19 questions · timed · auto-graded
Explanation: Refractive index of water is 1.33, that of kerosene is 1.44, that of mustard oil is 1.46 and that of glycerine is 1.47.
Explanation: The positive sign with the focal length indicates that it is a convex lens.
Explanation: When a point source of light is at the focus of a concave mirror or a convex lens, then emergent rays of light make a parallel beam of light. This is the reason; concave mirror is used as reflector of headlights.
Explanation: A concave mirror can form an image larger than the actual object when the object is placed between the focus and centre of curvature.
Image formation is shown below, where object (AB) is placed between the focus and centre of curvature for which image (A’B’) is obtained behind the mirror.
Explanation: The laws of reflection holds good for light reflected form any smooth surface i.e., all mirrors regardless of its shape.
Explanation: In this case, f = -15cm and hence c = -30cm; because radius of curvature is double the focal length. When and object is placed on C, its image is of the same size, inverted and is formed on C.
Explanation: $\text{m}=\frac{\text{size of image}}{\text{size of object}}$
Rear view mirror is a convex mirror, which always forms an image whose size is less than the size of the object.
Explanation: In case of all of the above, when an object is at infinity, image is highly diminished and point sized.
Explanation: In convex lens, the incident ray passing through F goes parallel to the principal axis after refraction.
Explanation: When a light ray is passed through a glass slab obliquely then, emergent ray will be parallel to the direction of the incident ray.
Explanation: $\text{n}_{\text{BA}}=\frac{\sin\text{i}}{\sin\text{r}}=\frac{\sin60^\circ}{\sin45^\circ}$
$=\frac{\frac{\sqrt{3}}{2}}{\frac{1}{\sqrt{2}}}=\frac{\sqrt{3}}{\sqrt{2}}$
Explanation: In this case, incident rays fall perpendicularly on the point of incidence. A rectangular glass slab would refract and then re-refract it.
Explanation: Since light rays in medium B goes towards normal. So it has greater restrictive index and lesser velocity of light with respect to medium A. So refractive index of medium B with respect to medium A is greater than unity.
Explanation: Any ray of light parallel to the principal axis passes through the focus (F) after reflecting from the concave mirror.
Explanation:
Explanation: A convex mirror forms virtual, erect and diminished image of the objects. So, out of given options, distant tall building can definitely be seen by using a convex mirror.
Explanation: Concave mirror forms a magnified (enlarged) image of the object if the object is placed close to the concave mirror (i.e. a distance less than its focal length). Plane mirror always forms the image of the same size as that of the object.
Explanation: $\text{m}=\frac{\text{h}'}{\text{h}}=\frac{-\text{v}}{\text{u}}\text{ or}$
$\text{u}=\frac{-\text{v}\times\text{h}}{\text{h}'}=\frac{-(-30\text{cm})\times(10\text{mm})}{-5\text{mm}}$
$=-60\text{cm}$
$\therefore\ \frac{1}{\text{f}}=\frac{1}{\text{u}}+\frac{1}{\text{v}}=-\frac{1}{60}-\frac{1}{30}=-\frac{1}{20}$
$\text{or f }=-20\text{cm}.$
