A point source emitting 628 lumen of luminous flux uniformly
Question: A point source emitting 628 lumen of luminous flux uniformly in all direction is placed at the origin. Calculate the illuminance on a small area placed at $(1.0 \mathrm{~m}, 0,0)$ in such a way that the normal to the area makes an angle of $37^{\circ}$ with the $X$-axis. Solution:...
Read More →A source emits 31.4W of radiant flux distributed
Question: A source emits $31.4 \mathrm{~W}$ of radiant flux distributed uniformly in all direction. The luminous efficiency is 60 Iumen/watt. What is the luminous intensity of the source? Solution:...
Read More →A light source emits monochromatic light of
Question: A light source emits monochromatic light of wavelength $55 \mathrm{~nm}$. The source consume $100 \mathrm{~W}$ of electric power and emits $35 \mathrm{~W}$ of radiant flux. Calculate the overall luminous efficiency. Solution:...
Read More →A source emits light of wavelength
Question: A source emits light of wavelength $555 \mathrm{~nm}$ and $600 \mathrm{~nm}$. The radiant flux of the $555 \mathrm{~nm}$ part is $49 \mathrm{~W}$ and of the $600 \mathrm{~nm}$ part is $30 \mathrm{~W}$. The relative luminosity of $600 \mathrm{~nm}$ is $0.6$. Find (a) the total radiant flux, (b) the total luminous flux, (c) the luminous efficiency. Solution:...
Read More →The luminous flux of a monochromatic source of
Question: The luminous flux of a monochromatic source of $1 \mathrm{~W}$ is 450 lumen/watt. Find the relative luminosity at the wavelength emitted. Solution:...
Read More →The relative luminosity of wavelength
Question: The relative luminosity of wavelength $600 \mathrm{~nm}$ is $0.6$. Find the radiant flux of $600 \mathrm{~nm}$ needed to produce the same brightness sensation as produce by $120 \mathrm{~W}$ of radiant at $555 \mathrm{~nm}$. Solution:...
Read More →Using the figure. Find the relative luminosity of wavelength
Question: Using the figure. Find the relative luminosity of wavelength (a) $480 \mathrm{~nm}$, (b) $520 \mathrm{~nm}$, (c) $580 \mathrm{~nm}$ (d) $600 \mathrm{~nm}$ Solution: According to figure: (a) Relatives luminosity of wavelength $480 \mathrm{~nm}$ is $0.14$ (b) Relatives luminosity of wavelength $520 \mathrm{~nm}$ is $0.68$ (c) Relatives luminosity of wavelength $580 \mathrm{~nm}$ is $0.92$ (d) Relative luminosity of wavelength $600 \mathrm{~nm}$ is $0.66$...
Read More →A photographic plate records sufficiently intense lines
Question: A photographic plate records sufficiently intense lines when it is exposed for 12 s to a source of 10 W. How long should it be exposed to a $12 \mathrm{~W}$ source radiating the light of same colour to get equally intense lines? Solution:...
Read More →A source emits 45 joules of energy in
Question: A source emits 45 joules of energy in $15 \mathrm{~s}$. What is the radiant flux of the source? Solution:...
Read More →In a Michelson experiment for measuring speed of light,
Question: In a Michelson experiment for measuring speed of light, the distance travelled by light between two reflections from the rotating mirror is $4.8 \mathrm{~km}$. The rotating mirror has a shape of a regular octagon. At what minimum angular speed of the mirror (other than zero) the image is formed at the position where a non-rotating mirror forms it? Solution:...
Read More →The image is not seen. 2. In an experiment with Foucault's apparatus,
Question: The image is not seen. 2. In an experiment with Foucault's apparatus, the various distances used are as follows: Distance between the rotating and the fixed mirror $=16 \mathrm{~m}$ Distance between the lens and the rotating mirror $=6 \mathrm{~m}$, Distance between the source and the lens $=2 \mathrm{~m}$. When the mirror is rotated at a speed of 356 revolutions per second, the image shifts by $0.7 \mathrm{~mm}$. Calculate the speed of light from these data. Solution:...
Read More →In an experiment to measure the speed of light by Fizeau's apparatus,
Question: In an experiment to measure the speed of light by Fizeau's apparatus, following data are used: Distance between the mirrors $=12.0 \mathrm{~km}$, Number of teeth in the wheel $=180$. Find the minimum angular speed of the wheel for which the image is not seen. Solution:...
Read More →The refractive index of a material M1 changes by
Question: The refractive index of a material M1 changes by $0.014$ and that of another material M2 changes by $0.024$ as the colour of the light is changed from red to violet. Two thin prisms one made of $M 1\left(A=5.3^{\circ}\right)$ and other made of $\mathrm{M} 2\left(\mathrm{~A}=3.7^{\circ}\right)$ are combined with their reflecting angles oppositely directed. (a) Find the angular dispersion produced by the combination. (b) The prisms are now combined with their refracting angles similarly ...
Read More →A thin prism of angle
Question: A thin prism of angle $6.0^{\circ}, \omega=0.07$ and $\mu_{y}=1.50$ is combined with another thin prism having $\omega=0.08$ and $\mu_{y}=1.60$ The combination produces no deviation in the mean ray. (a) Find the angle of the second prism. (b) Find the net angular dispersion produced by the combination when a beam of white light passes through it. (c) If the prisms are similarly directed, what will be the deviation in the mean ray? (d) Find the angular dispersion in the situation descri...
Read More →A thin prism of crown glass
Question: A thin prism of crown glass $\left(\mu_{r}=1.515, \mu_{v}=1.525\right.$ ) and a thin prism of flint glass ( $\mu_{r}=1.612, \mu_{v}=1.632$ ) are placed in contact with each other. Their reflecting angles are $5.0^{\circ}$ each and are similarly directed. Calculated the angular dispersion produced by the combination. Solution:...
Read More →Three thin prisms are combined as shown in figure.
Question: Three thin prisms are combined as shown in figure. The refractive indices of the crown glass for red, yellow and violet rays are $\mu_{r}, \mu_{y_{\text {and }}} \mu_{v}$ respectively and those for the flint glass are $\mu_{r}^{\prime}, \mu_{y}^{\prime}$ and $\mu_{v}^{\prime}$ respectively. Find the ration $A^{\prime} / A$ for which (a) there is no net angular dispersion and, (b) there is no net deviation in the yellow ray. Solution:...
Read More →Two prisms of identical geometrical shape are combined
Question: Two prisms of identical geometrical shape are combined with their refracting angles oppositely directed. The materials of the prisms have refractive indices $1.52$ and $1.62$ for violet light. A violet ray is deviated by $1.0^{\circ}$ when passes symmetrically through this combination. What is the angle of the prisms? Solution:...
Read More →The minimum deviations suffered by red,
Question: The minimum deviations suffered by red, yellow and violet beams passing through an equilateral transparent prism are $38.4^{\circ}, 38.7^{\circ}$ and $39.2^{\circ}$ respectively. Calculate the dispersion power of the medium. Solution:...
Read More →A thin prism is made of a material having refractive indices
Question: A thin prism is made of a material having refractive indices $1.61$ and $1.65$ for red and violet light. The dispersive power of the material is $0.07$. It is found that a beam of yellow light passing through the prism sufferes a minimum deviation of $4.0^{\circ}$ in favourable conditions. Calculate the angle of the prism. Solution:...
Read More →The refractive index of a material changes by
Question: The refractive index of a material changes by $0.014$ as the colour of the light changes from red to violet. A rectangular slab of height $2.00 \mathrm{~cm}$ made of this material is placed on a newspaper. When viewed normally in yellow light, the letters appear $1.32 \mathrm{~cm}$ below the top surface of the slab. Calculate the dispersive power of the material. Solution:...
Read More →The focal lengths of a convex lens for red,
Question: The focal lengths of a convex lens for red, yellow and violet rays are $100 \mathrm{~cm}, 98 \mathrm{~cm}$ and $96 \mathrm{~cm}$ respectively. Find the dispersive power of the material of the lens. Solution:...
Read More →A certain material has refractive indices 1.56, 1.60 and 1.68 for red,
Question: A certain material has refractive indices $1.56,1.60$ and $1.68$ for red, yellow and violet light respectively. (a) Calculate the dispersive power. (b) Find the angular dispersion produced by a thin prism of angle $6^{\circ}$ made of this material. Solution:...
Read More →A flint glass prism and a crown glass prism are to be combined
Question: A flint glass prism and a crown glass prism are to be combined in such a way that the deviation of the mean ray is zero. The refractive index of flint and crown glasses for the mean ray are $1.620$ and $1.518$ respectively. If the refracting angle of the flint prism is $6.0^{\circ}$, what would be the refracting angle of the crown? Solution:...
Read More →A lady cannot see objects closer than 40cm
Question: A lady cannot see objects closer than $40 \mathrm{~cm}$ from the left eye and/closer than $100 \mathrm{~cm}$ from the right eye. While on a mountaineering' trip, she is lost from her team. She tries to make an astronomical telescope/ from her reading glasses to look for her teammates. (a) Which glass should she use as the eyepiece ? (b) What magnification can she get with relaxed eye? Solution:...
Read More →A lady uses +1.5 D glasses to have normal vision from
Question: A lady uses $+1.5 \mathrm{D}$ glasses to have normal vision from $25 \mathrm{~cm}$ onwards. She uses a $20 \mathrm{D}$ lens as a simple microscope to see an object. Find the maximum magnifying power if she uses the microscope (a) together with her glass (b) without the glass. Do the answers suggest that an object can be more clearly seen through a microscope without using the correcting glasses? Solution:...
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