Tag: physics

Questions Related to physics

$AB$ is a metre scale, with forces action as shown. Its mass of $100\ g$. Calculate the algebraic sum of their moments about A. answer should be in $gf$ cm

physics measurements and experimentation measuring distance of celestial bodies unconventional units of measurements units of mass

  1. 0

  2. 50

  3. 100

  4. 20

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Correct Option: B

The mass of a body is a measure of its.

physics measurements and experimentation measuring distance of celestial bodies unconventional units of measurements units of mass

  1. Momentum

  2. Force

  3. Inertia

  4. None of these

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Correct Option: C
Explanation:

The mass of a body is a measure of its inertia. By definition, inertia is the resistance to a change in the state of motion of a physical object. Mass is, therefore, a measure of inertia.

Which of the following is a non-metric unit of mass ?

physics measurements and experimentation measuring distance of celestial bodies unconventional units of measurements units of mass

  1. thou

  2. gallons

  3. pounds

  4. bar

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Correct Option: C
Explanation:

Kilogram is the basic unit of mass in the metric system

Pounds is not the metric unit of mass
So the non metric unit of mass is pounds
Therefore option $C$ is correct

In case of linearly polarised light, the magnitude of the electric field vector.

polarisation of light polarisation wave optics optics physics

  1. Does not change with time

  2. Varies periodically with time

  3. Increases and decreases linearly with time

  4. Is parallel to the direction of propagation

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Correct Option: B
Explanation:

In any type of light whether polarised or unpolarised, the magnitude of electric field vector always varies periodically with time.
Actually the change in electric field vector gives rise to periodically changing magnetic field.

If the angle between the pass axis of the polarizer and the analyzer is 45, the ratio of the intensities of original light and the transmitted light after passing through the analyzer is 

polarisation of light polarisation wave optics optics physics

  1. $\dfrac{I}{2}$

  2. $\dfrac{I}{3}$

  3. I

  4. $\dfrac{I}{4}$

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Correct Option: D
Explanation:

The intensity of the light after passing through the polariser
$I \, = \, I _0 \, cos^2\phi \, = \, I _0 \, cos^245$
$= \, I _0 \left ( \dfrac{I}{\sqrt2} \right )^2 \, = \, \dfrac{I}{2} \, \times \, \, \dfrac{I}{2} \, = \, \, \dfrac{I}{4} \,\, \left ( \because \, I _0 \, = \, \, \dfrac{I}{2} \right )$

The angle between the pass axis of polarizer and analyzer is $45^{\circ}$. The percentage of polarised light passing through analyzer is:

polarisation of light polarisation wave optics optics physics

  1. 75%

  2. 25%

  3. 50%

  4. 100%

Show answer
Correct Option: C
Explanation:

Given,

$\theta=45^0$

By malus law,
$I\propto cos^2\theta$
$I\propto (cos45^0)^2$

$I\propto \left(\dfrac{1}{\sqrt{2}}\right)^2$

$I\propto (0.5)$
The percentage of polarized light passing through analyzer is $50$%.
The correct option is C. 

When ordinary light is made incident on a quarter wave plate, the emergent light is:

polarisation of light polarisation wave optics optics physics

  1. linearly polarised

  2. circularly polarised

  3. unpolarised

  4. elliptically polarised

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Correct Option: D
Explanation:

A quarter-wave plate is basically used for the elliptical polarization of the unpolarized light incident over it. The quarter-wave plate produces the electric field at the various angle about the axis of the light and thereby making the light elliptically polarized.


In case the electric field are at an angle of $90^\circ$ from one another, it is a special case of the circularly polarized light.

Unpolarized light is incident on a plane glass surface. The angle of incidence so that reflected and refracted rays are perpendicular to each other, then:

polarisation of light polarisation wave optics optics physics

  1. $tan \, i _\beta \, = \, \dfrac{\mu}{2}$

  2. $tan \, i _\beta \, = \, \mu$

  3. $sin \, i _\beta \, = \, \mu$

  4. $cos \, i _\beta \, = \, \mu$

Show answer
Correct Option: B
Explanation:

Brewster's law,

    tan i= $\mu$
i is angle of incidence at which we get perfectly polarised reflected light.

The velocity of light in air is $3 \, \times \, 10^8 \, m \, s^{-1}$ and that in water is $2.2 \, \times \, 10^8 \, m \, s^{-1}$. The polarising angle of incidence is:

polarisation of light polarisation wave optics optics physics

  1. $45^{\circ}$

  2. $50^{\circ}$

  3. $53.74^{\circ}$

  4. $63^{\circ}$

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Correct Option: C
Explanation:

The refractive index of water, $\mu= \dfrac{\text{Speed of light in air }}{\text{Speed of light in air}}= \dfrac{3\times10^8}{2.2\times 10^8}=1.36$


From Brewster's Law:-
$tan\ i _p= \mu=1.36$
$\therefore i _p= tan^{-1}(1.36)= 53.74^o$

So correct option is $C$

At what angle of incidence will the light reflected from glass $( \mu \, = \, 1.5)$ be completely polarised

polarisation of light polarisation wave optics optics physics

  1. $72.8^{\circ}$

  2. $51.6^{\circ}$

  3. $40.3^{\circ}$

  4. $56.3^{\circ}$

Show answer
Correct Option: D
Explanation:
Brewster's angle(Angle between Reflected and Refrected ray from the glass is $90^o$ ) is given as
$tan \theta = \dfrac{n _2}{n _1}$
$n _2$=1.5
$n _1=1$ for air 
$\theta=56.30$