Light Worksheet-3

Light Worksheet-3

 

  1. Suppose you are in a dark room. Can you see objects in the room? Can you see objects outside the room? Explain.

 

  1. Differentiate between regular and diffused reflection. Does diffused reflection mean the failure of the law of reflection?

 

  1. Mention against each of the following whether regular or diffused reflection will take place when a beam of light strikes. Justify your answer in each case.

(a) Polished wooden table

(b) Chalk powder

(c) Card board surface

(d) Marble floor with water spread over it.

(e) Mirror

(f) Piece of paper

 

  1. State the laws of reflection.

 

  1. Describe the construction of a kaleidoscope.

 

  1. Draw a labelled sketch of the human eye.

 

  1. Explain how you can take care of your eyes.

 

  1. What is the angle of incidence of a ray if the reflected ray is at an angle of 90° to the incidence ray?

 

  1. How many images of a candle will be formed if it is placed between two parallel mirrors separated by 40 cm?

 

  1. Two mirrors meet at right angles. A ray of light is incident on one at an angle of 30° as shown in the fig. Draw the reflected ray from the second mirror.

 

Answer:

  1. We can see the objects from which reflected rays enter our eyes. When we are in a dark room then we can not see any objects. Because light doesn’t enter our eyes in dark room. We can see objects outside the room because the light is available and the rays of light enter our eyes after reflection.

 

  1. Difference between regular and diffused reflection:

1. It takes place on smooth and shiny surfaces. 1. It takes places on rough surface.

2. In this case all rays are parallel after reflection. 2. Reflected are in different direction.

Diffused reflection is not due to the failure of the laws of reflection. It is caused by the irregularities in the reflecting surface.

 

  1. (a) Regular reflection because its surface is smooth.

(b) Diffused reflection because its surface is uneven.

(c) Minute irregularities on it, so it will have a irregular reflection.

(d) A regular reflection as it will act like a plane surface.

(e) Mirror has a regular reflection. It surface is also shiny and has smooth surface.

(f) Irregular of diffused reflection because it has uneven surface.

 

  1. There are two laws of reflection.

(i) Angle of incidence is always equal to the angle of reflection.

i.e. ∠i = ∠r

(ii) The incident ray, the normal at the point of incidence and the reflected ray all lie in the same plane.

 

  1.  

Kaleidoscope is made up of three rectangular mirror strips each about 15 cm long and 4 cm wide. They are Joined together to form a prism. Then they are fixed in circular cardboard tube. The tube should be slightly longer than the mirror strips. Then one end of the tube is closed by a cardboard disc having a hole in the centre. To make the disc durable, a piece of transparent plastic sheet is pasted under the cardboard disc. At the other end, touching the mirrors, a circular plane glass plate is fixed.

 

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  1. Following cares are required for our eyes:

(i) Do not read keeping the books too closer to eyes.

(ii) Wash our eyes with cold water at least three times  a day.

(iii) Do not look at the sun or powerful light directly.

(v) Do not rub our eyes with dirty hand.

Do not put sharp things into eyes.

 

  1. The angle of incidence ray will be 45°.

 

  1. Infinite

 

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