11. Long Answer Questions.
1. Write the factors on which the shape and size of a shadow depend. Describe
with an experiment that how to observe the shape and size of shadows.
2. (a) Discuss how to make a pinhole camera and the nature of image formation
by it.
(b) How can you see solar eclipse by pinhole camera?
3. (a) What do you mean by reflection and its kinds?
(b) Describe with an experiment to show the reflection of light.
Answers
Explanation:
1.The size of a shadow depends on the distance between the light source and the object that blocks that light source AND the size of the object.
If you have two people standing side-by-side outside on a sunny day, the distance to the sun is the same for both people. If one is taller than the other, that person’s shadow will be bigger.
2.a)The pinhole camera is the simplest kind of camera. It does not have a lens. It just makes use of a tiny opening (a pinhole-sized opening) to focus all light rays within the smallest possible area to obtain an image, as clearly as possible. The simple image formed using a pinhole camera is always inverted.
3.a)When a ray of light approaches a smooth polished surface and the light ray bounces back, it is called the reflection of light. The incident light ray which lands upon the surface is said to be reflected off the surface. The ray that bounces back is called the reflected ray. If a perpendicular were to be drawn on reflecting surface, it would be called normal. The figure below shows the reflection of an incident beam on a plane mirror.
b) Place a plane mirror on the table. Take a paper sheet and make a small hole in its center.
Make sure that the light in the room is not bright. Hold the sheet normal to the table.
Take another sheet and place it on the table in contact with the vertical mirror. Draw a normal line on the second sheet from the mirror. Now, light a torch on the mirror through the small hole such that the ray of light falls on the normal at the bottom of the mirror.
When the ray from this hole is incident on the mirror, it gets reflected in a certain direction. You can easily observe the incident ray, reflected ray and the normal to the mirror at the point of incidence on the sheet placed on the table.
This shows that the incident ray, the reflected ray, and the normal to the surface at the point of incidence all lie in the same plane.