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Choose the following statement a True of False. a. The real image formed by a lens is always inverted. b. The image formedby a lens is always inverted. c. The image formed by a concave lens is always erect and diminished. d. An air bubble insidewater acts likea concave lens. e. The distance between a real object and its real image formed by a single lens cannot be more than 4f. f. I an object is moved at a constant speed toward a convex lens from infinity to focus, then its image moves slower in the begninning and faster later on, away from the lens. g. The focal length of a glass (mu=1.5) lens is 10 cm in air. When it is completely immersed in water its focal length will become 40cm. |
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Answer» Solution : a. False. Real images of real object are always INVERTED. But for virtual object the image may be erect. b. False. Real images are always inverted. c. True. From equation, we have `m=(f_(0))/(x+f_(0))` The VALUE of mis always positive and less that 1. d. True . The air BUBBLE in water diverges a parallel beam of light.  E. True. The lease distance between a real object and its real image is 4f. f. True. `(1)/(y)+(1)/(x)=(1)/(f),(dx)/(dt)=-u, (dy)/(dt)=v` `-(1)/(y^(2))(dy)/(dt)-(1)/(x^(2))(dx)/(dt)=0` `v=(y^(2))/(x^(2))u` Initially, x is large and y is small. So, initially v is small. But as the object moves from `oo` to focus, x decreases and y increases. So, v also increases.  g. True. Using equation, we have `f=f_(0)[(mu(mu_(0)-1))/(mu_(0)-mu)]` Hence, `mu_(0)=(3)/(2), mu=(4)/(3)` `rArr f=4f_(0)` The effective FOCAL length comes out to be positive. |
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