Class 10 Science Chapter 9 Practice Question Answers - Light Reflection and Refraction

Fill in the Blanks:
Q1: When light passes from a rarer to a denser medium, it bends _______ the normal.
Ans: towards

Q2: The point at which the incident ray meets the mirror is called the _______ point.
Ans: incident

Q3: The angle between the incident ray and the normal is known as the angle of _______.
Ans: incidence

Q4: The type of mirror used in a magnifying glass is a _______ mirror.
Ans: convex

Q5: The phenomenon responsible for the dispersion of white light into its component colors is called _______.
Ans: dispersion

Short Answer Questions
Q6: Define the term 'refraction' of light.
Ans: Refraction is the bending of light when it passes from one transparent medium to another, due to a change in its speed.

Q7: State Snell's Law.
Ans: Snell's Law states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant when a ray of light passes from one medium to another. Mathematically, it can be written as: n1 sin θ1 = n2 sin θ2, where n1 and n2 are the refractive indices of the two media, and θ1 and θ2 are the angles of incidence and refraction, respectively.

Q8: Explain the term 'total internal reflection' of light.
Ans: Total internal reflection occurs when a ray of light traveling in a denser medium strikes the boundary with a rarer medium at an angle greater than the critical angle. In such cases, the light is completely reflected back into the denser medium, and no refraction occurs.

Q9: Differentiate between a real image and a virtual image.
Ans: A real image is formed when actual light rays converge at a point after reflecting or refracting, and it can be captured on a screen. A virtual image, on the other hand, is formed when the apparent path of light rays appears to diverge from a point behind the mirror or lens, and it cannot be captured on a screen.

Q10: Why does a pencil appear to be bent when placed in a glass of water?
Ans: The pencil appears bent due to the phenomenon of refraction. When light travels from water (denser medium) to air (rarer medium), it bends away from the normal, making the part of the pencil in water appear shifted or bent.

Long Answer Questions
Q11: Explain how a convex lens forms an image of an object.
Ans: A convex lens forms an image by refracting light rays that pass through it. When parallel rays of light pass through a convex lens, they converge at a point on the other side of the lens called the focus. This point is the principal focus of the lens. If an object is placed beyond twice the focal length, a real inverted image is formed. If the object is placed within the focal length, a virtual and erect image is formed.

Q12: Describe the difference between regular and diffuse reflection.
Ans: Regular reflection occurs when a smooth and polished surface reflects light rays in a specific direction, such as in a mirror. Diffuse reflection occurs when a rough and irregular surface scatters light rays in various directions, leading to the formation of non-distinct images.

Q13: Why does the sky appear blue to us?
Ans: The sky appears blue due to Rayleigh scattering. The Earth's atmosphere contains tiny particles and molecules that scatter sunlight. Blue light, being of shorter wavelength, scatters more than other colors, making the sky predominantly blue when viewed from all directions.

Q14: Explain the formation of a rainbow.
Ans: A rainbow is formed when sunlight is refracted, internally reflected, and then refracted again inside raindrops in the atmosphere. Different colors of light are refracted by different amounts, causing them to spread out and form a circular arc of colors in the sky.

Q15: How does the human eye focus on near and distant objects?
Ans: The human eye adjusts its focus using a process called accommodation. When focusing on a near object, the ciliary muscles contract, causing the lens to become more convex, which increases its refractive power. For distant objects, the ciliary muscles relax, allowing the lens to become flatter, reducing its refractive power. This adjustment ensures that clear images are formed on the retina for objects at varying distances.