i need some help in this conceptual questions..?

Question

1)a beacon in lighthouse is to produce a parallel beam of light. The beacon consists of bulb be placed outside the focal point, at the focal point or inside the focal point of lense? State ur reason.

2)two people who were glasses were camping. One is near sighted and the other is farsighted. Whose glasses may be useful in a starting a fire with sun rays? Give ur reasoning

3)if we read for a long time our eyes become tired. When this happen it helps to stop reading and look at distance object. From the point of view of ciliary’s muscle why does this refresh the eyes?

4)which of the following are produce final image that are virtual.1)a projector 2)a camera 3)a magnifying glass 4)eyeglasses 5)a compound microscope 6)an astronomical telescope.

Answer 1

1. at the focal point of the lens or mirror. Because a parallel beam gets focused at the focal point.
2.The guy with farsight. His lenses are covex and produce a real focal spot where the sun rays conerge. for the near sighted person, the lesnses are cylindrical and will lead to beam divergence.
3. By shifting our focus from near to far off objets, the distance between the lens and the retina changes and this helps in relaxing the muscles. The distance reduces when we see distant objects and thus reduces the muscle tension.

4. Magnifying glass produces the virtual image since the object is between the lens and its focal spot.

Answer 2

Ok
1) For a convex lense, the rays coming from the focal point will move parallel to each other after emerging from the lens. So the bulb has to be placed at the focal point. If it is within the focal point the light coming out will still be diverging and not form a parallel beam. If it is beyond focal point, it will converge on emerging from the lens and form a cone.
2) The short-sighted person wears a concave lens while the farsighted person wears a convex lens. You can only create fire with the help of a convex lens at its focus, and on the opposite side of the sun. For a concave lense the rays will converge at the focus but towards the same side as the sun. Hence fire cannot be created. Only the specs of a far-sighted person can create fire.
3) The ciliary muscles will contract to reduce the diameter of the lens of the eye, so that we can read a book or see something very near to our eyes. If this is exercised for long, the muscles gets tired. When we focus our eyes to a far object, the muscles get a chance to expand and enlarge the diameter. So the eyese get relaxed.
4) A virtual image is one which cannot be cast on a screen. In your cases, only the projector and the camera produces real images which can be cast on a screen. Magnifying glass can produce real image, but when it is used for maginfication, it creates virtual image on one's eyes. Similarly, eye-glasses, compound microscope and astronomical telescope produce virtual image.

Answer 3

Dude, do your own homework. Seriously.
Just because you say "ur reasoning" doesn't mean I can't tell it's not straight off a homework sheet.