Class 8 Science Chapter 16 - Reflection Of Light Excercise


Important points to remember :
  1. The sense of vision is the most important among our five senses. Because  of this we can see the hills,  rivers, trees, people  and objects  around us. 
  2. Only with this we can see the  beautiful  views of nature like  clouds, rainbow, flying  birds, Moon, stars etc. 
  3. When light  rays fall on an object  their  direction  changes and they turn back. This is called the reflection of light. 
  4. There are three laws of reflection.  These are as given below. 
  5. The angle of reflection  is equal to the angle   of incidence.
  6. The  incident  ray, the  reflected  ray and the  normal lie in the same plane. 
  7. The  incident  ray  and  the  reflected  ray  are on the opposite sides of the normal. 
  8. Laws of reflection are followed in both regular  and irregular reflection. 
  9. The reflection  of light in irregular reflection  has not been obtained because the laws of reflection  are  not  followed  but  they  are  obtained  because  the  surface  is  rough.  (irregular). 
  10. In  irregular  reflection  the  angles  of  incidence  at  different  points  are  different.  But  at any one point, the angles of incidence and reflection are equal. 


Question 1: Fill in the blanks
i. The perpendicular to the mirror at the point of incidence is called....................... .

ii. The reflection of light from a wooden surface is.................. reflection.

iii. The working of Kaleidoscope is based on the properties of................... .

Answer :

i. The perpendicular to the mirror at the point of incidence is callled normal.

ii. The reflection of light from a wooden surface is diffused reflection.

iii. The working of Kaleidoscope is based on the properties of reflection of light.


Question 2: Draw a figure describing the following.
The reflecting surface of two mirrors make an angle of 90∘ with each other. If a ray incident of one mirror has an angle of incidents of 30∘, draw the ray reflected from the second mirror. What will be its angle of reflection?

Answer :

Let r2 be the angle of reflection from the second mirror.
From laws of reflection,
∠i1=∠r1=30o
Now, in ΔABC,
θ=180o−90o−60o=30o
⇒i2=60o
Hence, r2=60o

The angle of reflection of incident ray is 60∘.


Question 3: How will you explain the statement 'we cannot see the objects in a dark room?
Answer : Light enables us to see objects around us. We see an object when light falls on it and gets reflected from its surface and enters our eyes. In a dark room, there is no source of light. Thus, no light falls on the surface of objects and hence we do not see them. This is why we cannot see the objects in a dark room.


Question 4: Explain the differences between regular and irregular reflection light.
Answer :

  1. Regular type of reflection occurs on smooth surfaces such as a plane mirror. Irregular type of reflection occurs on rough surfaces such as a black board.
  2. Regular type of reflection, the reflected rays are parallel to each other. Irregular type of reflection, the reflected rays are non-parallel to each other.
  3. Regular type of reflection, the reflected rays are in one direction. Irregular type of reflection, the reflected rays are in different direction.



Question 5: Draw a figure showing the following
a. Incident Ray
b. Angle of incidence
c. Angle of reflection
d. Point of incidence
e. Reflected ray
Answer : 




Question 6: Study the following incident.
Swara and Yash were looking in a water filled vessel. They could see their images clearly in the still water. At that instant, Yash threw a stone in the water. Now their images were blurred. Swara could not understand the reason for the blurring of the images.

Explain the reason for blurring of the images to swara by answering the following questions.

i. Is there a relation between the reflection of light and the blurring of the images.?
Answer : Yes, there is a relation between the reflection of light and blurring of the images.

ii. Which types of reflection of light can you notice from this?
Answer : Initially, the water was still and its surface was smooth. Thus, regular type of reflection was taking place from its surface i.e. Because of this, we saw a clear image.
But when Yash threw a stone in the water, the water surface became rough due to which irregular type of reflection of light occurred on its surface i.e Thus, only some part of the reflected rays reached our eyes. Because of this, we see a blurred image.

iii. Are laws of reflection followed in these types of reflection? 
Answer : Yes, laws of reflection are followed in both the types of reflection.


Question 7: Solve the following examples.
a. If the angle between the plane mirror and the incident ray is 40∘, what are the angles of incidence and reflection?
Answer :
∠i + 40o=90o
⇒∠i=50o
Using law of reflection,
we have ∠i=∠r=50o

b. If the angle between the mirror and reflected ray is 23∘, what is the angle of incidence of the incidence ray? 
Answer :
∠r+ 23o=90o
⇒∠r=67o
Using law of reflection,
we have ∠i=∠r=67o


# Can you Tell
1. How do you see if the barber in a saloon has cut the  hair on your neck properly or not? 
Answer : Multiple reflection refer to reflecting a ray of light more than one.in barber's shop,we can see the back of the head using multiple reflection of two mirror.this is because the image formed by one minor.

2. What type of image do we see in a mirror? What happens to the left and right sides? 
Answer : The mirror does not reverse images from left to right, it reverses them from front to back relative to the front of the mirror. Stand facing a mirror. Point to one side. You and your mirror image are pointing in the same direction.

3. How do we see the image of the Moon in water?
Answer : According to the laws of reflection we are able to see the image of moon in water. When incident light from the moon strikes on the surface of water then some parts of the ray is gets into water and most of the part of the incident ray is reflected back , thus we are able to see the image of the moon in water.

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