F.4 PHYSICS

1. A real image is one that really exists in space. A translucent screen casues light to be diffusively reflected in all directions. Thus the image can be viewed at all angles.

2.(a) This is the difference between image formed by a "spherical convex lens" and a "cylindrical convex lens". Becuase of the different shapes of the lens, the images so produced are different. A spherical lens has curvature both in the vertical and horizontal planes, thus producing inverted images (i.e. the image is upside down). A cylindrical lens has curvature only on the horizontal plane but not on the vertical plane, thus producing lateral inverted images (i.e. the image is left-right interchanged).

(b) Becuase of gravity, the circular water film at the centre of the hole is thicker than that near the circumference. Thus the film of water acts like a convex lens which could magnify objects.

(c) You could not see the pencil when the test-tube is empty is because the air-glass-water acts like a reflective surface that bends away all light rays coming out from the pencil.

But when the test-tube is filled with water, it becomes a homogeneous medium inside and outside the glass tube, reflection of light doesn't occur and the light rays from the pencil could come out from the beaker and be observed by yhe eyes.