Tag: physics

Questions Related to physics

According to Maxwell's equation, the velocity of light in any medium is expressed as

physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

  1. $\displaystyle\frac{1}{\sqrt{\mu _0\varepsilon _o}}$

  2. $\displaystyle\frac{1}{\sqrt{\mu\varepsilon}}$

  3. $\displaystyle\sqrt{\frac{\mu}{\varepsilon}}$

  4. $\displaystyle\sqrt{\frac{\mu _0}{\varepsilon}}$

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Correct Option: B
Explanation:

Velocity of light in a medium,

$\displaystyle c=\frac{1}{\sqrt{\mu _0\varepsilon _o\mu _r\varepsilon _r}}=\frac{1}{\sqrt{\mu\varepsilon}}$

Maxwell's equation describe the fundamental laws of

physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

  1. electricity

  2. magnetism

  3. mechanics

  4. both (A) and (B)

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Correct Option: D
Explanation:

Maxwell's equation describe the fundamental laws of electricity and magnetism. His equations describe how electric and magnetic fields are generated and altered by each other and by charges and currents.

According to Maxwell's hypothesis, a changing electric field gives rise to

physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

  1. an electromagnetic force

  2. electric displacement current

  3. magnetic field

  4. pressure gradient

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Correct Option: C
Explanation:
$Answer:-$ C option
$\nabla \times B={ \mu  } _{ 0 }(J+{ \epsilon  } _{ 0 }\dfrac { dE }{ dt } )$
using this equation of maxwell we can say changing electric field $\dfrac{dE}{dt}$ induces magnetic field.

The electric field associated with an e.m. wave in vacuum is given by $\vec {E} = 40\cos (kz - 6\times 10^{8}t)\hat {i}$, where $E, z$ and $t$ in $volt/m$, meter and seconds respectively. The value of wave vector $k$ is

physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

  1. $6m^{-1}$

  2. $3m^{-1}$

  3. $2m^{-1}$

  4. $0.5m^{-1}$

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Correct Option: C
Explanation:
Given: The electric field associated with  an electromagnetic wave in vacuum is given by $\vec E =40 \cos(kz−6\times 10^8t)\hat i$  , where E, z and t are in volt per meter, meter and second respectively.
To find the value of wave vector k
Solution: 
We know electromagnetic wave eqution is
$E=E _0\cos(kz-\omega t)$
And given equation is
$\vec E =40 \cos(kz−6\times 10^8t)\hat i$
By comparing these two, we get
$\omega=6\times10^8$ and 
$E _0=40\hat i$
we also know,
Speed of electromagnetic wave, $v=\dfrac \omega k$
where v is the speed of the light
Hence, $k=\dfrac \omega v\\\implies k=\dfrac {6\times 10^8}{3\times 10^8}\\\implies k=2m^{-1}$
is the required value

Wavelength of light in different media are proportional to:

physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

  1. speed of light in that medium

  2. Amplitude of light in that medium

  3. frequency of light in that mrdium

  4. Nove of above

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Correct Option: A

The Maxwell's equation : $\oint \vec { \mathrm { B } }$ . $\vec { \mathrm { d } 1 } = \mu _ { 0 } \left( \mathrm { i } + \varepsilon _ { 0 } \cdot \frac { \mathrm { d } \phi _ { \mathrm { E } } } { \mathrm { dt } } \right)$ is a statement of

physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

  1. Faraday's law of induction

  2. Modified Ampere's law

  3. Gauss's law of electricity

  4. Gauss's law of magnetism

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Correct Option: A

What is the displacement current between the square plate of side 1 cm of a capacitor, if electric field between the, plates is changing at the rate of 3 x $10^6 V _m^{-1}S^{-1}$? 

physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

  1. 2.7 x $10^{-6}$ A

  2. 3.2 x $10^{-6}$ A

  3. 4.2 x $10^{-6}$ A

  4. 4.0 x $10^{-6}$ A

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Correct Option: B

In Maxwell's velocity distribution curve area under the graph 

physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

  1. Increases when temperature is increased

  2. Deccreases when temperature is increased

  3. Remains same at all temperature

  4. Depends on the pressure of the gas

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Correct Option: C
Explanation:

Area under the Maxwell's velocity distribution curve gives the number of particles. Since number of particles remains the same at all the temperatures, so the area under the curve also remains the same at all temperature.

If a plane electromagnetic wave satisfies the equation $\dfrac{\partial ^2E _x}{\partial _z^2}= C^2 \dfrac{\partial^2E _x}{\partial^2},$the wave propagates in

physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

  1. $x$-direction

  2. $z$-direction

  3. $y$-direction

  4. $xz$ plane at an angle of $45^0$ between the $x$ and $z$direction

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Correct Option: A

According to the electromagnetic wave theory, light consists of electric and magnetic fields which are __________.

physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

  1. parallel to each other

  2. perpendicular to each other

  3. inclined at an angle of ${45}^{o}$ to each other

  4. none of these

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Correct Option: B
Explanation:

Light consists of electric and magnetic field that are perpendicular ${ 90 }^{ 0 }$ to each other.
APPOACH by example
Electric field inside plates. The magnetic field this given rise to via the displacement current is along the perimeter of the circle parallel to capauatates plates.

So B and E are perpendicular in this case.