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Ashok0210

Asked: March 21, 2021In: Class 12 Physics

Answer the following questions: (a) Long distance radio broadcasts use short-wave bands. Why? (b) It is necessary to use satellites for long distance TV transmission. Why? (c) Optical and radio telescopes are built on the ground but X-ray astronomy is possible only from satellites orbiting the earth. Why? (d) The small ozone layer on top of the stratosphere is crucial for human survival. Why? (e) If the earth did not have an atmosphere, would its average surface temperature be higher or lower than what it is now? (e) Some scientists have predicted that a global nuclear war on the earth would be followed by a severe ‘nuclear winter’ with a devastating effect on life on earth. What might be the basis of this prediction?

Class 12 Physics CBSE and UP Board Electromagnetic Waves Chapter-8 Exercise 8.15 NCERT Solutions for Class 12 Physics Chapter 8 Question 15 Additional Exercise

Ashok0210

Asked: March 21, 2021In: Class 12 Physics

The image of a small electric bulb fixed on the wall of a room is to be obtained on the opposite wall 3 m away by means of a large convex lens. What is the maximum possible focal length of the lens required for the purpose?

Class 12 Physics CBSE and UP Board Ray Optics and Optical Instruments Chapter-9 Exercise 9.19 NCERT Solutions for Class 12 Physics Chapter 9 Question-19

Ashok0210

Asked: March 21, 2021In: Class 12 Physics

Answer the following questions: (a) You have learnt that plane and convex mirrors produce virtual images of objects. Can they produce real images under some circumstances? Explain. (b) A virtual image, we always say, cannot be caught on a screen. Yet when we ‘see’ a virtual image, we are obviously bringing it on to the ‘screen’ (i.e., the retina) of our eye. Is there a contradiction? (c) A diver under water, looks obliquely at a fisherman standing on the bank of a lake. Would the fisherman look taller or shorter to the diver than what he actually is? (d) Does the apparent depth of a tank of water change if viewed obliquely? If so, does the apparent depth increase or decrease? (e) The refractive index of diamond is much greater than that of ordinary glass. Is this fact of some use to a diamond cutter?

Class 12 Physics CBSE and UP Board Ray Optics and Optical Instruments Chapter-9 Exercise 9.18 NCERT Solutions for Class 12 Physics Chapter 9 Question-18

Ashok0210

Asked: March 21, 2021In: Class 12 Physics

(a) Figure 9.35 shows a cross-section of a ‘light pipe’ made of a glass fibre of refractive index 1.68. The outer covering of the pipe is made of a material of refractive index 1.44. What is the range of the angles of the incident rays with the axis of the pipe for which total reflections inside the pipe take place, as shown in the figure. (b) What is the answer if there is no outer covering of the pipe?

Class 12 Physics CBSE and UP Board Ray Optics and Optical Instruments Chapter-9 Exercise 9.17 NCERT Solutions for Class 12 Physics Chapter 9 Question-17

Ashok0210

Asked: March 21, 2021In: Class 12 Physics

A small pin fixed on a table top is viewed from above from a distance of 50 cm. By what distance would the pin appear to be raised if it is viewed from the same point through a 15 cm thick glass slab held parallel to the table? Refractive index of glass = 1.5. Does the answer depend on the location of the slab?

Class 12 Physics CBSE and UP Board Ray Optics and Optical Instruments Chapter-9 Exercise 9.16 NCERT Solutions for Class 12 Physics Chapter 9 Question-16

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The image of a small electric bulb fixed on the wall of a room is to be obtained on the opposite wall 3 m away by means of a large convex lens. What is the maximum possible focal length of the lens required for the purpose?

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