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1.

Find out, from Table 10.3, the medium having highest optical density. Also find the medium with lowest optical density.

Answer» Highest optical density = Diamond
Lowest optical density = Air
Optical density of a medium is directly related with the refractive index of that medium. A medium which has the highest refractive index will have the highest optical density and vice-versa.
It can be observed from table 10.3 that diamond and air respectively have the highest and lowest refractive index. Therefore, diamond has the highest optical density and air has the lowest optical density.
Discussion
2.

Define one dioptre of power of a lens.

Answer» The SI unit of power of lens is dioptre which is denoted by the latter D. 1 dioptre is defined as the power of a lens of focal length 1 metre.
Discussion
3.

Name a mirror that can give an errect and enlarged image of an object.

Answer» Concave mirror.
Discussion
4.

Find the power of a concave lens of focal length `2 m`.

Answer» Focal length of concave lens, f = 2 m Power of lens, P=1/f = 1/(-2) = -0.5D
Discussion
5.

A concave mirror produces three times magnified real image of an object placed at 10 cm in front of it. Where is the image located ?

Answer» Magnification produced by a spherical mirror is given by the relation,
`m=("Height of the Image")/("Height of the Object")= -("Image Distance")/("Object Distance")`
`m=(h_(1))/(h_(0))= -u/v`
Let the height of the object, `h_(0)` = h
Then, height of the image, `h_(1)` = −3h (Image formed is real)
`(-3h)/(h)=(-v)/u`
v/u=3`
Object distance, u = −10 cm
v = 3 × (−10) = −30 cm
Here, the negative sign indicates that an inverted image is formed at a distance of 30 cm in front of the given concave mirror.
Discussion
6.

The radius of curvature of a spherical mirror is 20 cm. What is its focal length?

Answer» Radius of curvature, R = 20 cm
Radius of curvature of a spherical mirror = 2 × Focal length (f) R
`f=R//2=20//2=10`
Hence, the focal length of the given spherical mirror is 10 cm.
Discussion
7.

An object is placed at a distance of `10 cm` from a convex mirror of focal length `15 cm`. Find the position and nature of the image ?

Answer» Focal length of convex mirror, f = +15 cm
Object distance, u = −10 cm
According to the mirror formula,
`rArr1/v=1/f-1/u`
`rArr1/v=1/15-1/(-10)`
`rArr1/v=1/15+1/10`
`rArr=(2+3)/30`
`rArr=5/30`
`rArrv=6 cm`
`"Magnification"=(-v)/u=(-6)/-10=0.6`
The image is located at a distance 6 cm from the mirror on the other side of the mirror.
The positive and less than 1 of magnification indicates that the image formed is virtual and erect and diminidhed.
Discussion
8.

The refractive index of diamond is `2.42`. What is the meaning of this statement ?

Answer» The refractive index of diamond is 2.42. This means that the speed of light in diamond will reduce by a factor of 2.42 as compared to its speed in air.
In other words, the speed of light in diamond is 1/2.42 times the speed of light in vacuum.
Discussion
9.

Which of the following lenses would you prefer to use while reading small letters found in a dictionary ?A. A convex lens of focal length 50 cmB. A concave lens of focal length 50 cmC. A convex lens of focal length 5 cmD. A concave lens of focal length 5 cm

Answer» Correct Answer - c
Discussion