Light – Reflection and Refraction
Subject: General Science
Sample Practice Questions
Question 1: Why are convex mirrors preferred as rear-view mirrors in vehicles?
- They give a magnified image
- They give a wider field of view
- They give a real image
- They are cheaper to make
Explanation: Convex mirrors are preferred as rear-view mirrors because they give an erect, though diminished, image and have a wider field of view as they are curved outwards. This enables the driver to see a much larger area.
Question 2: What is Snell's law of refraction?
- sin i × sin r = constant
- sin i / sin r = constant
- i + r = constant
- i = r
Explanation: Snell's law states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for a given pair of media: sin i / sin r = constant (refractive index).
Question 3: What is the formula for magnification produced by a spherical mirror?
- m = v/u
- m = -v/u
- m = u/v
- m = -u/v
Explanation: The magnification produced by a spherical mirror is given by m = -v/u, where v is the image distance and u is the object distance. A negative value indicates a real image.
Question 4: What does a positive magnification indicate for a spherical mirror?
- Image is real and inverted
- Image is virtual and erect
- Image is enlarged
- Image is diminished
Explanation: A positive sign in the value of magnification indicates that the image is virtual and erect. A negative sign indicates that the image is real and inverted.
Question 5: What is the nature of the image formed by a plane mirror?
- Real and inverted
- Virtual and erect
- Real and erect
- Virtual and inverted
Explanation: The image formed by a plane mirror is always virtual and erect. The size of the image is equal to that of the object, and it is as far behind the mirror as the object is in front.
Question 6: What type of image is always formed by a convex mirror?
- Real and inverted
- Virtual and erect
- Real and erect
- Virtual and inverted
Explanation: A convex mirror always forms a virtual, erect, and diminished image regardless of the position of the object. This is why they are used as rear-view mirrors in vehicles.
Question 7: What is the focal length of a concave mirror if its radius of curvature is 20 cm?
- 10 cm
- 20 cm
- 40 cm
- 5 cm
Explanation: Using the relationship R = 2f, focal length f = R/2 = 20/2 = 10 cm. The focal length is half the radius of curvature.
Question 8: Where should an object be placed in front of a concave mirror to get a real, inverted, and enlarged image?
- Beyond C
- Between F and C
- At F
- Between P and F
Explanation: When the object is placed between the principal focus (F) and the centre of curvature (C) of a concave mirror, the image formed is real, inverted, and enlarged (magnified).
Question 9: What happens when a ray of light passes through the optical centre of a lens?
- It bends towards the normal
- It bends away from the normal
- It passes without any deviation
- It reflects back
Explanation: A ray of light passing through the optical centre of a lens emerges without any deviation. This is one of the rules used for drawing ray diagrams for lenses.
Question 10: Which of the following has the highest refractive index?
- Water
- Kerosene
- Diamond
- Crown glass
Explanation: According to Table 9.3, diamond has the highest refractive index (2.42) among the given options. This is why diamonds sparkle and have a high optical density.