PPT - Light - Class 7 PDF Download

 Page 1


CHAPTER - 15 
 
LIGHT 
Page 2


CHAPTER - 15 
 
LIGHT 
1) Light travels along a straight line :- 
 Activity :- 
   Light a candle and fix it on a table. Take a piece of straight pipe or a 
rubber tube. Look at the candle through the pipe. You can see the 
candle flame. If the pipe is bent, you cannot see the candle flame. This 
shows that light travels along a straight line. 
Page 3


CHAPTER - 15 
 
LIGHT 
1) Light travels along a straight line :- 
 Activity :- 
   Light a candle and fix it on a table. Take a piece of straight pipe or a 
rubber tube. Look at the candle through the pipe. You can see the 
candle flame. If the pipe is bent, you cannot see the candle flame. This 
shows that light travels along a straight line. 
2) Reflection of light :- 
  When light falls on a mirror, the direction of light changes. 
This change in the direction of light by a mirror is called 
reflection of light. 
Activity :- Take a torch and cover its glass with a chart paper. Having a 
small hole. Spread a chart paper on a wooden board. Keep a plane mirror 
vertically on it. Direct a beam of light at an angle to the mirror. The 
direction of light changes. If the torch is moved slightly to either side, the 
direction of light also changes. 
Page 4


CHAPTER - 15 
 
LIGHT 
1) Light travels along a straight line :- 
 Activity :- 
   Light a candle and fix it on a table. Take a piece of straight pipe or a 
rubber tube. Look at the candle through the pipe. You can see the 
candle flame. If the pipe is bent, you cannot see the candle flame. This 
shows that light travels along a straight line. 
2) Reflection of light :- 
  When light falls on a mirror, the direction of light changes. 
This change in the direction of light by a mirror is called 
reflection of light. 
Activity :- Take a torch and cover its glass with a chart paper. Having a 
small hole. Spread a chart paper on a wooden board. Keep a plane mirror 
vertically on it. Direct a beam of light at an angle to the mirror. The 
direction of light changes. If the torch is moved slightly to either side, the 
direction of light also changes. 
3) Image formed by a plane mirror :- 
    i) The image is erect. 
  ii) The image is same size as the object. 
iii) The image is at the same distance from the mirror as the object is  
       in front of it. 
iv) The image is virtual (cannot be obtained on a screen). 
 v) In the image the right side appears left and the left side appears  
     right. 
Page 5


CHAPTER - 15 
 
LIGHT 
1) Light travels along a straight line :- 
 Activity :- 
   Light a candle and fix it on a table. Take a piece of straight pipe or a 
rubber tube. Look at the candle through the pipe. You can see the 
candle flame. If the pipe is bent, you cannot see the candle flame. This 
shows that light travels along a straight line. 
2) Reflection of light :- 
  When light falls on a mirror, the direction of light changes. 
This change in the direction of light by a mirror is called 
reflection of light. 
Activity :- Take a torch and cover its glass with a chart paper. Having a 
small hole. Spread a chart paper on a wooden board. Keep a plane mirror 
vertically on it. Direct a beam of light at an angle to the mirror. The 
direction of light changes. If the torch is moved slightly to either side, the 
direction of light also changes. 
3) Image formed by a plane mirror :- 
    i) The image is erect. 
  ii) The image is same size as the object. 
iii) The image is at the same distance from the mirror as the object is  
       in front of it. 
iv) The image is virtual (cannot be obtained on a screen). 
 v) In the image the right side appears left and the left side appears  
     right. 
4a) Spherical mirrors :- 
    Spherical mirrors are curved mirrors. 
    If the reflecting is inside, the spherical mirror is a concave 
mirror. 
   If the reflecting surface is outside, the spherical mirror is a 
convex mirror. 
  Eg :- A stainless steel spoon also act like a mirror. The 
inner side acts like a concave mirror and the outer side acts 
like a convex mirror 
Concave 
Convex