PHYSICS: REVISION WORKSHEET ON LIGHT SOLVED
1. ________ objects do not cast any shadow.
Answer: Transparent
objects do not cast any shadow because they allow light to pass through them
completely.
2. Moon is a ________ object.
Answer: Non-luminous
object. (It does not produce its own light; it reflects light from the Sun).
3. Classify the following as transparent,
translucent and opaque object.
Answer: Transparent Translucent Opaque
|
Air, Water | Butter paper, Smoked glass
| Brick, Metals |
4. Is air around us always transparent?
Discuss.
Answer: No, air is not
always transparent. While clean air is transparent, it can become translucent
or even opaque if it contains high concentrations of dust, smoke, or
thick fog, which scatter and block light.
5. Classify the following as luminous and
non-luminous body. Sun, moon, tube light, stars, jelly fish,
fireflies, torch, plastic.
Answer:
- Luminous:
Sun, stars, tube light, jelly fish, fireflies, torch.
- Non-luminous:
Moon, plastic.
6. List few examples for homogenous medium
and heterogenous medium.
Answer:
- Homogenous
Medium: (Uniform composition throughout)
Vacuum, distilled water, pure glass.
- Heterogenous
Medium: (Non-uniform composition) Foggy air,
muddy water, mist.
7. Draw neat diagram for convergent beam and
divergent beam of light.
Answer: * Convergent
beam: Rays of light coming from different directions meet at a single
point.
- Divergent
beam: Rays of light start from a single point source and
spread out in different directions.
8. Define the following:
- a.
Ray of light: The straight-line path along which
light energy travels.
- b.
Optical medium: Any substance (solid, liquid, or gas)
through which light can travel.
- c.
Parallel beam of light: A collection of light
rays that are parallel to each other and never meet.
- d.
Homogeneous medium: A medium that has the same
chemical composition and physical properties at all points.
- e.
Point source of light: A source of light that is very
small, effectively a single point.
9. Identify the following words:
- a.
T _ _ _ S _ _ _ _ T (Hint: Through these objects, we can see but not very
clearly.) Answer: TRANSLUCENT
- b.
_ _ M _ N _ _ S (Hint: Sun is in this category of sources of light.)
Answer: LUMINOUS
- c.
S _ R _ _ _. (Hint: We can’t obtain an image without this.)
Answer: SCREEN
10. List the conditions required for
formation of shadow. Answer:
1. A
source of light.
2. An
opaque object to obstruct the light.
3. A
screen (or surface) where the shadow can be formed.
11. Define bioluminescence.
Answer: Bioluminescence is
the production and emission of light by a living organism (e.g., fireflies,
certain deep-sea fish) as a result of a chemical reaction within its body.
12. We can see ourselves through a mirror but
not through a window. Explain.
Answer: A mirror has a
highly polished, silvered surface that causes regular reflection,
bouncing light back to our eyes to form an image. A clear window is transparent,
so most of the light passes through it rather than reflecting back to form our
image.
13. What information does a shadow provide?
Answer: A shadow tells us
about the shape of the object and the position of the light
source. However, it does not provide details about color or texture.
14. Write one important property of light.
Explain with the help of an activity.
Answer: Property:
Light travels in a straight line (Rectilinear Propagation of Light).
Activity: Take three
cardboards with a small hole in the center of each. Align them so the holes are
in a straight line. Place a candle at one end. You can see the flame through
the holes. If you displace one cardboard, you can no longer see the flame,
proving light travels in straight lines.
15. Case Study Questions:
- a.
Why did the frosted plastic sheet not form a clear shadow?
Answer: Because frosted plastic is translucent; it allows
some light to pass through, which prevents a sharp, dark shadow from
forming.
- b.
What change caused the shadow to become larger?
Answer: Moving the light source (torch) closer to the object
(or moving the object closer to the source).
- c.
If the torch was replaced with sunlight entering through a small hole,
what device would the setup resemble? Answer:
A Pinhole Camera.
16. Three torches A, B and C shown in
figure... which will not form a shadow of the ball on the screen?
Answer: Torch C.
Light travels in straight lines; since Torch C is placed above the ball and not
in front of it relative to the screen, the shadow would be cast on the floor,
not on the vertical screen.
17. How will you convert a transparent glass
sheet into a translucent sheet? Suggest any two ways.
Answer: 1. Smear a thin
layer of oil or grease on the surface. 2. Rub the surface with sandpaper
(frosting).
18. Define Shadow and explain its two
regions.
Answer: A shadow is a dark
area formed when an opaque object blocks light.
1. Umbra: The
innermost, darkest part of a shadow where no light reaches.
2. Penumbra: The
outer, partially shaded region where only some light is blocked.
19. List the characteristics of image formed
by pinhole camera.
Answer: 1. The image is inverted
(upside down). 2. The image is real (formed on a screen). 3. The image
shows the color of the object. 4. The size of the image depends on the
distance between the pinhole and the screen.
20. Explain how a shadow is formed. Why is
the shadow always dark?
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