The yellow colour has a greater luminous efficiency as compared to the other colours. Can we increase the illuminating power of a white light source by putting a yellow plastic paper around this source ?

You are given four sources of light each on providing a light of a single colour - red, blue green and yellow. Suppose the angle o refraction for a beam of yellow ligh corresponding to a particular angle o incidence at the interface of two media is 90° Which of the following statements is correct i the source of yellow light is replaced with tha of other lights without changing the angle o incidence ?

A bag contains a red ball, a black ball, a yellow ball and a white ball. One ball is selected randomly and note its colour and then put it into the bag. Again second ball is selected and note its colour. Write the sample space for this experiment. Hence, describe the following events : (1) A: Selected both the balls are of same colours. (2) B: Only one ball is white. (3) C: At least one ball is white. (4) D: Both the balls are of different colour. Hence, find AnnB,BuuC,AuuD,AnnD . What can we say about the events B and C ? What can we say about the events A and D?

An electron microscope uses electrons accelerated by a voltage of 50 kV. Determine the de Broglie wavelength associated with the electrons. If other factors (such as numerical aperture, etc.) are taken to be roughly the same, how does the resolving power of an electron microscope compare with that of an optical microscope which uses yellow light?

To check the pH of tap water and compare it with pH of the water in the local water body. Apparatus : Test tubes or beaker Materials : Universal pH indicator / litmus paper Procedure : implies Take water sample from tap of your home in a test tube. implies Add few drops of the universal indicator into the test tube containing tap water. implies Observe the water sample in the test tube for colour change. implies Test pH using a litmus paper, in the water sample placed in a beaker. implies Dip the litmus paper into the water in the local water body. implies Observe colour changes of the litmus paper. Observation : implies Test tube containing tap water, turns yellow colour with addition of pH indicator. implies Litmus paper does not show colour change with tap water. implies Water sample collected from pond shows red colour with pH indicator. Litmus paper turns red as it is dipped in water of local water body. Conclusion : The uncontaminated tap water is neutral while water of local water body is acidic. Can you say whether the water is polluted or not on the basis of your observations?

To check the pH of tap water and compare it with pH of the water in the local water body. Apparatus : Test tubes or beaker Materials : Universal pH indicator / litmus paper Procedure : implies Take water sample from tap of your home in a test tube. implies Add few drops of the universal indicator into the test tube containing tap water. implies Observe the water sample in the test tube for colour change. implies Test pH using a litmus paper, in the water sample placed in a beaker. implies Dip the litmus paper into the water in the local water body. implies Observe colour changes of the litmus paper. Observation : implies Test tube containing tap water, turns yellow colour with addition of pH indicator. implies Litmus paper does not show colour change with tap water. implies Water sample collected from pond shows red colour with pH indicator. Litmus paper turns red as it is dipped in water of local water body. Conclusion : The uncontaminated tap water is neutral while water of local water body is acidic. Can aquatic life survive in acidic water of water body?

To check the pH of tap water and compare it with pH of the water in the local water body. Apparatus : Test tubes or beaker Materials : Universal pH indicator / litmus paper Procedure : implies Take water sample from tap of your home in a test tube. implies Add few drops of the universal indicator into the test tube containing tap water. implies Observe the water sample in the test tube for colour change. implies Test pH using a litmus paper, in the water sample placed in a beaker. implies Dip the litmus paper into the water in the local water body. implies Observe colour changes of the litmus paper. Observation : implies Test tube containing tap water, turns yellow colour with addition of pH indicator. implies Litmus paper does not show colour change with tap water. implies Water sample collected from pond shows red colour with pH indicator. Litmus paper turns red as it is dipped in water of local water body. Conclusion : The uncontaminated tap water is neutral while water of local water body is acidic. What is the cause for acidic water in water body?

Science, like any knowledge, can be put to good or bad use, depending on the user. Given below are some of the applications of science. Formulate your views on whether the particular application is good, bad or something that cannot be so clearly categorised : (a) Mass vaccination against small pox to curb and finally eradicate this disease from the population. (This has already been successfully done in India). (b) Television for eradication of illiteracy and for mass communication of news and ideas. (c) Prenatal sex determination (d) Computers for increase in work efficiency (e) Putting artificial satellites into orbits around the Earth (f ) Development of nuclear weapons (g) Development of new and powerful techniques of chemical and biological warfare). (h) Purification of water for drinking (i) Plastic surgery (j ) Cloning

The wavelength of light in the visible region is about 390 nm for violet colour ,about 550 nm (average wavelength) for yellow-green colour and about 760 nm for red colour. (a)What are the energies of photons in (eV) at the (i) violet end, (ii)average wavelength,yellow-green colour,and (iii) red end of the visible spectrum ? (Take h =6.63xx110^(-34)) js and 1 eV= 1.6xx10^(-19) J). (b)From which of the photosensitive material with work functions listed n Table 11.1 and using the results of (i),(ii) and (iii) of (a), can you build a photoelectric device that operates with visible light?