Did you feel anything difficult in Physics Board paper of 2018. It is not SO! Actually we are used to study based on Question papers rather than concept. It could be the reason for feeling the paper tough.
Secondly we at times neglect NCERT. It is true that NCERT language sometimes is very BORING and irritating. But you have to keep in MIND the paper making authority do uses the TEXT of this BOOK only.
Common confusion were:
Q. Which mode of propagation is used by short wave broad cast ?
A. It is already stated in NCERT Page 520. Text I am rewriting here .
In the frequency range from a few MHz up to 30 to 40 MHz, long distance communication can be achieved by ionospheric reflection of radio waves back towards the earth. This mode of propagation is called sky wave propagation and is used by short wave broadcast services. The ionosphere
is so called because of the presence of a large number of ions or charged particles. It extends from a height of ~ 65 Km to about 400 Km above the earth’s surface
Q. Name the electromagnetic radiation used used for (i) water purifiers (ii) Eye surgery
Now surprisingly both the parts had same answer, but somehow whenever such questions come we feel it should have two different answers.
A. It is again from TEXT of NCERT . Page 282 Text is being re written here.
Welders wear special glass goggles or face masks with glass windows to protect their eyes from large amount of UV produced by welding arcs. Due to its shorter wavelengths, UV radiations can be focussed into very narrow beams for high precision applications such as LASIK (Laserassisted
in situ keratomileusis) eye surgery. UV lamps are used to kill germs in water purifiers.
ahve already stated many times that Communication Chapter and EM wave chapter, you must READ NCERT as a holy book.
Q. A symmetric biconvex lens of radius of curvature R and made of glass of refractive index 1.5, is placed on a layer of liquid placed on top of a plane mirror as shown in figure. An optical needle with its tip on the principal axis of the lens is moved along the axis until its real, inverted image coincides with lens itself. On removing the liquid layer and repeating the experiment, the distance is found to be y. Obtain the expression of refractive index of material in terms of x and y
A. Here again it is similar to Problem 9.38 , Last question of NCERT Ray Optics .
Please find solution in video.