Class 10 – Science Extra Questions – Ch. 9 – Light Reflection and Refraction

Ans: C

Explanation: A convex lens is a lens that curves outward in its central area. This outward curve causes parallel light rays to converge at a focal point. A concave lens, on the other hand, curves inward in its central area and causes light rays to diverge. Plano-convex lenses have one flat surface and one outward-curving surface. Concavo-convex lenses have one inward-curving surface and one outward-curving surface. Therefore, a lens that curves outward in its central area is a convex lens.
Correct Option: C

Ans: B

Explanation: When light moves from a rarer medium (air) to a denser medium (water), it bends towards the normal. The angle of incidence is the angle between the incident ray and the normal, and the angle of refraction is the angle between the refracted ray and the normal. Since the light bends towards the normal, the angle of refraction will be smaller than the angle of incidence.
Correct Option: B

Ans: A

Explanation: A convex mirror always forms a virtual, erect, and diminished image, regardless of the object’s position. Virtual means the image cannot be projected onto a screen. Erect means the image is upright, and diminished means it is smaller than the object. This property makes convex mirrors ideal for rear-view mirrors as they provide a wider field of view.
Correct Option: A

Ans: C

Explanation: The magnification of a lens is given by the ratio of the image distance to the object distance. First, we need to ensure both distances are in the same units. The object distance is 0.09 meters, which is equal to 9 centimeters. The image distance is given as 36 centimeters. Therefore, the magnification is image distance / object distance = 36 cm / 9 cm = 4.
Correct Option: C

Ans: C

Explanation: A convex lens is a lens that converges rays of light that are travelling parallel to its principal axis. Therefore, it is also known as a converging lens. A concave lens, on the other hand, is a diverging lens.
Correct Option: C

Ans: A

Explanation: A convex lens forms an image by gathering light rays from an object and converging them. Blocking a portion of the lens simply reduces the total amount of light that can pass through and be refracted. This reduction in light intensity will make the resulting image dimmer. However, as long as there is still an unobstructed portion of the lens that can intercept light rays from all parts of the object, the image will still be complete, meaning it will show all parts of the object. Blocking a portion does not distort the image or prevent it from being formed entirely. Magnification and brightness are not directly affected in the way described in option D. Option B is incorrect because while the image might be slightly less sharp due to diffraction effects at the edges of the blocked portion, it will still be complete. Option C is incorrect because a complete blockage is needed for the image to be absent.
Correct Option: A

Ans: C

Explanation: The power of a lens in dioptres is the reciprocal of its focal length in metres. The formula is Power (P) = 1 / focal length (f). Given that the focal length is 0.5 meters, the power is P = 1 / 0.5 m = 2 dioptres.
Correct Option: C

Ans: D

Explanation: A concave lens is a diverging lens. When a real object is placed in front of a concave lens, it always forms an image that is on the same side of the lens as the object. This type of image cannot be projected onto a screen, making it a virtual image. Concave lenses also always produce an erect (upright) image. Furthermore, for any real object placed at any distance from a concave lens, the image formed is always smaller than the object, meaning it is diminished. Therefore, the image formed by a concave lens for any real object is always virtual, erect, and diminished.
Correct Option: D

Ans: A

Explanation: A convex lens converges light rays. When an object is placed beyond the focal length of a convex lens, a real, inverted image is formed. The nature of the image (diminished, same size, or magnified) depends on the object’s position relative to the focal length and twice the focal length (2f). The focal length (f) is 20cm. Twice the focal length (2f) is 40cm. When the object distance is greater than 2f (i.e., greater than 40cm), the image formed is real, inverted, and diminished.
Correct Option: A

Ans: A

Explanation: When light travels from a medium with a higher refractive index to a medium with a lower refractive index, it bends away from the normal. This is because the speed of light increases in the medium with a lower refractive index, causing the wavefront to tilt and bend away from the perpendicular line (normal) to the surface. This phenomenon is described by Snell’s Law. If the angle of incidence is large enough, total internal reflection can occur, but the question asks what happens to the light ray in general, and bending away from the normal is the characteristic behavior in this scenario.
Correct Option: A