NCERT Solutions Science Chapter 15 Light for Class 7th
Here’s a summary of NCERT Solutions for Class 7 Science, Chapter 15: “Light.”
Nature of Light:
- Light is a form of energy that travels in straight lines.
- It can be reflected, refracted, and absorbed.
Reflection of Light:
- When light hits a surface, it bounces back. This is called reflection.
- The angle of incidence (angle at which light hits the surface) is equal to the angle of reflection (angle at which light leaves the surface).
Laws of Reflection:
- First law: The incident ray, reflected ray, and the normal (perpendicular to the surface) all lie in the same plane.
- Second law: The angle of incidence is equal to the angle of reflection.
Plane Mirrors:
- A flat mirror reflects light and forms images.
- Images formed in a plane mirror are virtual, upright, and of the same size as the object.
Refraction of Light:
- Refraction occurs when light passes from one medium to another (e.g., air to water) and bends.
- This bending happens due to a change in speed.
Lenses:
- Lenses are transparent objects that refract light to form images.
- There are two main types of lenses:
- Convex lenses: Thicker in the middle, they converge light rays.
- Concave lenses: Thinner in the middle, they diverge light rays.
Real and Virtual Images:
- Real images can be projected on a screen and are formed on the opposite side of the lens from the object.
- Virtual images cannot be projected on a screen and are formed on the same side as the object.
Applications of Light: Light is essential for vision and is used in various technologies, including cameras, microscopes, and telescopes.
NCERT Solutions Science Chapter 15 Light for 2024-2025
Q.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 in size.
(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.
Ans.(a) virtual image (b) mirror (c) plane (d) real (e) lens
Q.2.Mark ‘T’ if the statement is true and ‘F’ if it is false:
(a) We can obtain an enlarged and erect image by a convex mirror. (T/F)
(b) A concave lens always form a virtual image. (T/F)
(c) We can obtain a real, enlarged and inverted image by a concave mirror. (T/F)
(d) A real image cannot be obtained on a screen. (T/F)
(e) A concave mirror always form a real image. (T/F)
Ans. a) F (b) T (c) T (d) F (e) F
Q.3. Match the items given in Column I with one or more items of Column II
Ans.
Q.4.State the characteristics of the image formed by a plane mirror.
Ans.(i) Plane mirror forms an erect image.
(ii) It forms a virtual image.
(iii) Size of the image is same as that of the object.
(iv)Image is formed at the same distance behind the mirror as the object stands in front of it.
(v) Image formed is a laterally inverted image i.e., right hand side of the object seems to be the left hand side and vice-versa.
Q.5.Find out the letters of 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.Letters like A, H, I, M, O, T, U ,V, W etc. appear same when seen through a plane mirror
Q.6.What is a virtual image? Give one situation where a virtual image is formed.
Ans.The image which cannot be taken on a screen is called virtual image. When some object is placed very close to the concave mirror we don’t get any image on the white screen placed behind the mirror. Such image is called virtual image.
Q.7. State two differences between a convex and a concave lens.
Ans.
Q.8. Give one use each of a concave and a convex mirror.
Ans. Use of concave mirror:
Concave mirror is used by dentists to examine the teeth.
Use of convex mirror:
Convex mirror is used as side view mirror in vehicles
Q.9. Which type of mirror can form a real image?
Ans. Concave mirror can form a real image.
Q.10. Which type of lens forms always a virtual image?
Ans. Concave lens always forms a virtual image.
Choose the correct option in Questions 11-13:
Q.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. (ii) concave mirror
Q.12. David is observing his image in a plane mirror. Die 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. (iii) 6 m
Q.13. The rear view 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 rear mew 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. (ii) 4 m/s