this, the refractive index of the medium is different for different colours. If white beam of light is incident on a glass prism, the angle of refraction for different colours is different. When Sunlight is incident on a refracting surface, then it gets split into seven coloured spectrum and emerges out. The splitting of light into its component colours is called dispersion. Sir Isaac Newton was the first to use a glass prism to obtain the spectrum of Sunlight. A glass prism is transparent medium bounded by two plane surfaces inclined at an angle. When white light is dispersed into seven colours by a prism, different colours of light bend through different angles with respect to incident ray. Out of these seven colours, red light bends the least, while violet light bends the most. So, the rays of each colour emerge along different paths and becomes distinct. Hence, we get spectrum of seven - different colours. Q. What is dispersion ?

Read the passage and Answer the following question: In, vacuum the velocity of light radiation with different wavelength is the same. But in a material medium, the velocity of different colour radiations is not the same and they travel with different paths. Due to this, the refractive index of the medium is different for different colours. If white beam of light is incident on a glass prism, the angle of refraction for different colours is different. When Sunlight is incident on a refracting surface, then it gets split into seven coloured spectrum and emerges out. The splitting of light into its component colours is called dispersion. Sir Isaac Newton was the first to use a glass prism to obtain the spectrum of Sunlight. A glass prism is transparent medium bounded by two plane surfaces inclined at an angle. When white light is dispersed into seven colours by a prism, different colours of light bend through different angles with respect to incident ray. Out of these seven colours, red light bends the least, while violet light bends the most. So, the rays of each colour emerge along different paths and becomes distinct. Hence, we get spectrum of seven - different colours. Q. What is spectrum ?