Assignment

Chapter-Light -refraction

1. What happens to the speed of light when it enters:
a. Glass from diamond
b. Air to water

2. Calculate speed of light in a given medium if the refractive index of the medium is 1.

3. Find refractive index of water.

4. Draw a labelled diagram to show:
a. Refraction through a glass slab
b. Dispersion
c. Formation of image of same size by a convex lens
d. Human eye
e. Formation of an image which cannot be obtained on screen and is small

5. Explain construction and working of a compound microscope.

6. Explain and draw diagram of an optical instrument which is used to see heavenly objects.

7. Explain construction and working of a :
a. Photographic Camera
b. Simple Microscope

8. Write function of each of the following part:
a. Pupil
b. Ciliary Muscles
c. Cornea
d. Optic Nerve

9. Differentiate between:
a. Compound Microscope and Astronomical Telescope
b. Myopia and Hypermetropia
c. Convex Lens and Concave Lens

10. Define:
a. Optical centre
b. Focal Length
c. Focus
d. Optical Density
e. Radius of Curvature

Conductors and Insulators

Substances which do not allow electricity to pass through them easily are called insulators. These are made from materials which have a high resistance. Some substances which are insulators are air, plastic, cotton, rubber, wood, paper, glass, pure water, etc.
Substances which allow electricity to pass through them easily are called conductors. These are made from materials which have low resistances. Some examples are metals like copper, aluminium, silver, iron, brass and also salt solutions.

Diagram of Dry cell

Diagram of Human Eye

Compound Microscope

A compound microscope is an optical instrument which is used to magnify very small objects like blood cells, bacteria which otherwise cannot be seen with the naked eye.
A Laboratory Model of Compound Microscope
The essential parts of a compound microscope are two convex lenses of short focal length. These lenses are referred to as:
the objective lens or objective
the eye piece or lens
Construction of a Compound MicroscopeA compound microscope consists of the following parts:
Objective lensThe objective lens of a compound microscope is a convex lens of very short focal length (fo) that is fo <> fo.
Microscope tubeThe objective lens and the eyepiece are mounted coaxially (having a common axis) at the ends of two brass tubes which can be made to slide into each other so that the distance between the two lenses can be adjusted.
WorkingThe ray diagram given below gives the principle of a compound microscope. The object is mounted on the stand below the microscope tube. The objective lens forms a real, inverted and magnified image (I1) of the object. The image I1 acts as an object for the eye piece. The position of the eyepiece is so adjusted that the image lies within the focus of the eyepiece (Fe). The eyepiece acts like a magnifying glass and forms a virtual erect and magnified image of the object.
Image Formation in a Compound Microscope
The object (O) is placed just outside Fo, the principal focus of the objective lens.
Fe is the principal focus of the eye lens.
A real, inverted magnified image I1 is formed. The magnified image I1 acts as an object for the eye lens.
The final image I2 is virtual and is magnified still further. It is inverted compared with the object. I2 may appear 1000 times larger than the object.