Q 9.20 A screen is placed 90cm from an object. The image of the object on the screen is formed by a convex lens at two different locations separated by 20cm. Determine the focal length of the lens.
Q 9.19 The image of a small electric bulb fixed on the wall of a room is to be obtained on the opposite wall 3m away by means of a large convex lens. What is the maximum possible focal length of the lens required for the purpose?
Q 9.18 (e) Answer the following question:
The refractive index of diamond is much greater than that of ordinary glass. Is this fact of some use to a diamond cutter?
Q 9.18 (d) Answer the following question:
Does the apparent depth of a tank of water change if viewed obliquely? If so, does the apparent depth increase or decrease?
Q 9.18 (c) Answer the following question:
A diver underwater 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?
Q 9.18 (b) Answer the following question:
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?
Q 9.18 (a) Answer the following question:
You have learned that plane and convex mirrors produce virtual images of objects. Can they produce real images under some circumstances? Explain.
Q 9.17 (a) In the following figure 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.
Q 9.16 A small pin fixed on a table top is viewed from above from a distance of 50cm. By what distance would the pin appear to be raised if it is viewed from the same point through a 15cm thick glass slab held parallel to the table? Refractive index of glass = 1.5. Does the answer depend on the location of the slab?
Q 9.15 (d) Use the mirror equation to deduce that:
an object placed between the pole and focus of a concave mirror produces a virtual and enlarged image.
Q 9.15 (c) Use the mirror equation to deduce that:
the virtual image produced by a convex mirror is always diminished in size and is located between the focus and the pole.
Q. 9.15 (b) Use the mirror equation to deduce that:
a convex mirror always produces a virtual image independent of the location of the object.
Q 9.15 (a) Use the mirror equation to deduce that:
an object placed between f and 2f of a concave mirror produces a real image beyond 2f.
Q 9.14 (b) If this telescope is used to view the moon, what is the diameter of the image of the moon formed by the objective lens? The diameter of the moon is , and the radius of the lunar orbit is .
Q 9.14 (a) A giant refracting telescope at an observatory has an objective lens of focal length 15m. If an eyepiece of focal length 1.0cm is used, what is the angular magnification of the telescope?
Q 9.13 A small telescope has an objective lens of focal length 144cm and an eyepiece of focal length 6.0cm. What is the magnifying power of the telescope? What is the separation between the objective and the eyepiece?
Q 9.12 A person with a normal near point (25 cm) using a compound microscope with objective of focal length 8.0 mm and an eyepiece of focal length 2.5cm can bring an object placed at 9.0mm from the objective in sharp focus. What is the separation between the two lenses? Calculate the magnifying power of the microscope
Q 9.11 A compound microscope consists of an objective lens of focal length 2.0 cm and an eyepiece of focal length 6.25 cm separated by a distance of 15cm. How far from the objective should an object be placed in order to obtain the final image at (a) the least distance of distinct vision (25cm), and (b) at infinity? What is the magnifying power of the microscope in each case?
Q 9.10 What is the focal length of a convex lens of focal length 30cm in contact with a concave lens of focal length 20cm? Is the system a converging or a diverging lens? Ignore the thickness of the lenses.