Direction for Assertion \& Reason Questions

A. If both Assertion \& Reason are True and the Reason is a correct explanation of the Assertion.

B. If both Assertion and Reason are True but Reason is not a correct explanation of the Assertion

C. If Assertion is True but the Reason is False.

D. If both Assertion and Reason are False.

Q.1 Assertion : A point object moves near the principal axis of a fixed spherical mirror along a straight line. Then the image formed by the spherical mirror also moves along a straight line.

Reason : For an incident ray on a fixed spherical mirror there is a fixed reflected ray. If a point object moves along this incident ray, its image will always lie on the given reflected ray. Further an incident ray can be drawn from the moving point object in its direction of velocity towards the mirror.

(1) A

(2) B

(3) \(\mathrm{C}\)

(4) D

Q.2 Assertion : For given system \(\left(\theta=72^{\circ}\right)\), number of images formed is 4 when object is placed symmetrically.

Reason : A plane mirror always form a virtual image of a real object

(1) A

(2) B

(3) \(\mathrm{C}\)

(4) \(\mathrm{D}\)

Q.3 Assertion : We can decide the nature of a mirror by observing the size of erect image in the mirror (see figure)

Reason : The minimum distance between a real object and its real image in a concave mirror is zero.

(1) A

(2) \(\mathrm{B}\)

(3) \(\mathrm{C}\)

(4) D

Q.4 Assertion : A spherical surface of radius of curvature \(R\) separates two media of refractive index \(n_{1}\) and \(\mathrm{n}_{2}\) as shown. If an object \(\mathrm{O}\) (a thin small rod) is placed upright on principal axis at a distance \(\mathrm{R}\) from pole (i.e., placed at centre of curvature), then the size of image is not same as size of object.

Reason : If a point object is placed at centre of curvature of spherical surface separating two media of different refractive index, then the image is also formed at centre of curvature, i.e., image distance is equal to object distance.

(1) \(\mathrm{A}\)

(2) B

(3) \(\mathrm{C}\)

(4) \(\mathrm{D}\) Q.5 Assertion : If a plane glass slab is placed on the letters of different colours all the letters appear to be raised up to the same height.

Reason : Different colours have same wavelengths.

(1) A

(2) \(\mathrm{B}\)

(3) \(\mathrm{C}\)

(4) \(\mathrm{D}\)

Q.6 Assertion : Higher is the refractive index of a medium or denser the medium, lesser is the velocity of light in that medium.

Reason : Refractive index is inversely proportional to velcity.

(1) \(\mathrm{A}\)

(2) \(B\)

(3) \(\mathrm{C}\)

(4) \(\mathrm{D}\)

Q.7 Assertion : Critical angle is minimum for violet colour

Reason : Because critical angle \(\theta_{\mathrm{c}}=\sin ^{-1}\left(\frac{1}{\mu}\right)\) and \(\mu \propto \frac{1}{\lambda}\)

(1) \(\mathrm{A}\)

(2) \(\mathrm{B}\)

(3) \(\mathrm{C}\)

(4) D

Q.8 Assertion : As the temperature of a medium increases the refractive index decreases

Reason: When a ray travels from vacuum to a medium, then \(\mu\) is known as absolute refractive index of the medium

(1) \(A\)

(2) B

(3) \(\mathrm{C}\)

(4) \(\mathrm{D}\)

Q.9 Assertion : In visible light \(\mu_{\mathrm{r}}<\mu_{\mathrm{v}}\)

Reason : This follows from cauchy's formula \(\mu=\mathrm{A}+\frac{\mathrm{B}}{\lambda^{2}}+\frac{\mathrm{C}}{\lambda^{4}}\)

(1) \(\mathrm{A}\)

(2) B

(3) \(\mathrm{C}\)

(4) D

Q.10 Assertion : An air bubble in a jar of water shines brightly due to phenomenon of total internal reflection. Reason : Refraction of light is the phenomenon of change in the path of light, when it goes from one medium to another.

(1) \(\mathrm{A}\)

(2) \(\mathrm{B}\)

(3) \(\mathrm{C}\)

(4) D

Q.11 Assertion : For observing traffic at our back, we prefer to use a convex mirror.

Reason : A convex mirror has a much larger field of view than a plane mirror or concave mirror.

(1) \(\mathrm{A}\)

(2) \(\mathrm{B}\)

(3) \(\mathrm{C}\)

(4) \(\mathrm{D}\)

Q.12 Asserrtion : Just before setting, the Sun may appear to be elliptical. This happens due to refraction.

Reason : Refraction of light ray through the atmosphere may cause different magnification in mutually perpendicular directions.

(1) \(\mathrm{A}\)

(2) \(\mathrm{B}\)

(3) \(\mathrm{C}\)

(4) D

Q.13 Assertion : Critical angle of light passing from glass to air is minimum for violet colour.

Reason : The wavelength of violet light is greater than the light of other colours.

(1) \(\mathrm{A}\)

(2) \(\mathrm{B}\)

(3) \(\mathrm{C}\)

(4) \(\mathrm{D}\)

Q.14 Assertion : A concave mirror of some focal length in air is used in a medium of refractive index 2 . Then the focal length of mirror in medium remain same.

Reason : The radius of curvature of a mirror is double of the focal length.

(1) \(\mathrm{A}\)

(2) \(\mathrm{B}\)

(3) \(\mathrm{C}\)

(4) \(\mathrm{D}\) Q.15 Assertion: We cannot produce a real image by plane or convex mirrors under any circumstances.s Reason : The focal length of a convex mirror is always taken as negative.

(1) A

(2) \(\mathrm{B}\)

(3) \(\mathrm{C}\)

(4) \(\mathrm{D}\)

Q.16 Assertion : Aray incident along normal to the mirror retraces its path.

Reason : In reflection, angle of incidence is always equal to angle of reflection.

(1) \(\mathrm{A}\)

(2) \(\mathrm{B}\)

(3) \(\mathrm{C}\)

(4) \(\mathrm{D}\)

Q.17 Assertion : The frequencies of incident, reflected and refracted beam of monochromatic light incident from one medium to another are same.

Reason : The incident, reflected and refracted rays are coplanar.

(1) \(\mathrm{A}\)

(2) \(\mathrm{B}\)

(3) \(\mathrm{C}\)

(4) \(\mathrm{D}\)

Q.18 Assertion : Aconvex lens of glass \((\mu=1.5)\) behave as a diverging lens when immersed in carbon disulphide of higher refractive index \((\mu=1.65)\).

Reason : A diverging lens is thinner in the middle and thicker at the edges.

(1) A

(2) B

(3) \(\mathrm{C}\)

(4) \(\mathrm{D}\)

Q.19 Assertion : The power of a converging lens is positive and that of a diverging lens is negative

Reason : Because \(P=\frac{1}{\mathrm{f}}\)

(1) \(\mathrm{A}\)

(2) \(\mathrm{B}\)

(3) \(\mathrm{C}\)

(4) \(\mathrm{D}\)

Q.20 Assertion : There is no dispersion of light refracted through a rectangular glass slab.

Reason : Dispersion of light is the phenomenon of splitting and spreading of a beam of white light into its constituent colours.

(1) \(\mathrm{A}\)

(2) \(\mathrm{B}\)

(3) \(\mathrm{C}\)

(4) D

Q.21 Assertion : Refractive index of material of a prism depends on angle of prism A and angle of minimum deviation \(\delta_{m}\)

Reason : Because \(\mu=\frac{\sin \left(\frac{A+\delta_{\mathrm{m}}}{2}\right)}{\sin \mathrm{A} / 4}\)

(1) A

(2) B

(3) \(\mathrm{C}\)

(4) D

Q.22 Assertion : The blue colour of sky is on account of scattering of sun light.

Reason : The intensity of scattered light varies inversley as the fourth power of wavelength of light.

(1) A

(2) B

(3) \(\mathrm{C}\)

(4) D

Q.23 Assertion : The Sun looks reddish at the time of sunrise and sunset because of scattering of light. Reason : The wavelength of red colour is more than the wavelength of blue colour.

(1) A

(2) B

(3) \(\mathrm{C}\)

(4) D

Q.24 Assertion : By increasing the diameter of the objective of telescope, we can increase its range.

Reason : The range of a telescope tells us how far away a star of some standard brightness can be spotted by telescope.

(1) A

(2) \(\mathrm{B}\)

(3) \(\mathrm{C}\)

(4) \(\mathrm{D}\)

Q.25 Assertion : The resolving power of both microscope and telescope depends on the wavelength of light used.

Reason : The resolving power of a lens is the ability to resolve the two image so they are distinctly identified.

(1) \(\mathrm{A}\)

(2) \(\mathrm{B}\)

(3) \(\mathrm{C}\)

(4) \(\mathrm{D}\)