Question 2 :
In the white light of sun, maximum scattering by the air molecules present in the earth's atmosphere is for:<br>
Question 3 :
What is the time difference between actual sunset and apparent sunset?
Question 4 :
Intensity of light ray in a directionafter scattering by small particles (smaller than wavelength):
Question 5 :
The split of white light into its constituent colours, by a triangular prism, is known as:
Question 6 :
Name the prism required for obtaining the spectrum of ultraviolet light:<br/>
Question 9 :
When white light enters a prism, its gets splits into its constituent colours. This is because of:<br/>
Question 11 :
The danger signals installed at the top of tall buildings are red in colour. These can be easily seen from a distance because among all other colours, the red light:<br/>
Question 14 :
At which place in eye,image is formed of a person is far-sightedness (hypermetropia) ?
Question 20 :
A person while reading a newspaper keeps it at a distance of $40$ cm, then he suffers from which of the following defects?
Question 21 :
By which optical phenomena the splitting of white light into seven constituent colours occur?<br>
Question 24 :
Intensity of light ray in a directionafter scattering by small particles (smaller than wavelength):
Question 25 :
The color of scattered light depends on ____ of the scattering particles.
Question 26 :
Which of the following phenomena contributes significantly to the reddish appearance of the sun at sunrise or sunset?<br/>
Question 27 :
When white light is passed through two consecutive prisms, the resultant will be:
Question 31 :
When Astronauts fly at higher altitude, the sky appears dark because ;
Question 34 :
For the myopic eye, the far point is farther away than the normal.
Question 35 :
On passing white light through a glass prism. Whichcolour ray will deviate maximum towards its base?
Question 37 :
What is the time difference between actual sunset and apparent sunset?
Question 38 :
The bluish colour of water in deep sea is due to:<br/>
Question 39 :
The angle between the two refracting surface of a prism is called angle of :<br/>
Question 40 :
A man can see vertical lines but he is unable to see the horizontal lines placed at the same distance. What type of lens he should use?
Question 41 :
What are the colours of the Sun observed most during sunrise/sunset and noon? <br/>
Question 44 :
Why astronauts see dark sky in space unlike blue sky on earth:
Question 46 :
Why do high rise buildings have a red light on the top of the building?
Question 47 :
Fine beam of light entering through a small hole in a dark room illuminates the particles in its path. Identify the effect associated with this process.<br/>
Question 50 :
As the thickness of the atmosphere increases colour of scattered light is found in ________order.
Question 52 :
Assertion: The setting sun appears to be red. <br>Reason: Scattering of light is directly proportional to the wavelength.
Question 53 :
Assertion: Incoming light reflected by earth is partially polarized.
Reason: Atmospheric particle polarize the light.
Question 54 :
Assertion: The setting sun appears to be red. <br>Reason: Scattering of light is directly proportional to the wavelength.
Question 55 :
What characteristic property of light is responsible for the blue colour of the sky?<br>
Question 56 :
Assertion: Fine particles in atmosphere scatter the light of shorter wavelength more.
Reason: Sky appears blue.
Question 57 :
Assertion: Fine particles in atmosphere scatter the light of shorter wavelength more.
Reason: Sky appears blue.
Question 59 :
Assertion: By roughening the surface of a glass sheet its transparency can be reduced. <br>Reason: Glass sheet with rough surface absorbs more light.
Question 62 :
Larger particles scatter light at the ____ end of the spectrum the least. <br/>
Question 64 :
During scattering of light, the amount of scattering is inversely proportional to ________ of wavelength of light.
Question 65 :
At sunrise or sunset, the sun appears to be reddish white. This is because :
Question 67 :
At sun rise or at sun set the sun appears to be reddish while at mid day it looks white. This is because
Question 69 :
When is the direction of scattered light independent of the wavelength?
Question 71 :
During scattering of light, the amount of scattering is inversely proportional to ________ of wavelength of light.
Question 72 :
Assertion: Incoming light reflected by earth is partially polarized.
Reason: Atmospheric particle polarize the light.
Question 74 :
In a beaker containing colloidal solution of sodium thiosulphate and a drop of con. sulphuric acid, light observed from side of beaker is:
Question 76 :
Larger particles scatter light at the ____ end of the spectrum the least. <br/>
Question 77 :
Assertion: By roughening the surface of a glass sheet its transparency can be reduced. <br>Reason: Glass sheet with rough surface absorbs more light.
Question 80 :
Assertion: A Diamond sparkles more than a glass imitation cut to the same shape.
Reason: The refractive index of diamond is less than that of glass.
Question 81 :
Assertion: In the absence of atmosphere the sky would appear black.<br/>
Reason: Atmosphere scatters the light and hence we get blue colour.
Question 85 :
At sunrise or sunset, the sun appears to be reddish white. This is because :
Question 86 :
Which of the following phenomena cannot be explained by scattering of light ?
Question 90 :
When is the direction of scattered light independent of the wavelength?
Question 92 :
Assertion: The setting sun appears to be red.
Reason: Scattering of light is directly proportional to the wavelength.
Question 94 :
Assertion: In the absence of atmosphere the sky would appear black.<br/>
Reason: Atmosphere scatters the light and hence we get blue colour.
Question 95 :
At sun rise or at sun set the sun appears to be reddish while at mid day it looks white. This is because
Question 96 :
Which of the following phenomena cannot be explained by scattering of light ?
Question 97 :
Assertion: A Diamond sparkles more than a glass imitation cut to the same shape.
Reason: The refractive index of diamond is less than that of glass.
Question 99 :
Assertion: Bluish colour predominates in a clear sky, since blue has a shorter wavelength and is scattered strongly.
Reason: Blue has the shortest wavelength among all colours.
Question 102 :
When the light rays converge at a point in front of the retina and then divert to form a blurred image on it, the defect is known as<br>
Question 103 :
The process of re-emission of absorbed light in all directions with different intensities by the atom or molecule is called ____________.
Question 104 :
A normal eye is not able to see objects closer than $25$cm because?
Question 105 :
The process of re-emission of absorbed light in all directions with different intensities by the atom or molecule is called ____________.
Question 107 :
A person is wearing spectacles with concave lenses for correcting vision. While not using the glasses, the image of a distant object in his case will be formed<br>
Question 109 :
The angular magnification of telescope is $30$. If all the light which passes through objective lens of diameter $80 cm$ also passes through eye piece lens then find out diameter of eye piece lens.
Question 111 :
In old age farsightedness is a defect of eye in man, in which
Question 112 :
Two point white dots are 1 mm apart on a black paper. They are viewed by eye of diameter $3\ mm $.<br/>Approximately, what is the maximum distance at which these dots can be resolved by the eye?<br/>[ take wavelength of light >500nm]
Question 113 :
One of the following is not an example of incomplete sex-linkage
Question 114 :
Myopia or near sightedness is a defect of eyes in which<br>
Question 116 :
The defective condition of accommodation of the eye in which distant objects are clearly seen but near objects are indistinct is<br>
Question 118 :
The relation among $u$, $v$ and $f$ for a mirror is:
Question 120 :
If $f$ is the focal length of a lens, then the power of the lens is equal to
Question 121 :
The magnification of an image by a convex lens is positive only when the project is placed:
Question 123 :
The value of the focal length of the lens is equal to the value of the image distance when the rays are
Question 125 :
The image of an object formed by a device isalways virtual and small. The device may be
Question 126 :
Which of the following is not a use of concave lens?
Question 127 :
Which of the following term is not associated with a lens?
Question 128 :
The radius curvature for a convex lens is $40\ cm$, for each surface. Its refractive index is $1.5$. The local length will be
Question 129 :
Height of the image of an object on an principal axis produced by a convex lens is double the focal length of lens is $20 cm$, then image distance from the lens is:
Question 130 :
Which of the following is not a characteristic of image formed by Concave lens ?
Question 131 :
State whether true or falseA convex mirror is used for obtaining a real and magnified image.
Question 132 :
State whether true or false : The degree of convergence of divergence of light rays achieved by a lens is expressed in terms of its power.
Question 133 :
The focal length of a combination of lenses formed with lenses having powers of $+2.50\ D$ and $-3.75\ D$ will be
Question 136 :
Convex lens are used in eyeglasses to correct which type of defect?<br>
Question 139 :
The focal length of a convex mirror is $20\ cm$ its radius of curvature will be
Question 140 :
A convex lens is used to form real image of an object on a screen. It is observed that even when the positions of the object and that screen are fixed are two position of the lens to form real images. If the heights of the images are $4\ cm$ and $9\ cm$ respectively the height of the object is
Question 142 :
A symmetric double convex lens is cut in two equal parts by a plane perpendicular to the principal axis. If the power of the original lens is $4 D$, the power of cut lens will be ________.
Question 143 :
The ratio of the sine of angle  of incidence to the sine of angle of refraction is a constant for :
Question 144 :
What is the nature of image formed by Concave lens ?
Question 146 :
The power of a lens is $+2.0D$. Find its focal length and state the kind of the lens.<br>
Question 147 :
The radii of curvature of both the sides of a convex lens are $15cm$ and if the refractive index of material of the lens is $1.5$. Then focal length of lens in air is _______cm.
Question 148 :
A rod is placed in a beaker of full of water. It appears to be bent inside the water. Which of the following property of light is responsible for the rod appearing to be bent?
Question 149 :
The power of a lens having a focal length of $1 cm$ is :<br/>
Question 150 :
State whether true or false:A concave lens forms a magnified or diminished image depending on the distance of object from it.<br/>
Question 152 :
An object 20 cm from lens, has a virtual image at 10 cm from the object. The power of the lens is
Question 154 :
State whether true or false.<br/>A convex mirror always forms a real image.
Question 155 :
A short sighted person can see distinctly only those objects which lie between $10cm$ and $100cm$ from him, The power of the spectacle lens required to see a distance object is
Question 158 :
No matter how far you stand from a mirror, your image appears erect. The mirror is likely to be<br>
Question 159 :
State whether true or false:The angle of incidence is always smaller than angle of refraction when a ray travels from air to glass, at an oblique angle
Question 160 :
$ \dfrac{\sin i}{\sin r}  =$constant, the value of constant depends upon<br/>a) Pair of media <br/>b) Color of incident light<br/>c) Wave length <br/>d) Refracting nature of material<br/>
Question 162 :
Which of the following mirrors forms an image which is virtual and smaller in size?
Question 163 :
State the direction of incident ray which after reflection from a spherical mirror retraces its path:
Question 164 :
To observe the hydra bud clearly. Raju should see it first under the low power lens and then under the high power lens in order to see 
Question 165 :
What is the angle of incidence when a ray of light incident on a concave mirror from its centre of curvature?
Question 167 :
On the basis of their experiment, "To trace the path of a ray of light through a rectangular glass slab," students of a class arrived at which one of the following conclusions :
Question 168 : <p>An object placed $10 cm$ in front of a lens has an image $20<br>cm$ behind the lens. What is the power of the lens (In dioptre)?</p>
Question 169 :
A glass slab is placed in the path of a beam of convergent light; the point of convergence of light
Question 170 :
If the angle of incidence increases gradually then angle of refraction also_______. <br/>
Question 171 : <p>One face of a rectangular glass plate$6{\text{ }}cm$ thick is silvered. An object held$8{\text{ }}cm$ in front of the fist face, forms an image$12{\text{ }}cm$ behind the silvered face. The refractive index of the glass is:</p>
Question 172 :
An air bubble in a glass with refractive index $1.5$ (near normalincidence) i.e. $5\ cm$ deep when viewed from one surface and $3\ cm$ deep when viewed from the opposite face. The thickness(in $cm$) of the is.
Question 173 :
A diverging meniscus lens has a focal length of -20 cm. If the lens is held 10 cm from the object, the magnification is :
Question 174 :
The difference in the number of wavelengths, when yellow light propagates through air and vacuum columns of the same thickness is one. The thickness of the air column is :(Refractive index of air $\mu _{a}=$1.0003 ; Wavelength of yellow light in vacuum $= 6000A^{\circ}$)<br/>
Question 176 :
A square card of side length 1 mm is being seen through a magnifying lens of focal length 10 cm. The card is placed at a distance of 9 cm from the lens. The apparent area of the card through the lens is
Question 177 :
An under-water swimmer cannot see very clearly even in absolutely clear water because of:
Question 178 :
Frosted glass is widely used for translucent windows. The region where a transparent adhesive tape is stuck over the frosted glass becomes transparent. The most reasonable explanation for this is :
Question 179 :
A concave mirror produces $2$ times magnified real image of an object placed at $5 cm$ in front of it. Where is image located?
Question 180 :
Why does light bends while travelling from one medium to another?<br>
Question 181 :
Light of frequency $\nu$, wave length $ \lambda $ travelling with a velocity $v$ enters into a glass slab of refractive index $ \mu $ then frequency, wave length and velocity of the wave in glass slab respectively are :<br/>
Question 182 :
A object is placed at 30 cm on the principle axis of the convex lens from the lens and an image is formed 60 cm from the lens. If focal length of the lens is 20 cm then calculate the magnification.
Question 183 :
A convex lens of focal length 80 cm and concave lens of focal length 50 cm are combined together. What will be their resultant power?<br>
Question 185 :
The magnification of the image when an object is placed at a distance x from the principle focus of a mirror of focal length f is?
Question 186 :
In aerial mapping a camera uses a lens with a $100\ cm$ focal length. The height at which the airplane must fly,so that the photograph of a $1\ km$ long strip on theground fits exactly on the $20\ cm$ long filmstrip of thecamera, is
Question 187 :
A ray of light is incident on a glass slab making an angle of $60^0$ with the surface. Calculate the angle of refraction in glass and the velocity of light in glass if the refractive index of glass and the velocity of light in air are 1.5 and 3.0 x 10$^{8}$ m/s respectively.<br/>
Question 188 :
A persons sees clearly at a distance of $ 100 cm $, then power of lens used to see object at $40 cm$ is
Question 189 :
A biconvex lens of focal length f forms a circular image of radius r of sun in focal plane. Then which option is correct?<br/>
Question 190 :
A man can see distinctly from a distance of $0.5$ metre. If he wants to read a book placed at a distance of $25 \,cm$, then what should be the power of lens ?
Question 191 :
The image formed by objective lens of compound telescope will be:
Question 192 :
We want a mirror that will make an object look larger. What combination of image and object distances (from the mirror) will accomplish this?
Question 193 :
A ray of light travelling inside a rectangular glass block of refractive index $\sqrt 2$ is incident on the glass-air interface at an angle of incidence of $45^o$. The refractive index of air is one. Under the these conditions the ray will
Question 194 :
A sound wave is travelling in a medium in which the velocity is $v$. It is incident in the second medium in which the velocity of the wave is $2v$. What should be the minimum angle of incidence in the first medium, so that the wave fails to cross the surface of separation of the two media?
Question 195 : After tracing the path of a ray of light passing through a rectangularglass slab for four different values of the angle of incidence, a studentreported his observations in tabular form as given below :<br><table class="wysiwyg-table"><tbody><tr><td><br>S.No</td><td><i</td><td><r</td><td>< e</td></tr><tr><td><br>I</td><td>${30^0}$</td><td>${19^0}$</td><td>${29^0}$<br></td></tr><tr><td>II</td><td>${40^0}$</td><td>${28^0}$</td><td>${40^0}$</td></tr><tr><td>III</td><td>${50^0}$</td><td>${36^0}$</td><td>${50^0}$</td></tr><tr><td>IV</td><td>${60^0}$</td><td>${40^0}$</td><td>${59^0}$</td></tr></tbody></table>The best observation is :
Question 196 :
A beam of light passes through a sheet of plastic and out into the air. The beam makes ${\theta}_{1}$ angles with the normal as it passes through the plastic and the angle the beam of light makes with the normal as it passes into the air is ${\theta}_{2}$. The refractive index for air is $1$ and The refractive index for plastic is $2$.<br/>Calculate the value of $\sin{{\theta}_{2}}$, in terms of ${\theta}_{1}$?
Question 197 :
Two thin lenses of focal lengths $20 cm$ and $25 cm$ areplaced in contact. The effective power of the combination is
Question 198 :
A ray of light is incident at an angle i on a glass slab of refractive index $\mu$. The angle between reflected and refracted light is $90^o$. Then the relationship between i and $\mu$ is.<br>
Question 200 :
Magnification produced by spherical lens is $+2.5$. What is the nature of image?
Question 201 :
If linear magnification for a spherical mirror is $\dfrac{3}{2}$, then we may write: (symbols have their usual meanings) 
Question 202 :
A concave mirror produces $10$ times enlarged image (real) of an object placed $1 cm$ in front of it. Where is the image located?
Question 203 :
The linear magnification for a spherical mirror is the ratio of the size of the image to the size of the object, and is denoted by m. Then m is equal to (symbols have their usual meanings)
Question 205 :
The focal length of a convex lens is $25cm$. Its power will be:
Question 208 :
Let the $\mathrm{x}-\mathrm{y}$ plane be the boundary between two transparent media. Medium 1 in $\mathrm{z}\geq 0$ has a refractive index of $\sqrt{2}$ and medium 2 with $\mathrm{z}< 0$ has a refractive index of $\sqrt{3}$. A ray of light in medium 1 given by the vector $\vec{\mathrm{A}}=6\sqrt{3}\hat{\mathrm{i}}+8\sqrt{3}\hat{\mathrm{j}} + 10\hat{\mathrm{k}}$ is incident on the plane of separation. The angle of refraction in medium 2 is<br>
Question 209 :
Identify the power of the lens in increasing order for the following cases<br/>1) lens of focal length 10 cm<br/>2) lens of focal length 10 m<br/>3) lens of focal length 2 m<br/>4) lens of focal length 50 m
Question 210 :
A thin plane membrane separates hydrogen at27$^o$C from hydrogen at 127$^o$C, both being at thesame pressure. A plane sound wave enters from the cooler to the hotter side. If the angle of incidenceon the membrane is 30$^o$C, then the angle ofrefraction is <br>
Question 211 :
Two thin lenses have combined power of $10\ D$. When separated by $20\ cm$ their equivalent power is $6.25\ D$. Their individual powers in $D$ are
Question 212 :
An object is placed upright on the axis of a thin convex lens at a distance of four focal lengths ($4f$) from the center of the lens. An inverted image appears at a distance of $\dfrac{4}{3} f$ on the other side of the lens. What is the ratio of the height of the image of the height of the object?
Question 213 :
For the same angle of incidence, the angles of refraction in media P, Q, R and S are $50^o, 40^o, 30^o, 20^o$, respectively. The speed of light is minimum in medium :<br/>
Question 214 :
The resolving power of an astronomical telescope is $0.2$ seconds. If the central half portion of the objective lens is covered, the resolving power will be:-
Question 216 :
A ray of light falls on a transparent glass slab of refractive index $1.62$. What is the angle of incidence, if the reflected ray and reflected ray are mutually perpendicular ?
Question 217 :
Two lenses whose powers are $4D$ and $-2D$ are kept in contact. The power of the compound lens is:
Question 218 :
A $2.5$ dioptre lens forms a virtual image which is $4$ times the object placed perpendicularly on the lens. Then the required distance of the object from the lens is .
Question 219 :
A short linear object of length $b$ lies along the axis of a concave mirror of focal length $f$ at a distance u from the pole of the mirror. The size of the image is approximately equal to :<br>
Question 220 :
An object is placed at $30$ cm distance from a concave mirror of focal length $20$ cm, then nature, magnification of the image will be:
Question 221 :
A symmetric double convex lens is cut in two equal parts by a plane containing the principal axis. If the power of the original lens was 4 D, the power of a divided lens will be
Question 223 :
In vacuum, to travel distance 'd', light takes time 't' and in medium to travel distance $'5d'$, it takes time 'T'. The critical angle of the medium is.<br>
Question 224 :
A short linear object of length $b$ lies along the axis of a concave mirror of focal length $f$ at a distance $u$ from the pole of the mirror. The size of the image is approximately equal to:<br/>
Question 225 :
Image of an object at infinity is formed by a convex lens of focal length $30 \ cm$ such that the size of the image is $2 \ cm$. If a concave lens of focal length $20\  cm$ is placed in between the convex lens and the image, at a distance $26\  cm$ from the convex lens, size of the new image is:
Question 226 : In the table below, column I lists various mirrors  and lenses and column II their uses, qualities or properties.<br/><table class="wysiwyg-table"><tbody><tr><td>column  I</td><td>Column II</td></tr><tr><td>I. Plane mirror</td><td>A. Feels thinner in the middle.</td></tr><tr><td>II. Concave mirror</td><td>B. Always forms virtual image.</td></tr><tr><td>III. Convex mirror</td><td>C. Always forms virtual image of smaller size.</td></tr><tr><td>IV. Concave lens </td><td>D. Is used by dentists to examine teeth.</td></tr><tr><td>V. Convex lens</td><td>E. Can be used as reading glass.<br/></td></tr></tbody></table>The correct matching is:
Question 227 :
Aconvex lens of radii of curvature 20 cm and 30 cm respectively. It is silveredat the surface which has smaller radius of curvature. Then it will behave as $(\mu_g\, = \, 1.5)$
Question 228 :
An image of a bright square is obtained on a screen with the aid of a convergent lens. The distance between the square and the lens is $40\ cm$. The area of the image is nine times larger than that of the square. Select the correct statement(s).
Question 229 :
The diameter of the reflecting surface of spherical mirror is called ..............
Question 230 :
Let the x-z plane be the boundary between two transparent media. Medium $1$ in $z\ge 0$ has a refractive index of $\sqrt { 2 } $ and medium $2$ with $z< 0$ has refractive index of $\sqrt { 3 } $. A ray of light in medium $1$ given by the vector $\vec { A } =6\sqrt { 3 } \hat { i } +8\sqrt { 3 } \hat { j } -10\hat { k } $ is incident on the plane of separation. The angle of refraction in medium $2$ is:
Question 231 :
A small object of linear dimension $x$ lies on the axis of an optical mirror of local length $f$ at a distance $a$ from mirror. The linear dimension of image:
Question 232 :
Three convex lenses are available having focal lengths of $4 cm, 40 cm$ and $4 m$ respectively. Which one could be used as magnifying glass?
Question 233 :
The final image in an astronomical telescope is _______ the original object . Fill in the gap.<br/>
Question 234 :
A concave shaving mirror has a radius of curvature of 35.0 cm. It is positioned so that the (upright) image of a mans face is 2.50 times the size of the face. How far is the mirror from the face?
Question 235 :
The image obtained while finding the focal length of convex lens is...................
Question 236 :
When a light of wavelength $4000$ $\displaystyle \overset { \circ  }{ A } $ in vacuum travels through the same thickness in diamond and water separately, the difference in the number of waves is $200$. Find the thickness, if refractive indices of diamond and water are $\displaystyle \frac { 5 }{ 2 } $ and $\displaystyle \frac { 4 }{ 3 } $ respectively.
Question 237 :
A flim projector magnifies a flim of area $100 $ square centimeter on screen. If linear magnification is $4$ then area of magnified image on screen will be-
Question 238 :
A water film is formed on a glass-block. A light ray is incident on water film from air at an angle of$\displaystyle { 60 }^{ \circ }$ with the normal. The angle of incidence on glass slab is<br>($\displaystyle { \mu }_{ g } = 1.5,{ \mu }_{ w } = \frac { 4 }{ 3 }$)
Question 239 :
A point object is placed on the principal axis of the convex lens of focal length 20cm at a distance 40 cm to the left on it. The diameter of the lens is 10cm. If the eye is placed 60cm to the right of the lens at a distance h below the principal axis, then max value of 'h' to see the image is
Question 240 :
What happens when a ray of light is made to fall on a mirror along the normal?<br/>
Question 241 :
The angle between the incident ray and the normal is called ________.<br>
Question 242 :
A spherical convex surface separates object and image space of refractive index $1$ and $4/3$ respectively. If radius of curvature of the surface s $0.1\ m$, its power is
Question 243 :
The reflecting surface is given by $y = \dfrac{10L}{\pi} \sin \dfrac{\pi x}{5L}$. The co-ordinates of the point where a horizontal ray becomes vertical after reflection is:
Question 244 :
The magnitude of focal length of a concave mirror is $f$. An object is placed at a distance $x$ from the focus and forms a real image. The magnification is:<br/>
Question 245 :
The focal length of a thin biconvex lens is 20 cm. when an object is moved from a distance of 25 cm in front of it to 50 cm, the magnification of its image changes from $m_{25}$ to $m_{50}$. The ratio of $m_{25}$ to $m_{50}$ is :
Question 246 :
A ray of light going towards the centre of curvature of a convex mirror ............
Question 247 :
The glancing angle of incidence is $10^{\circ}$. What will be the glancing angle of reflection?
Question 248 :
Two thin lenses of power $+3.5D, -2D$ are placed in contact. Find the power of lens combination.
Question 249 :
The distance between an object and its doubly magnified image by a concave mirror is: [ Assume $f$ = focal length]
Question 250 :
Air has refractive index $1.0003$. Find the thickness of air column which will contain one more wavelength of yellow light of $6000$ $A^0$ than in same thickness of vacuum.
Question 251 :
A $4.5 cm$ needle is placed $12 cm$ away from a convex mirror of focal length $15 cm$. Find the location of the image and the magnification.
