CBSE Class 7 Science Chapter 15 Light NCERT Solutions
CBSE Class 7 Science Chapter 15: Light introduces students to the fundamental concepts of light and its behavior. This chapter explores how light travels, the formation of shadows, and the reflection of light. Students will learn about the different types of mirrors, including plane, concave, and convex mirrors, and how they form images. The solutions explain the characteristics of images formed by these mirrors, such as real and virtual images, and magnification. Additionally, the chapter covers the concept of refraction of light and the working of lenses, including concave and convex lenses. Understanding these principles is crucial for grasping how optical instruments like telescopes and microscopes function. The NCERT solutions provide detailed explanations to help students understand these topics thoroughly, preparing them for examinations and building a solid foundation in optics.
Quick info
| Board | CBSE |
|---|---|
| Class | Class 7 |
| Subject | Science |
| Session | 2026 |
| Language | English |
| Type | NCERT Solutions |
| Chapter | Chapter 15 |
Chapter summary
Chapter 15, 'Light,' focuses on the basic properties of light and its behavior when reflected or refracted. The NCERT Solutions cover exercises related to identifying different types of images (real and virtual), understanding the characteristics of images formed by plane mirrors, convex mirrors, concave mirrors, and lenses. It also touches upon the concept of lateral symmetry in letters and the applications of these optical devices.
Learning outcomes
- Understand the difference between real and virtual images.
- Identify the characteristics of images formed by plane mirrors.
- Describe the properties of images formed by convex and concave mirrors.
- Explain the formation of images using convex and concave lenses.
- Recognize letters that are laterally symmetrical.
- Differentiate between the uses of various optical instruments.
Topics covered
Paper topics
- Light
- Image Formation
- Plane Mirror
- Convex Mirror
- Concave Mirror
- Convex Lens
- Concave Lens
- Real Image
- Virtual Image
- Lateral Inversion
- Image Characteristics
- Optical Instruments
Important topics
- Real vs. Virtual Images
- Image Formation by Plane Mirrors
- Image Formation by Concave Mirrors
- Image Formation by Convex Lenses
- Lateral Symmetry
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Questions and Solutions
Question 1
(a) An image that cannot be obtained on a screen is called a virtual image. Virtual images are formed where light rays appear to diverge, not converge, so they cannot be projected onto a screen.
(b) Image formed by a convex mirror is always virtual and smaller in size. Convex mirrors always form virtual, erect, and diminished images, regardless of the object's position.
(c) An image formed by a plane mirror is always of the same size as that of the object. Plane mirrors produce images that are identical in size to the object and are located as far behind the mirror as the object is in front.
(d) An image which can be obtained on a screen is called a real image. Real images are formed when light rays actually converge at a point, allowing them to be captured on a screen.
(e) An image formed by a concave lens cannot be obtained on a screen. Similar to convex mirrors, concave lenses always form virtual, erect, and diminished images that cannot be projected onto a screen.
Question 2
(a) False (F). A convex mirror always forms a virtual, erect, and diminished image. Enlarged and erect images are typically formed by concave mirrors or convex lenses under specific conditions.
(b) True (T). A concave lens always forms a virtual, erect, and diminished image, irrespective of the object's position.
(c) True (T). A concave mirror can form a real, enlarged, and inverted image when the object is placed between its pole and focal point.
(d) False (F). A real image, by definition, can be obtained on a screen because it is formed by the actual convergence of light rays.
(e) False (F). A concave mirror can form both real and virtual images depending on the position of the object. It forms a virtual image only when the object is placed between the pole and the focal point.
Question 3
The correct matches are:
- (a) A plane mirror matches with (v) The image is erect and of the same size as the object.
- (b) A convex mirror matches with (ii) Can form image of objects spread over a large area. Convex mirrors provide a wide field of view. It also matches with (vi) The image is erect and smaller in size than the object.
- (c) A convex lens matches with (i) Used as a magnifying glass. It can also form a real, inverted image (which can be magnified or diminished depending on object position), and an inverted, magnified image (iv).
- (d) A concave mirror matches with (iii) Used by dentists to see enlarged image of teeth. It can also form a real, inverted image (iv).
- (e) A concave lens matches with (vi) The image is erect and smaller in size than the object. Concave lenses always form virtual, erect, and diminished images.
Question 4
The characteristics of the image formed by a plane mirror are:
- Virtual: The image cannot be projected onto a screen.
- Erect: The image is upright, meaning it has the same orientation as the object.
- Same Size: The image is exactly the same size as the object.
- Laterally Inverted: The image is flipped horizontally; the left side of the object appears as the right side of the image, and vice versa.
- Behind the Mirror: The image is formed behind the mirror at the same distance as the object is in front of the mirror.
Question 5
The letters of the English alphabet that appear exactly like themselves when their image is formed in a plane mirror are those that possess lateral symmetry. These letters look the same when reflected horizontally.
The letters are: A, H, I, M, O, T, U, V, W, X.
These letters are symmetrical about a vertical axis passing through their center. When you hold these letters in front of a plane mirror, their reflection is identical to the original letter.
Question 6
A virtual image is an image that cannot be projected onto a screen. It is formed when the light rays originating from an object appear to diverge from a point, rather than actually converging at that point. These images are typically formed behind the mirror or on the same side as the object for lenses.
Situation where a virtual image is formed:
- When you look at your reflection in a plane mirror, you see a virtual image.
- A convex mirror always forms a virtual image.
- A concave lens always forms a virtual image.
- A concave mirror forms a virtual image when the object is placed between its pole and focal point.
Common mistakes
- Confusing real and virtual images.
- Incorrectly stating the characteristics of images formed by convex mirrors.
- Misidentifying the type of lens or mirror used in specific applications.
- Not understanding the concept of lateral inversion.
Revision tips
- Draw ray diagrams to visualize image formation by different mirrors and lenses.
- Create a table summarizing the characteristics of images formed by each optical device.
- Focus on understanding the definitions of real and virtual images.
- Practice identifying the type of mirror or lens based on the image characteristics described.
Practice MCQs
Q1. Which type of image cannot be obtained on a screen?
Explanation: A virtual image is formed where light rays do not actually converge, and thus it cannot be projected onto a screen.
Q2. A convex mirror always forms an image that is:
Explanation: Convex mirrors are known to produce images that are virtual, erect (upright), and smaller than the object.
Q3. Which optical device is used by dentists to see an enlarged image of teeth?
Explanation: A concave mirror can form a real, enlarged, and inverted image, which is useful for dentists to examine teeth closely.
Q4. Which of the following letters of the English alphabet is laterally symmetrical?
Explanation: Letters like A, H, I, M, O, T, U, V, W, X are laterally symmetrical, meaning their reflection in a plane mirror looks exactly like the original letter.
Q5. An image formed by a plane mirror is:
Explanation: A plane mirror forms an image that is virtual, erect, and has the same size as the object. It is also laterally inverted.
Frequently asked questions
What is the main topic of Chapter 15 for Class 7 Science?
Chapter 15, 'Light,' primarily deals with the properties of light and how images are formed by different types of mirrors and lenses.
What are the key differences between real and virtual images?
A real image can be formed on a screen because light rays actually converge at the image point, while a virtual image cannot be formed on a screen as the light rays only appear to diverge from the image point.
What kind of image does a plane mirror form?
A plane mirror forms an image that is virtual, erect, of the same size as the object, and laterally inverted.
Which mirror is used by dentists and why?
Dentists use a concave mirror because it can form a real, enlarged, and inverted image of teeth, allowing for a closer examination.
What does it mean for a letter to be laterally symmetrical?
A letter is laterally symmetrical if its image formed in a plane mirror is identical to the letter itself. Examples include A, H, I, M, O, T, U, V, W, X.
How do these NCERT solutions help in exam preparation?
These solutions provide clear, step-by-step explanations for each question, helping students understand the concepts of light, image formation, and the properties of optical devices, which is crucial for exam success.
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