Std
VII
Light
Q I
Choose the correct answer
1.
2.
3.
4.
Q II
In a pin hole camera the image formed is small and inverted.
The centres of two imaginary spheres of which the lens is a part is called centre of curvature.
The distance between the optic centre and the principal focus is called focal length.
The nature of the image formed after refraction in a convex lens when the object is placed at C1
is real , inverted , same size
Fill in the blanks
1. Objects that do not emit light of their own is called non-luminous bodies.
2. We can see partially through translucent objects.
3. Regular reflection occurs only on smooth surface.
Q III
Underline the word which does not belongs to the group
1. Stone , cardboard box , glass , aluminium sheet
2. Sun , moon , stars , bulb
Q IV Give two examples for each of the following
1. Non-luminous body Ex wall , table
2. Transparent objects Ex glass, clear water
3. Source of light Ex stars , candle
Q V Give reason
1. Light has to fall on objects for it to visible
Ans. The objects reflect the light falling on them. When this reflected light reaches the eyes
,the objects are seen. So Light has to fall on objects for it to visible
2.
The moon is called a non-luminous body.
Ans.
The moon is called a non-luminous body. Because moon reflects the sun light.
3. When a light falls on a tree a shadow is formed.
Ans. As light travels in a straight line, opaque object obstructs the path of light from falling on a
surface and shadow is formed.
4. Infinite number of images are formed when an object is placed between two parallel mirrors
facing each other.
Ans.
Infinite number of images are formed when an object is placed between two parallel
mirrors facing each other. This is because the image formed in one mirror acts as an image for
the other plane mirror.
5. A concave lens is called a diverging lens.
Ans. A concave lens diverge the light rays , So concave lens is called diverging lens.
6. In terrestrial telescope, the object is placed at the centre of curvature of the lens.
Ans.
To get real and same size of the object, In terrestrial telescope, the object is placed at
the centre of curvature of the lens.
Q VI
Answer the following
1. How are we able to see things around us ?
Ans.
We are able to see things around us because light falls on them and reaches our eyes.
Signals are then passed to brain. The brain helps us to understand the appearance , location and the
movement of the objects viewed.
2. What is the difference between luminous and non-luminous bodies? Give one example each.
Ans.
Luminous
Non-lumonous
Bodies that emit light of their own
are called luminous bodies
Ex Sun, stars
Bodies that do not emit light of their own
are called non-luminous bodies
Ex planets , stones
3. Explain the rectilinear propagation of light with the help of an experiment.
Ans.
Aim . light travels along a straight line
Materials :
Cardboards and candle
Procedure: Cut three cardboards A, B and C. Pierce a hole in them so that the holes are in the
same straight line. Place a lighted candle so that its flame is at the same height as the holes in the
card board. When the card board is shifted slightly, the flame cannot be seen through C. This is
because light cannot bend and pass through B. This shows the light travels along the straight line.
This phenomenon is called rectilinear propagation of light. For figure refer page no 77 fig 5.5
4. How translucent bodies are different from opaque bodies?
Ans. The light passes partially through translucent substance where as opaque substances do not
allow the light to pass through them at all.
5. What is reflection of light?
Ans. The bouncing back of light from any surface is called reflection.
6. Differentiate between the reflection and refraction of light.
Ans. Reflection : The bouncing back of light from any surface is called reflection.
Refraction : When light travels obliquely from one medium to another, it deviates from its original
path. This property of light is called refraction.
7. Make a list of the different types
a) convex lens
b) concave lens
Ans.
Types of Convex lens
1) Double convex lens 2) Plano-convex lens
3) concavo-convex lens
Concave lens 1) Double concave lens 2) Plano-concave lens
3) Convexo-concave lens
8.
Ans.
What is a spherical lens ?
Spherical lens is a piece of transparent material having one or two smooth ,curved surfaces.
9.
Draw the ray diagram for the following
When an object is placed beyond C1 of a convex lens Write down the nature and size of
the image
Ans. Refer page no 91 fig 5.34
Nature of the image --- Real. Inverted and diminished
10.
What is the nature and size of the image formed by convex lens when object is placed between
C1 and F1
Ans.
Nature and size of the image formed by convex lens when object is placed between
C1 and F1 real , inverted and enlarged
11.
Where should the object be placed if the nature of the image formed in a convex lens is virtual,
erect and enlarged.
Ans.
When the object is between optic centre(O) and principle focus (F) the image formed in a
convex lens is virtual, erect and enlarged.
12.
What is dispersion of light?
Ans.
The splitting of white light into several colours is called dispersion.