Assertion-Reason Questions: Light
Question 1
Assertion (A): The speed of light decreases when it travels from air to water.
Reason (R): The refractive index of water is less than that of air.
Explanation: The assertion is true because the speed of light decreases as it enters a denser medium. However, the reason is false because the refractive index of water is higher than that of air.
Question 2
Assertion (A): The image formed by a plane mirror is virtual.
Reason (R): The image formed by a plane mirror cannot be captured on a screen.
Explanation: The assertion and reason are true, and the reason correctly explains why the image formed by a plane mirror is virtual.
Assertion (A): The speed of light in glass is less than its speed in air.
Reason (R): The refractive index of glass is greater than that of air.
Assertion (A): A concave mirror can form both real and virtual images.
Reason (R): The nature of the image depends on the object’s distance from the mirror.
Explanation: Both the assertion and reason are true, and the reason correctly explains the formation of different types of images by a concave mirror.
Assertion (A): The magnification produced by a convex lens is negative when the image is real.
Reason (R): A real image is inverted, and magnification is the ratio of the height of the image to the height of the object.
Assertion (A): The focal length of a concave mirror is negative.
Reason (R): The focus of a concave mirror lies on the same side as the reflecting surface.
Explanation: Both the assertion and reason are true, and the reason correctly explains the negative focal length of a concave mirror.
Assertion (A): A convex lens of higher curvature has a shorter focal length.
Reason (R): The focal length of a lens depends on its radius of curvature and refractive index.
Explanation: Both assertion and reason are true, and the reason explains the relationship between curvature and focal length.
Assertion (A): A convex mirror is used as a rear-view mirror in vehicles.
Reason (R): A convex mirror provides a wider field of view than a plane mirror.
Explanation: Both assertion and reason are true, and the reason correctly explains the use of convex mirrors as rear-view mirrors.
Assertion (A): A ray of light passing through the optical center of a lens does not bend.
Reason (R): The optical center of a lens has a uniform thickness.
Explanation: Both assertion and reason are true, but uniform thickness is not the reason for no deviation.
Assertion (A): The angle of incidence is equal to the angle of reflection.
Reason (R): Reflection of light follows the law of conservation of energy.
Assertion (A): A convex mirror can form a real image.
Reason (R): A convex mirror always diverges light rays.
Explanation: The assertion is false because convex mirrors cannot form real images, but the reason is true since they always diverge light rays.
Assertion (A): The focal length of a lens depends only on its material.
Reason (R): The focal length of a lens is also influenced by its curvature.
Explanation: The assertion is false because focal length depends on both material and curvature, but the reason is true.
Assertion (A): The refractive index of a medium is always greater than 1.
Reason (R): The refractive index is the ratio of the speed of light in the medium to the speed of light in vacuum.
Explanation: The assertion is false for some cases like vacuum (refractive index = 1), but the reason is true.
Assertion (A): A concave lens can produce a real image of a point source.
Reason (R): Concave lenses always produce virtual images by diverging light rays.
Explanation: The assertion is false as concave lenses cannot produce real images, but the reason is true as they diverge light rays.
Assertion (A): The speed of light in a medium decreases with an increase in wavelength.
Reason (R): The refractive index of a medium increases with an increase in wavelength.
Explanation: The assertion is true because light slows down in a medium, but the reason is false as refractive index decreases with an increase in wavelength.
Explanation: The assertion and reason are true, but conservation of energy does not directly explain the equality of angles in reflection.
Explanation: Both assertion and reason are true, and the reason correctly explains why the magnification is negative for a real image.
Assertion (A): A ray of light passing through the focus of a concave mirror becomes parallel to the principal axis after reflection.
Reason (R): Light rays parallel to the principal axis converge at the focus of a concave mirror.
Explanation: The assertion and reason are true, but the reason does not directly explain the reflection behavior of light passing through the focus.
Assertion (A): A plane mirror always forms a virtual and erect image.
Reason (R): The image distance is equal to the object distance in a plane mirror.
Explanation: The assertion and reason are true, but the equality of image and object distances does not explain the virtual and erect nature of the image.
Assertion (A): The refractive index of a medium is a measure of how much it slows down light.
Reason (R): The refractive index is defined as the ratio of the speed of light in vacuum to the speed of light in the medium.
Explanation: Both assertion and reason are true, and the reason explains why the refractive index quantifies the reduction in speed.
Assertion (A): The image formed by a convex lens is real when the object is placed beyond the focal point.
Reason (R): A convex lens converges light rays to form an image.
Explanation: Both assertion and reason are true, and the reason explains how the convex lens converges light to form a real image.
Explanation: Both the assertion and reason are true, and the reason explains why the speed of light in glass is less.
Assertion (A): A concave lens always forms a virtual, erect, and diminished image.
Reason (R): A concave lens diverges the light rays passing through it.
Explanation: Both the assertion and reason are true, but divergence of light does not directly explain the nature of the image formed by a concave lens.
Assertion (A): A ray of light passing through the center of curvature of a concave mirror retraces its path.
Reason (R): The ray of light passing through the center of curvature strikes the mirror perpendicularly.
Explanation: Both the assertion and reason are true, and the reason correctly explains why the ray retraces its path.
Assertion (A): The focal length of a convex mirror is always positive.
Reason (R): The reflected rays from a convex mirror appear to diverge from a virtual focus.
Explanation: Both the assertion and reason are true, but the reason does not directly explain why the focal length is positive.
Assertion (A): The power of a lens is inversely proportional to its focal length.
Reason (R): The focal length of a lens is directly proportional to the curvature of its surface.
Explanation: The assertion is true, but the reason incorrectly links focal length and curvature to power in an inversely proportional manner.
Assertion (A): Light bends towards the normal when it enters a denser medium from a rarer medium.
Reason (R): The speed of light increases in a denser medium.
Explanation: The assertion is true, but the speed of light decreases in a denser medium, making the reason false.
Assertion (A): A convex lens always forms a magnified image.
Reason (R): A convex lens converges parallel rays of light at its focus.
Explanation: The assertion is false because a convex lens can also form diminished images. The reason is true but does not support the assertion.
Assertion (A): The refractive index of water is greater than 1.
Reason (R): The speed of light in water is faster than in air.
Explanation: The assertion is true, but the reason is false because light travels slower in water than in air.
Assertion (A): A concave lens always forms a virtual, erect, and diminished image.
Reason (R): A concave lens diverges light rays.
Explanation: Both the assertion and reason are true, and the reason explains the behavior of a concave lens.
Assertion (A): A ray of light passing through the focus of a convex lens becomes parallel to the principal axis after refraction.
Reason (R): A convex lens converges all rays to its optical center.
Explanation: The assertion is true, but the reason is false as rays converge at the focus, not the optical center.
