Exam-style CBSE practice questions on Refraction of Light (Light – Reflection and Refraction). Try each one first, then reveal the correct answer and a step-by-step explanation. Free, from EduLevel — the AI teacher for CBSE.
Identify which of the given materials is unsuitable for manufacturing a lens.
Think about the fundamental property of a material that allows it to bend light. This property is crucial for making a lens.
Explanation: Lenses function by refracting light, which requires the material to be transparent. Clay is opaque and does not allow light to pass through, making it unsuitable for a lens.
To obtain a real image that is the same size as the object using a convex lens, where must the object be positioned?
Recall the properties of image formation by a convex lens. Consider what happens when an object is placed at different points relative to the lens and its focal points.
Explanation: A convex lens produces a real, inverted image of the same size as the object only when the object is placed at the center of curvature (2F), which is at twice the focal length.
For reading the small print in a dictionary, which of these lenses would be the most suitable choice?
To read small print, you need to magnify it, which suggests using a lens that forms a magnified, virtual image.
Explanation: A convex lens is used as a magnifying glass. The power of a lens is inversely proportional to its focal length, so a shorter focal length (5 cm) provides greater magnification than a longer one (50 cm).
Given that the absolute refractive indices for medium X and medium Y are 6/5 and 4/3, respectively, what is the refractive index of medium Y relative to medium X?
Recall the definition of relative refractive index and how it relates to the absolute refractive indices of two media.
Explanation: The refractive index of medium Y with respect to X is calculated as the ratio of the absolute refractive index of Y to that of X (n_Y / n_X). This gives (4/3) / (6/5) = 10/9.
The absolute refractive indices of water and glass are 4/3 and 3/2, respectively. If the speed of light in glass is 2 x 108 m/s, calculate the speed of light in water.
Recall the definition of the absolute refractive index of a medium, which relates to the speed of light in that medium and the speed of light in vacuum.
Explanation: The speed of light in a medium is c/n. From the data for glass, c = n_glass * v_glass = (3/2) * (2 x 108) = 3 x 108 m/s. Thus, the speed in water is v_water = c / n_water = (3 x 108) / (4/3) = (9/4) x 108 m/s. The option represents the fractional part of the speed.
An optical device, labeled 'X', is positioned at an angle in the path of a narrow, parallel beam of light. The light beam that emerges from the device is laterally displaced. Identify the device 'X'.
Consider how different optical devices interact with light rays. Think about what happens when light passes from one medium to another at an angle.
Explanation: Lateral displacement, where the emergent ray is parallel to the incident ray but shifted sideways, is a characteristic phenomenon of light refraction through a rectangular glass slab.
To form an image with a magnification of -1 on a screen using a lens with a focal length of 20 cm, what must be the object distance?
Think about the nature of the image formed by a lens when the magnification is negative. What does a negative magnification imply about the image?
Explanation: A magnification of -1 signifies a real, inverted image of the same size as the object. For a convex lens, this condition is met when the object is placed at twice the focal length (2F). Therefore, the object distance is 2 * 20 cm = 40 cm.
To obtain a real image on a screen that is the same size as the object using a convex lens, where should the object be positioned?
Think about the properties of image formation by a convex lens. What happens to the image characteristics (size, nature, and position) as the object moves closer to or farther from the lens?
Explanation: For a convex lens, when an object is placed at twice the focal length (2F), a real, inverted image of the same size is formed at 2F on the other side of the lens.
Which set of light phenomena is responsible for the formation of a rainbow in the sky?
Think about how sunlight interacts with water droplets to split into different colors and then returns to your eyes.
Explanation: A rainbow is formed when sunlight enters a raindrop (refraction and dispersion), reflects off the inner surface (total internal reflection), and exits the drop (refraction again).
The absolute refractive indices of glass and water are 3/2 and 4/3, respectively. If the speed of light in glass is 2 x 108 m/s, what is the speed of light in water?
Remember the definition of absolute refractive index: it's the ratio of the speed of light in vacuum to the speed of light in the medium. This relationship connects refractive index and speed of light.
Explanation: Using n = c/v, first find c from glass data: c = n_glass * v_glass = (3/2) * (2 x 108) = 3 x 108 m/s. Then find v_water: v_water = c / n_water = (3 x 108) / (4/3) = 2.25 x 108 m/s.
What change will be observed in the image produced by a convex lens if its upper half is covered with black paper?
Consider how a lens forms an image and what role different parts of the lens play in light collection.
Explanation: Covering half the lens reduces the amount of light passing through it, which decreases the brightness of the image. However, the full image is still formed because rays from all points of the object can still pass through the uncovered lower half of the lens.
For which color of light is the refractive index of glass at its minimum value?
Consider the phenomenon of dispersion, which is the splitting of white light into its constituent colors when it passes through a prism. This phenomenon is related to how different colors of light interact with the medium.
Explanation: The refractive index is inversely related to the wavelength of light. Red light has the longest wavelength, so it travels fastest in glass and bends the least, resulting in the minimum refractive index.
A student determines the focal length of an optical device 'A' by focusing the image of a very distant object onto a screen. The screen is located on the side of the device opposite to the object. What is device 'A'?
Consider the nature of the optical device that can form a real image on a screen from a distant object. This type of image can be projected.
Explanation: The device forms a real image on a screen, so it must be a converging device (concave mirror or convex lens). Since the image is formed on the opposite side of the device from the object, it must be a lens that refracts light through it, which is a convex lens.
A ray of light passes through a rectangular slab made of medium B (refractive index n₂) which is placed in a surrounding medium. The light enters from medium A (refractive index n₁) and exits into medium C (refractive index n₃). If the emergent ray is parallel to the incident ray, what is the correct relationship between n₁, n₂, and n₃?
Think about the conditions under which a ray of light emerges parallel to its incident path after passing through a series of media.
Explanation: For the emergent ray to be parallel to the incident ray after passing through a slab, the medium on both sides of the slab must be the same, hence n₁ = n₃. For refraction to occur, the slab (medium B) must be optically denser, so n₂ > n₁.
Two thin lenses are placed in contact, and their combined power is +1.0 D. If one of the lenses has a focal length of +20.0 cm, calculate the focal length of the second lens.
Recall the formula for the combined power of two lenses in contact. It relates the total power to the individual powers of the lenses.
Explanation: The power of the first lens is P₁ = 1/f₁ = 1/0.2m = +5D. The total power is P = P₁ + P₂, so +1D = +5D + P₂, which gives P₂ = -4D. The focal length of the second lens is f₂ = 1/P₂ = 1/(-4)m = -0.25m = -25.0 cm.
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