QUESTION
(1)
Fill in the blanks.
(1) The .................... is the major natural source of light for the Earth.
(2) When light falls on opaque objects, the ................. of light occurs.
(3) The functioning of a ............. camera depends on the straight-line propagation of light.
(4) A beam of light coming through a window is visible due to .............
(5) Reflection of light from still water is of the ............. type.
Solution
(1) Sun
(2) reflection
(3) pinhole
(4) dust particles
(5) regular
QUESTION
(2)
Choose the correct option.
(1) If the angle of incidence is 30°, then the angle of reflection is ............... degrees.
(2) A clear image is seen in a plane mirror because .............
(3) We can see the moon because-
(4) When are the angle of incidence and the angle of reflection equal during reflection of light?
Solution
(1) (c) 30°
(2) (a) Regular reflection of light occurs.
(3) (c) Sunlight is reflected from the surface of the moon.
(4) (a) Always
QUESTION
(3)
The moon is approximately four lakh kilometers away from the earth. The moon is visible from earth, but any sounds produced there cannot be heard on earth. Why is this so?
Solution
Light can travel through the vacuum of space, so reflected sunlight from the Moon reaches our eyes.
Sound needs a material medium such as air, water or solids to travel.
The space between the Earth and the Moon is a vacuum and has no medium for sound to travel.
Therefore, we can see the Moon but cannot hear any sounds produced there.
QUESTION
(4)
Identify whether the following statements are true or false. Rewrite the false statements after correcting them.
(1) The incident ray is called the normal.
(2) We can see an object placed in front of us through a bent pipe.
(3) Objects are clearly visible to us in a dark room.
(4) The image obtained in a pinhole camera is inverted.
Solution
1. False – The line perpendicular to the surface at the point of incidence is called the normal.
2. False – We can see an object through a straight pipe because light travels in a straight line.
3. False – Objects are not clearly visible in a dark room because there is no light.
4. True – The image obtained in a pinhole camera is inverted.
QUESTION
(5)
Who will be able to see the candle flame?
Solution
Rekha will be able to see the candle flame because her pipe is in a straight line with the candle.
Sahil, John and Ruby cannot see the flame because their pipes are bent.
Reason: Light travels in a straight line. Therefore, the candle flame can be seen only when the path from the flame to the eyes is straight.
QUESTION
(6)
Label the diagram.
Solution
QUESTION
(7)
An image of the Moon is visible on calm water. If there are ripples on the water, does the image remain the same? What is the difference and what is the reason for it?
Solution
When the water is calm, its surface is smooth like a mirror. Light reflects in an organised way, forming a clear and sharp image of the Moon.
When there are ripples, the water surface becomes rough and uneven. Light rays are reflected in different directions, so the image of the Moon becomes blurred or distorted.
QUESTION
(8)
Classify the following into two groups: Self-luminous and Non-luminous.
An aeroplane visible in the sky, a book, the sun, gold, fire, the moon, the flame of an oil lamp, the oil lamp itself, the oil in the oil lamp.
Solution
Self-luminous
The Sun
Fire
The flame of an oil lamp
Non-luminous
An aeroplane visible in the sky
A book
Gold
The Moon
The oil lamp itself
The oil in the oil lamp
PROJECTS
(1)
Astronauts who landed on the Moon via the Apollo missions placed two large mirrors there.
Find the reason for what these mirrors are used.
(2)
Construct a slightly larger pinhole camera. What trick or technique would you use to make the image appearing in it clearer?
Show this camera to your friends and display it in an exhibition.
Solution
(1)
The mirrors placed on the Moon are used to reflect laser light back to the Earth.
By measuring the time taken by the laser light to travel to the Moon and return, scientists can accurately calculate the distance between the Earth and the Moon.
(2)
To make the image clearer, I would make the pinhole very small and round.
A small pinhole allows only a narrow beam of light from each part of the object to enter the camera. This helps to form a sharper image on the screen.
I would also make the camera box completely dark from inside and close all unwanted openings so that extra light cannot enter. The screen should be smooth and white, and the inside of the box can be covered with black paper to reduce unwanted reflection of light.
These steps would help the pinhole camera produce a clearer and sharper image.
I would also make the camera box completely dark from inside and close all unwanted openings so that extra light cannot enter. The screen should be smooth and white, and the inside of the box can be covered with black paper to reduce unwanted reflection of light.
These steps would help the pinhole camera produce a clearer and sharper image.