NCERT Class 7 Science Chapter 11 guides us through different concepts and principles related to light. We begin our journey with the definition of light and the path of light. Thereafter, we explore different types of objects based on their interaction with light. Furthermore, we will learn about different types of images and types of spherical mirrors. In addition, we also explore types of lenses. Besides, we also get to know about rainbows. You can understand all concepts in these CBSE Class 7 Science notes. Keep reading!!
This Blog Includes:
- Introduction to NCERT Class 7 Science Chapter 11
- Reflection of Light
- Spherical Mirrors
- NCERT Solutions Class 7 Science Chapter 11: Light
Introduction to NCERT Class 7 Science Chapter 11
NCERT Class 7 Science Chapter 11 deals with light and its properties. Also, we are introduced to image formation and objects based on their interaction with light. Let us proceed!!
Light is a natural agent that facilitates sight and helps us visualise objects. It is a form of energy that travels in a straight line.
Path of the Light
Blocking the source of light, such as a candle flame, with an object demonstrates that light travels in a straight line. Also, this is evident when we attempt to observe the flame through a straight pipe and then with a bent pipe.
Classification of Objects Based on Interaction with Light
Objects are classified into three types based on their interaction with light:
- Transparent object: An object that allows light to pass through it completely is known as a transparent object. For instance, glass.
- Translucent object: An object that allows light to pass through it partially is called a translucent object. For instance, butter paper.
- Opaque object: An object that does not allow light to pass through it is termed an opaque object. For instance, wood.
Explore: Chapter 16: Light for Class 8
Reflection of Light
When light hits a shiny surface, like a mirror, it can bounce back. This bouncing of light is called “reflection.”
So, when you see your reflection in a mirror, it is because the light from you is bouncing off the mirror and coming back to your eyes. This is how mirrors work.
Laws of Reflection
NCERT Class 7 Science Chapter 11 also introduces us to the laws of reflection, which are as follows:
- The ray of light that comes to the mirror (incident ray), the ray that bounces off the mirror (reflected ray), and an imaginary line that points straight out from the mirror’s surface at the spot where the light hits (called the “normal”) all exist in the same flat surface. This is a key principle in understanding how reflection works.
- The angle of incidence is always equal to the angle of reflection.
When light rays from an object bounce off a mirror, they either appear to come together at a specific point in front of the mirror (converge) or seem to spread apart. This point where they appear to meet is where we see a representation of the object, and it’s called an “image.”
Types of Images
- Real Image: A “real image” is created when light rays come together after reflecting off a surface. These real images can be seen on a screen or surface.
- Virtual Image: A “virtual image” is when it looks like light rays are coming together after reflecting, even though they are spreading apart. These virtual images cannot be seen on a screen or surface.
A plane mirror creates an upright, virtual image that is the same size as the object. This virtual image is located at the same distance behind the mirror as the object is in front of it. This image formed by a plane mirror is an “erect image”.
Furthermore, NCERT Class 7 Science Chapter 11 introduces us to two types of spherical mirrors, which are as follows:
- Concave mirror: A concave mirror is a spherical mirror with a reflective surface that curves inward, like the inside of a sphere.
- Convex mirror: A convex mirror is a type of spherical mirror with a reflective surface that curves outward, away from the centre of the sphere.
Images Formed by Spherical Mirrors
Spherical mirrors form two types of images:
- Concave mirror: real image
- Convex mirror: virtual image
The lens is a part of reflecting objects such as glass. It is curved on both sides. Unlike mirrors, lenses have a reflecting surface on only one side.
Types of Lenses
In NCERT Class 7 Science Chapter 11, we will learn about two types of lenses- concave lenses and convex lenses.
- Concave lens: A “concave lens’ is curved inward, with wider edges and a thinner centre.
Unlike a mirror, it does not reflect light. Instead, it causes the light passing through it to bend in different directions. This property of bending light is called “refraction”, and concave lenses are often used to correct vision problems.
- Convex lens: A ‘convex lens’ is curved outward, with a thicker centre and narrower edges.
It doesn’t merge light rays; instead, it converges them. When light passes through a convex lens, it bends and comes together at a point. Owing to this, it can be used for various optical applications, including magnifying glasses and camera lenses.
A rainbow is a natural event where sunlight is both reflected and refracted by water droplets in the atmosphere. It displays seven distinct colours: red, orange, yellow, green, blue, indigo, and violet.
Also Read: Why Sky is Blue in Colour?
NCERT Solutions Class 7 Science Chapter 11: Light
In this section, we provide you with solutions to writing questions following the NCERT Class 7 Science Chapter 11.
Ques 1. Fill in the blanks:
a. An image that cannot be obtained on a screen is called_________________.
b. Image formed by a convex____________ is always virtual and smaller
c. An image formed by a_____________ mirror is always of the same size as that of the object.
d. An image which can be obtained on a screen is called a_______________ image.
e. An image formed by a concave_______________ cannot be obtained on a screen.
a. Virtual image
Ques 2. Which of the following statements are True or False:
a. We can obtain an enlarged and erect image by a convex mirror.
b. A concave lens always forms a virtual image.
c. We can obtain a real, enlarged and inverted image by a concave mirror.
d. A real image cannot be obtained on a screen.
e. A concave mirror always forms a real image.
Ques 3. Match the following items in Column I with one or more items in Column II.
|Column I||Column II|
|a. A plane mirror||(i) Used as a magnifying glass.|
|b. A convex mirror||(ii) Can form image of objects spread over a large area.|
|c. A convex lens||(iii) Used by dentists to see enlarged image of teeth.|
|d. A concave mirror||(iv) The image is always inverted and magnified.|
|e. A concave lens||(v) The image is erect and of the same size as the object.|
|(vi) The image is erect and smaller in size than the object.|
|Column I||Column II|
|a. A plane mirror||(v) The image is erect and of the same size as the object.|
|b. A convex mirror||(ii) Can form an image of objects spread over a large area.|
|c. A convex lens||(i) Used as a magnifying glass.|
|d. A concave mirror||(iii) Used by dentists to see an enlarged image of teeth.|
|e. A concave lens||(vi) The image is erect and smaller in size than the object.|
Ques 4. State the characteristics of the image formed by a plane mirror.
Ans: Here are the characteristics of an image formed by a plane mirror:
- The size of the image is equal to the size of the object.
- The image formed by a plane mirror is virtual and erect.
- The image is laterally inverted.
Ques 5. Find out the letters of the English alphabet or any other language known to you in which the image formed in a plane mirror appears exactly like the letter itself. Discuss your findings.
Ans: Here are the alphabets:
A, H, I, M, O, T, U, V, W, X, and Y
Ques 6. What is a virtual image? Give one situation where a virtual image is formed.
Ans: A “virtual image” is when it looks like light rays are coming together after reflecting, even though they are spreading apart. These virtual images cannot be seen on a screen or surface.
The image formed by a plane mirror is virtual.
Ques 7. State two differences between a convex and a concave lens.
Ans: Here are the differences between a convex and concave lens:
|Convex Lens||Concave Lens|
|A “concave lens’ is curved inward||A ‘convex lens’ is curved outward|
|It causes the light passing through it to bend in different directions. This property of bending light is called “refraction”.||It does not merge light rays; instead, it converges them. When light passes through a convex lens, it bends and comes together at a point,|
Ques 8. Give one use each of a concave and a convex mirror.
Ans: Here are the uses of both spherical mirrors:
- Concave mirror: Used in headlights of scooters and cars
- Convex mirror: Used as side view mirrors in cars and scooters
Ques 9. Which type of mirror can form a real image?
Ans: Concave mirror
Ques 10. Which type of lens forms always a virtual image?
Ans: Concave lens
Choose the correct option in Questions 11, 12, and 13
Ques 11. A virtual image larger than the object can be produced by a
(i) Concave lens
(ii) Concave mirror
(iii) Convex mirror
(iv) Plane mirror
Ans: Option (ii) Concave mirror
Ques 12. David is observing his image in a plane mirror. The distance between the mirror and his image is 4 m. If he moves 1 m towards the mirror, then the distance between David and his image will be
(i) 3 m
(ii) 5 m
(iii) 6 m
(iv) 8 m
Ans: Option (iii) 6 m
Ques 13. The rearview mirror of a car is a plane mirror. A driver is reversing his car at a speed of 2 m/s. The driver sees in his rearview mirror the image of a truck parked behind his car. The speed at which the image of the truck appears to approach the driver will be
(i) 1 m/s
(ii) 2 m/s
(iii) 4 m/s
(iv) 8 m/s
Ans: Option (iii) 4 m/s
Ans: When light hits a shiny surface, like a mirror, it can bounce back. This bouncing of light is called “reflection.”
Ans: Refraction is the bending of light as it passes from one transparent medium into another, such as when light moves from air into water or from one type of glass into another. This bending of light occurs because light travels at different speeds in different materials. When it enters a new medium at an angle, the change in speed causes the light to change direction, and this is what we know as refraction.
Ans: Light is a natural agent that facilitates sight and helps us visualise objects. It is a form of energy that travels in a straight line.
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