Tag: the nature of light

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Questions Related to the nature of light

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

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

  1. $6m^{-1}$

  2. $3m^{-1}$

  3. $2m^{-1}$

  4. $0.5m^{-1}$
Reveal answer Fill a bubble to check yourself
C Correct answer
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
Multiple choice physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

Wavelength of light in different media are proportional to:

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The speed of light in a medium is given by v = f * lambda. Since frequency (f) remains constant when light moves between media, the wavelength (lambda) is directly proportional to the speed of light (v) in that medium.

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

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

  1. Faraday's law of induction

  2. Modified Ampere's law

  3. Gauss's law of electricity

  4. Gauss's law of magnetism
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

In Maxwell's velocity distribution curve area under the graph 

  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
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

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

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

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

Which of the following conclusion can be drawn from the result $\oint \bar{B}\cdot d\bar{A}=0$

  1. Magnetic field is zero everywhere

  2. Magnetic monopole cannot exist

  3. Magnetic lines of force do not intersect each other

  4. A current produces magnetic field
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Flux of certain closed surface is zero and so it tells that net magnetic charge is equal to zero. This is possible when there are two equal and opposite poles.

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

Which of the following effects could not be explained by Maxwell's electromagnetic wave theory?

  1. Photoelectric effect

  2. Compton effect

  3. Raman effect

  4. All of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

  1. Photoelectric effect was discovered by heinrich Rudoy Hertz.
  2. Compton effect was discovered by Aethur Holl Compton.
  3. Raman effect was discovered by Sir Chandrasekhar Venbata Ram. 
      So, none of these effect was discovered by Maxwell.

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

A parallel plate capacitor having plate area A and plate separation $d$ is connected to a battery of emf $\varepsilon$ and internal resistance $R$ at $t=0$. Consider a plane surface of area $\dfrac{A}{2}$, parallel to the plates and situated symmetrically between them. Find the displacement current through this surface as a function of time?

  1. $\dfrac {-\varepsilon}{2R} \ \ \ e^{\dfrac{-td}{\varepsilon AR}}$

  2. $\dfrac {2\varepsilon}{R} \ \ \ e^{\dfrac{-td}{\varepsilon AR}}$

  3. $\dfrac {5\varepsilon}{2R} \ \ \ e^{\dfrac{-td}{4 \varepsilon AR}}$

  4. $\dfrac {\varepsilon}{2R} \ \ \ e^{\dfrac{-td}{4\pi \varepsilon AR}}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The displacement current in a charging capacitor is equal to the conduction current in the circuit. The current in an RC circuit is I(t) = (epsilon/R) * e^(-t/RC). Since the surface area A/2 is parallel to the plates, it intercepts half the electric flux, leading to a factor of 1/2.