Science and Technology Class 9 Important Questions Chapter 11 Maharashtra Board

Reflection of Light

Short Questions

1. What is light in scientific terms?

• Light is electromagnetic radiation that causes the sensation of vision.

2. What is a mirror?

• A mirror is a polished surface that reflects light and forms clear images.

3. What are the two types of mirrors?

• Plane mirrors and spherical mirrors are the two types of mirrors.

4. What is a plane mirror made of?

• A plane mirror is made by coating a flat glass surface with a reflective film like aluminium or silver.

5. What is the nature of an image formed by a plane mirror?

• The image formed by a plane mirror is virtual, erect, and of the same size as the object.

6. What causes lateral inversion in a plane mirror?

• Lateral inversion occurs because the image is formed with left and right sides reversed.

7. What is the minimum height of a plane mirror to see a full image?

• The minimum height of a plane mirror must be half the height of the person.

8. What is a concave mirror?

• A concave mirror has a reflecting inner surface, forming part of a hollow sphere.

9. What is a convex mirror?

• A convex mirror has a reflecting outer surface, forming part of a hollow sphere.

10. What is the pole of a spherical mirror?

• The pole is the center of the mirror’s reflecting surface.

11. What is the principal focus of a concave mirror?

• The principal focus is the point where parallel rays converge after reflection.

12. What is the focal length of a spherical mirror?

• The focal length is the distance between the pole and the principal focus, f = R/2.

13. What type of image does a convex mirror always produce?

• A convex mirror always produces a virtual, erect, and diminished image.

14. What is the mirror formula?

• The mirror formula is 1/v + 1/u = 1/f, relating object distance (u), image distance (v), and focal length (f).

15. What is magnification in spherical mirrors?

• Magnification (M) is the ratio of image height (h₂) to object height (h₁), M = h₂/h₁ = -v/u.

16. Why are concave mirrors called converging mirrors?

• Concave mirrors are called converging mirrors because they focus parallel rays at a point.

17. Why are convex mirrors used in car side mirrors?

• Convex mirrors provide a wider field of view and form smaller, erect images of objects.

18. What is a real image?

• A real image is formed where light rays converge and can be projected on a screen.

19. What is the sign of the focal length for a convex mirror in Cartesian convention?

• The focal length of a convex mirror is positive in the Cartesian sign convention.

20. How many images are formed when two mirrors are at 90° to each other?

• Three images are formed, calculated using the formula n = (360°/A) – 1, where A = 90°.

Long Questions

1. What is the difference between regular and irregular reflection of light?

• Regular reflection occurs on smooth surfaces like mirrors, producing clear images. Irregular reflection happens on rough surfaces, scattering light and not forming clear images.

2. How is an image formed by a plane mirror?

• A plane mirror reflects light rays, making them appear to come from a point behind the mirror. The image is virtual, erect, and at the same distance as the object from the mirror.

3. Why do we see laterally inverted images in a plane mirror?

• Lateral inversion occurs because the left and right sides of an object are reversed in the image. This happens as each point on the object forms an image directly behind the mirror.

4. What are the uses of concave mirrors in daily life?

• Concave mirrors are used in shaving mirrors to produce magnified images and in torches to create parallel light beams. They also focus sunlight in solar devices for heating.

5. Why are convex mirrors used in vehicles and street corners?

• Convex mirrors form small, erect images, allowing a wider field of view for safety. They help drivers see around corners and prevent accidents at road intersections.

6. How does the position of an object affect the image in a concave mirror?

• In a concave mirror, objects between the pole and focus produce virtual, erect images, while those beyond the focus produce real, inverted images. The image size and position vary with object distance.

7. What is the Cartesian sign convention for spherical mirrors?

• The Cartesian sign convention takes the pole as the origin, with distances to the right and upward as positive. For concave mirrors, focal length is negative; for convex mirrors, it is positive.

8. How can you determine if a mirror is concave or convex?

• A concave mirror forms a magnified, erect image when held close, while a convex mirror forms a smaller, erect image. Observing the image’s size and orientation helps identify the mirror type.

9. What is the significance of the mirror formula in studying spherical mirrors?

• The mirror formula (1/v + 1/u = 1/f) relates object distance, image distance, and focal length. It helps calculate where and how images are formed in spherical mirrors.

10. How does magnification help understand images formed by spherical mirrors?

• Magnification (M = -v/u = h₂/h₁) shows the size ratio of the image to the object. It indicates whether the image is magnified or diminished and its orientation (erect or inverted).