Embibe Experts Solutions for Chapter: Light - Reflection and Refraction, Exercise 1: Exercise

Lenses are used in many optical devices. Complete the table above about the images formed by some optical devices.

You are in a dark room. You have a box containing some lenses. Only one of them is a converging lens. Describe how, by just feeling the lenses, you can pick out the converging lens.

A door is fitted with a security lens. The security lens allows a person to see a visitor before opening the door. The security lens is concave.

Below is an incomplete ray diagram representing a visitor standing near the security lens.

(a) Complete the diagram above to show how an image of the visitor is formed by the concave lens. Draw an arrow to represent the image.

(b) The visitor moves further away from the security lens in the door. How does the size of the image change?

(a) Light travelling from water into air is refracted in the same way as when light travels from plastic into air. The diagram below shows a large bottle, filled with water. The bottle is made from clear plastic.

Draw onto the diagram the path of the light ray as it passes out of the bottle into the air.

(b) In some countries, people are too poor to pay for electricity. Some people living in small houses with no natural light use bottles filled with water as a sort of light bulb. The bottles are fitted into small holes in the roof of the house. Sunlight goes into the bottle of water. When the light leaves the bottle, the light is refracted, causing sunlight to spread into the room.

(i) What is likely to be the most important outcome of using this simple device to provide light?

Tick one box in the table below.

(ii) Suggest one disadvantage of using this device compared with using a light bulb.

Here is a diagram of an optical fibre.

(i) What is the name given to the dotted line on the diagram?

(ii) Where the ray of light touches the edge of the optical fibre, it is reflected. Draw the reflected ray onto the diagram.

A diver is working under water and a ray of light from his lamp strikes the surface of the water at an angle of $55°$ to the horizontal. Take the refractive index of the water as being $1.33$.

At what angle to the horizontal will the ray travel after it leaves the water?

There are two basic types of telescopes, refractors and reflectors. The refractor telescope uses a lens to gather and focus light. The reflector telescope uses a mirror to gather and focus light. All modern research telescopes and large amateur ones are of the reflector type because of its advantages over the refractor telescope.

On 25th December 2021, NASA launched the most advanced telescope that has ever been created. A telescope that can potentially change our understanding of the universe. This structure, which somewhat looks like a giant honeycomb on a boat is the James Webb Space Telescope or JWST for short. So, what is it that makes this telescope the most advanced one yet? James Webb Space Telescope is a reflecting telescope that uses a combination of curved mirrors that reflect light and form an image.

The diagram below shows light rays in a reflecting telescope.

(i) Describe what the mirrors and the eyepiece do to the light rays to form an image of a distant star.

(ii) Explain an advantage of using a telescope instead of the naked eye to look at stars.

Shyam was visiting his grandparents. He had the opportunity to go through his grandmother's coin collection. His grandmother was using a lens to read the letters on the back of a coin. The image height of the letters on the coin is $9.0 \mathrm{mm}$. The magnification produced by the lens which was used by his grandmother is known to be $6.0$. Calculate the height of the letters on the coin.