Ray Optics and Optical Test

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Ray Optics and Optical Test - 15

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Weekly Quiz Competition

Question 1
1 / -0

How much water should be filled in a container 21 cm in height, so that it appears half filled when viewed from the top of the container?
(Refractive index of water = $\displaystyle \frac { 4 }{ 3 }$ )

A
8 cm

B
10.5 cm

C
12 cm

D
14 cm

Solution

Let it be filled to height 'h'cm. Then the part not in water is (21-h)cm.
So the apparent depth of the filled portion must be (21-h)cm.
$\dfrac{real \ depth}{apparent \ depth} = refractive \ index \ of \ water$
$\dfrac{h}{21-h}=1.33$
$h=12cm$
hence, 12cm water should be filled in a container.
Question 2
1 / -0

What type of lens from the following would you have in your magnifying lens to read a page in small print ?

A
A convex lens of focal length 80 cm

B
A concave lens of focal length 80 cm

C
A concave lens of focal length 4 cm

D
A convex lens of focal length of 4 cm

Solution

A $\bf{concave\ lens}$ always produces virtual, erect and diminished images and the decrease in the size of the image depends on the position of the object.
$\therefore$ Concave lens will shrink the size of the already small letters. Hence, it is undesirable.

A $\bf{convex\ lens}$ produces real and virtual, erect and inverted, diminished, same sized and magnified image of the object, depending upon the position of the object on the principal axis.
When the object is placed at a distance less than the focal length of convex lens, an enlarged and erect image of the object is formed, which will make it easier to read small letters.

Hence, the correct answer is OPTION D.
Question 3
1 / -0

In which of the following the final image is erect ?

A
Compound microscope

B
Astronomical telescope

C
Simple microscope

D
All of the above

Solution

Answer is C.

A simple microscope is nothing but a single biconvex lens. It is referred to as magnifying glass.
The object to be viewed through a simple microscope is placed between the optic center and the focus and the image is erect, virtual and magnified.
Please refer the diagram below.
Question 4
1 / -0

The relation among $u$ , $v$ and $f$ for a mirror is:

A
$f=\dfrac{uv }{u + v}$

B
$v = \dfrac{fu}{u + f}$

C
$u=\dfrac{ fv}{f + v}$

D
all of these

Solution

As we know,

$\dfrac{1}{f}=\dfrac{1}{v}+\dfrac{1}{u}$

$\dfrac{1}{f}=\dfrac{u+v}{uv}$

${f}=\dfrac{uv}{u+v}$

hence,option A is correct.
Question 5
1 / -0

One cannot see through fog because .......... .

A
Fog absorbs light

B
Refractive index of fog is unity

C
Light suffers total internal reflection at the droplets in fog

D
Light is scattered by the droplets in fog

Solution

Answer is D.
We cannot see through fog because of scattering.
Atoms and molecules in the air, including anything carried in the air like dust or smoke, will scatter light. Water droplets, as they are present in fog, also scatter light. The light falling on an object and reflected to a viewer can be scattered to heck and back before it gets to the place where it can be 'seen' by an observer. So the observer just sees a 'whiteout' instead of being able to make out anything beyond a few meters or so.
Question 6
1 / -0

Which of the following cannot be seen by a microscope ?

A
Small nearly objects

B
Bacteria

C
Stars

D
Cells and virus

Solution

A microscope is an instrument used to see objects too small for the naked eye. microscope is used to look into smaller details like the structure of the cells and the unicellular organism. On the other hand larger objects that are very far off are the targets of a telescope. hence,stars cannot be seen by a microscope.
Question 7
1 / -0

A fisherman is standing on the bank of a lake. To a fish underwater viewing obliquely the man looks:

A
Taller than what he actually is

B
Shorter than what he actually is

C
The same height as he actually is

D
Depends on the obliquity

Solution

As shown in the diagram,
The due to the refraction of the light, the light will move away from the normal (NN') and consequently, the fish (denoted as F) will see a longer image of the fisherman (AB) as AB'.
Question 8
1 / -0

How should people wearing spectacles work with a microscope ?

A
They should keep on wearing their spectacles

B
They should never use the microscope

C
They should take off their spectacles

D
They may either put on their spectacles or they may take off their spectacles

Solution

If operators using a microscope usually wear spectacles (glasses) for activities such as working at their PC, they often need to remove them when looking through a microscope so they can align their eyes correctly with the eyepieces.
Question 9
1 / -0

How should people wearing spectacles work with a microscope?

A
They should keep on wearing their spectacles.

B
They should never use the microscope.

C
They should take off their spectacles.

D
They may either put on their spectacles or they may take off their spectacles.
Question 10
1 / -0

For reading small letters with a lens

A
one has to keep a convex lens at a distance between F and 2F from the book.

B
one has to keep a concave lens at a distance less than the focal length from the book

C
one has to keep concave lens at a distance between F and 2F from the book

D
One has to keep a convex lens at a distance less than the an focal length from the book

E
None of these

Solution

A $\bf{concave\ lens}$ always produces virtual, erect and diminished images and the decrease in the size of the image depends on the position of the object.
$\therefore$ Concave lens will shrink the size of the already small letters.

A $\bf{convex\ lens}$ produces real and virtual, erect and inverted, diminished, same sized and magnified image of the object, depending upon the position of the object on the principal axis.

When the object is placed between F and 2F of convex lens, an enlarged but inverted image of the object is formed. The magnified image makes it easier to read small letters but the inverted image is undesirable.

When the object is placed at a distance less than the focal length of convex lens, an enlarged and erect image of the object is formed, which makes it easier to read small letters.

Hence, the correct answer is OPTION D.

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Ray Optics and Optical Test - 15

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Ray Optics and Optical Test - 15

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Question 1

8 cm

10.5 cm

12 cm

14 cm

Solution

Question 2

A convex lens of focal length 80 cm

A concave lens of focal length 80 cm

A concave lens of focal length 4 cm

A convex lens of focal length of 4 cm

Solution

Question 3

Compound microscope

Astronomical telescope

Simple microscope

All of the above

Solution

Question 4

f=uvu+vf=\dfrac{uv }{u + v}f=u+vuv​

v=fuu+fv = \dfrac{fu}{u + f}v=u+ffu​

u=fvf+vu=\dfrac{ fv}{f + v}u=f+vfv​

all of these

Solution

Question 5

Fog absorbs light

Refractive index of fog is unity

Light suffers total internal reflection at the droplets in fog

Light is scattered by the droplets in fog

Solution

Question 6

Small nearly objects

Bacteria

Stars

Cells and virus

Solution

Question 7

Taller than what he actually is

Shorter than what he actually is

The same height as he actually is

Depends on the obliquity

Solution

Question 8

They should keep on wearing their spectacles

They should never use the microscope

They should take off their spectacles

They may either put on their spectacles or they may take off their spectacles

Solution

Question 9

They should keep on wearing their spectacles.

They should never use the microscope.

They should take off their spectacles.

They may either put on their spectacles or they may take off their spectacles.

Question 10

one has to keep a convex lens at a distance between F and 2F from the book.

one has to keep a concave lens at a distance less than the focal length from the book

one has to keep concave lens at a distance between F and 2F from the book

One has to keep a convex lens at a distance less than the an focal length from the book

None of these

Solution

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$f=\dfrac{uv }{u + v}$

$v = \dfrac{fu}{u + f}$

$u=\dfrac{ fv}{f + v}$