Tag: observing space: telescopes

Questions Related to observing space: telescopes

The wavelengths for the light of red and blue colours are roughly $7.8\times 10^{-7}m$ and $4.8\times 10^{-7}m$ respectively. Which colour has the greater speed in glass?

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. Red light

  2. Violet light

  3. Yellow light

  4. All colors have same speed

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Correct Option: A
Explanation:

When travelling through a medium, the frequency of light doesn't change. Hence, red light having the maximum wavelength will travel fastest through glass as speed of light is given by $v=f\lambda$ where; $f$ is the frequency and $\lambda$ is the wavelength of light travelling at speed $v$.

What is the speed of Light $c$?

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. $c=3\times 10^{-8} m s^{-1}$

  2. $c=3\times 10^8 km s^{-1}$

  3. $c=3\times 10^8 mm s^{-1}$

  4. $c=3\times 10^8 m s^{-1}$

Show answer
Correct Option: D
Explanation:

The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. Its value is exactly $299792458$ meters per second.
That is, $c=3\times { 10 }^{ 8 }m/s$.

The electromagnetic waves do not transport

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. energy

  2. charge

  3. momentum

  4. information

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Correct Option: B
Explanation:

$Answer:-$ B

EM waves carry energy (light ), momentum (can be seen by photoelectric experiment) and information (like radiowaves ) but does'nt carry charge. 

In which form does the Light propagates?

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. Electric waves

  2. Magnetic waves

  3. Electromagnetic waves

  4. Sound wave

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Correct Option: C
Explanation:

Electromagnetic waves are waves which can travel through the vacuum of outer space.light waves are examples of electromagnetic waves.
so,Light propagates in the form of electromagnetic waves.

As speed decreases, if we change medium of electromagnetic waves from air to water, frequency

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. also decreases.

  2. also increases.

  3. remains same.

  4. may increase or decrease.

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Correct Option: C
Explanation:

As speed decreases, if change medium of electromagnetic wave from air to water, frequency remains same.

As we go from one medium to another the frequency stays same, but the wavelength changes. Change in speed is proportional to change in wavelength.

A plane electromagnetic wave of angular frequency ${ mm }^{ 2 }$ propagates in a poorly conducting medium of conductivity $\sigma $ and relative permittivity $\epsilon $ Find the ratio of conduction current density and displacement current density in the medium.

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. ${ \epsilon \epsilon } _{ 0 }\omega /\sigma $

  2. $\sigma /{ \epsilon \epsilon } _{ \sigma }\omega $

  3. $\omega /{ \sigma \epsilon } _{ 0 }\omega $

  4. $\omega \sigma /{ \epsilon } _{ 0 }\epsilon $

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Correct Option: A

Which among the four options is not correct ion given situation ? A charged particle oscillates about its mean equilibrium position with a frequency of $10^9\, Hz.$ The electromagnetic waves produced 

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. Will have frequency of $10^9\, Hz.$

  2. Will have frequency of $2\times 10^9\, Hz.$

  3. Will have wavelength of $0.3\,m.$

  4. Fall in the region of radio waves

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Correct Option: C

An electromagnetic wave with frequency $\omega$ and wavelength $\lambda$ travels in the $+y$ direction. Its magnetic field is along $-x$ axis. The vector equation for the associated electric field (of amplitude E_0)is :

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. $ \vec { E } = E _0 \cos \left(\omega t -\dfrac{2\pi}{\lambda}y\right)\hat{x}$

  2. $\vec{ E } = -E _0 \cos \left(\omega t +\dfrac{2\pi}{\lambda}y\right)\hat{x}$

  3. $-\vec{ E } = E _0 \cos \left(\omega t +\dfrac{2\pi}{\lambda}y\right)\hat{z}$

  4. $\vec { E } = E _0 \cos \left(\omega t -\dfrac{2\pi}{\lambda}y\right)\hat{z}$

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Correct Option: A

Electro magnetic waves are transverse in nature as is evident by

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. polarization

  2. interference

  3. reflection

  4. deffraction

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Correct Option: A
Explanation:

Electromagnetic waves are transverse in nature as is evident by polarization interference and diffraction explain the wave nature of light or $EM$ waves polarization is the phenomenon by which we restrict the vibration of wave in a particular direction perpendicular to direction of $W$ are propagation. So, it explains the transverse nature of $EM$ waves.

Answer :- polarization.

The maximum kinetic energy of electron if wavelength of incident electromagnetic wave is $260 \,nm$ and cut-off wavelength is $380 \,nm$ given $hc = 1237 \,nm-eV$ is

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. $1.5 \,eV$

  2. $6.4 \,eV$

  3. $10 \,eV$

  4. None of these

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Correct Option: A
Explanation:

We know 
$KE _{max} = \dfrac{hc}{\lambda} - \dfrac{hc}{\lambda _0} $
$= \dfrac{1237 \, nm. eV}{260 \, nm} - \dfrac{1237 \, nm . eV}{380 \, nm}$
$= 1.5 eV$