Light – Reflection and Refraction — Science STD 10 — Question

An object 1cm tall is placed 30cm in front of a convex mirror of focal length 20cm. Find the size and position of the image formed by the convex mirror.

Show by drawing a ray-diagram that the image of an object formed by a concave lens is virtual, erect and diminished.

Draw ray diagrams showing the image formation by a concave mirror when an object is placed:

At infinity.

Describe how you could demonstrate that white light is composed of a number of colours.

A student focuses the image of a well illuminated distant object on a screen using a convex lens. After that he gradually moves the object towards the lens and each time focuses its image on the screen by adjusting the lens.

1. In which direction-towards the screen or away from the screen, does he move the lens?
2. What happens to the size of the image-does it decrease or increase?
3. What happens to the image on the screen when he moves the object very close to the lens?

Draw ray diagrams showing the image formation by a convex mirror when an object is placed:
At finite distance from the mirror.

Refractive indices of four media A, B, C and D are given below:

Medium	Refractive index
A B C D	1.33 1.44 1.52 1.65

In which of these four media is the speed of light:

1. Maximum, and
2. Minimum?

State three ways in which the strength of an electromagnet can be increased.

An electric iron of resistance 20 ohms draws a current of 5 amperes. Calculate the heat produced in 30 seconds.

Write the function of the retina in the human eye.