CBSE Class 7 Science Exemplar Chapter 15: Light NCERT Solutions
CBSE Class 7 Science Chapter 15, 'Light,' introduces students to the fascinating world of optics. This chapter explores the essential properties of light, including how it travels and interacts with objects. You'll learn about the formation of images using different types of mirrors – plane, concave, and convex – and understand how they create real or virtual, magnified or diminished images. The chapter also covers the behavior of light with lenses, explaining how they refract light to form images. Additionally, it sheds light on natural phenomena like rainbows, detailing the interplay of sunlight and water droplets. These concepts are explained through clear, step-by-step solutions designed to solidify your understanding of reflection and refraction, preparing you effectively for exams and building a robust foundation in optics.
Quick info
| Board | CBSE |
|---|---|
| Class | Class 7 |
| Subject | Science Exemplar |
| Session | 2026 |
| Language | English |
| Type | NCERT Solutions |
| Chapter | Chapter 15 |
Chapter summary
Chapter 15 of the CBSE Class 7 Science Exemplar focuses on 'Light.' This section provides NCERT Solutions that explain the nature of light, image formation by various optical devices like plane mirrors, concave mirrors, and convex mirrors. It also covers the formation of images by lenses and the phenomenon of rainbow formation. The solutions offer detailed answers to multiple-choice questions, helping students understand the characteristics of images formed by different mirrors and lenses.
Learning outcomes
- Understand the properties of light and image formation.
- Differentiate between plane, concave, and convex mirrors.
- Identify the types of images formed by different mirrors and lenses.
- Explain the formation of a rainbow.
- Solve problems related to image distance and object distance in plane mirrors.
Topics covered
Paper topics
- Light
- Mirrors
- Plane Mirror
- Concave Mirror
- Convex Mirror
- Image Formation
- Real Image
- Virtual Image
- Enlarged Image
- Diminished Image
- Lenses (implied)
- Rainbows
Important topics
- Image formation by different types of mirrors
- Characteristics of images (real/virtual, erect/inverted, size)
- Object distance and image distance in plane mirrors
- Conditions for seeing a rainbow
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Questions and Solutions
Multiple Choice Questions
1. Boojho and Paheli were given one mirror each by their teacher. Boojho found his image to be erect and of the same size whereas Paheli found her image erect and smaller in size. This means that the mirrors of Boojho and Paheli are, respectively
- plane mirror and concave mirror.
- concave mirror and convex mirror.
- plane mirror and convex mirror.
- convex mirror and plane mirror.
Explanation: A plane mirror always forms an image that is erect and of the same size as the object. A convex mirror, on the other hand, always forms an image that is erect but smaller in size compared to the object.
Multiple Choice Questions
2. Which of the following can be used to form a real image?
- Concave mirror only.
- Plane mirror only.
- Convex mirror only.
- Both concave and convex mirrors
Explanation: A concave mirror can form a real image when the object is placed at a distance greater than its focal length. A plane mirror always forms a virtual image. A convex mirror always forms a virtual image.
Multiple Choice Questions
3. If an object is placed at a distance of 0.5 m in front of a plane mirror, the distance between the object and the image formed by the mirror will be
- 2 m
- 1 m
- 0.25 m
Explanation: For a plane mirror, the image is formed behind the mirror at the same distance as the object is in front of it. Therefore, if the object is 0.5 m from the mirror, the image is also 0.5 m behind the mirror. The total distance between the object and the image is the sum of these two distances: distance (object to mirror) + distance (mirror to image) = .
Multiple Choice Questions
4. You are provided with a concave mirror, a convex mirror, a concave lens and a convex lens. To obtain an enlarged image of an object you can use either
(a) concave mirror or convex mirror.
(b) concave mirror or convex lens.
(c) concave mirror or concave lens.
(d) concave lens or convex lens.
Explanation: A concave mirror can form an enlarged image (both real and virtual, depending on the object's position). A convex lens can also form an enlarged image (both real and virtual, depending on the object's position). A convex mirror and a concave lens typically form diminished images.
Multiple Choice Questions
5. A rainbow can be seen in the sky
(a) when the sun is in front of you.
(b) when the sun is behind you.
(c) when the sun is overhead.
(d) only at the time of sun rise.
Explanation: A rainbow is an optical phenomenon caused by the dispersion and reflection of sunlight in water droplets. To observe a rainbow, the sun must be behind the observer, and the light from the sun must be refracted and reflected by water droplets in front of the observer.
Multiple Choice Questions
6. An erect and enlarged image can be formed by
(a) only a convex mirror.
(b) only a concave mirror.
(c) only a plane mirror.
(d) both convex and concave mirrors
Explanation: A concave mirror can form an erect and enlarged image when the object is placed between its pole and focal point. A convex mirror always forms a diminished and erect image. A plane mirror forms an erect image of the same size as the object.
Common mistakes
- Confusing the image characteristics formed by concave and convex mirrors.
- Incorrectly calculating the object-image distance for a plane mirror.
- Misunderstanding which optical devices can form enlarged images.
- Confusing the conditions for observing a rainbow.
Revision tips
- Review the characteristics of images formed by plane, concave, and convex mirrors.
- Practice the calculation for image distance in a plane mirror.
- Understand the conditions required for seeing a rainbow.
- Draw ray diagrams (if applicable in further exercises) to visualize image formation.
Practice MCQs
Q1. Boojho's mirror shows an erect and same-sized image, while Paheli's mirror shows an erect and smaller image. What are their mirrors, respectively?
Explanation: A plane mirror always forms an erect image of the same size as the object. A convex mirror forms an erect image that is always smaller than the object.
Q2. Which of the following optical devices can be used to form a real image?
Explanation: A concave mirror can form a real image when the object is placed beyond its focal point. Plane mirrors always form virtual images, and convex mirrors also form virtual images.
Q3. If an object is placed 0.5 m in front of a plane mirror, what is the total distance between the object and its image?
Explanation: In a plane mirror, the image is formed as far behind the mirror as the object is in front. So, the distance between the object and the image is twice the object distance from the mirror (0.5 m + 0.5 m = 1 m).
Q4. To obtain an enlarged image of an object, which optical devices can be used?
Explanation: A concave mirror can form an enlarged, erect, virtual image (when object is within focal length) or an enlarged, inverted, real image (when object is between F and 2F). A convex lens can form an enlarged, erect, virtual image (when object is within focal length) or an enlarged, inverted, real image (when object is between F and 2F).
Q5. Under what condition can a rainbow be seen in the sky?
Explanation: A rainbow is formed due to the dispersion of sunlight by raindrops. To see a rainbow, the observer must be positioned between the sun and the rain, with the sun at their back.
Q6. Which optical device can form an erect and enlarged image?
Explanation: A concave mirror can form an erect and enlarged image when the object is placed between the pole and the focal point. A convex mirror always forms a diminished, erect image. A plane mirror forms an erect image of the same size.
Frequently asked questions
What are the key concepts covered in Chapter 15: Light for Class 7 Science?
Chapter 15 covers the basic properties of light, how images are formed by plane, concave, and convex mirrors, and the conditions under which a rainbow appears in the sky.
How do plane mirrors form images?
A plane mirror always forms a virtual, erect image that is the same size as the object and located as far behind the mirror as the object is in front.
Can a convex mirror form a real image?
No, a convex mirror always forms a virtual, erect, and diminished image, regardless of the object's position.
What is the difference between the images formed by a concave mirror and a convex lens?
Both concave mirrors and convex lenses can form enlarged images. However, a concave mirror can form both real (inverted) and virtual (erect) images, while a convex lens can also form both real (inverted) and virtual (erect) images.
What conditions are necessary to see a rainbow?
To see a rainbow, sunlight must be present, and there must be water droplets in the air (like after rain). The observer must also have their back to the sun.
How can 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, mirrors, and image formation, which are frequently tested in exams.
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