Tag: electromagnetic waves

Questions Related to electromagnetic waves

What name is given to the type of astronomy having the following characteristics.
I. It is carried out in the waveband $300$nm to $10$nm.
II. The atmosphere is opaque to the incoming radiation from space
III. Observations are to be carried out from above the earth's atmosphere.

physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

  1. X-ray astronomy

  2. Ultra-violet astronomy

  3. Infra-red astronomy

  4. Gamma ray astronomy

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Correct Option: B
Explanation:
Ultra-violet astronomy is carried out in waveband of $10nm-300nm$ in which is above earth's atmosphere.

A beam of ultraviolet light of all wavelengths passes through hydrogen gas at room temperature, in the $x-$direction. Assume that all photons emitted due to electron transitions inside the gas emerge in the $y-$direction. Let $A$ and $B$ denote the lights emerging from the gas in the $x-$ and $y-$directions respectively. Then,

physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

  1. some of the incident wavelengths will be absent in $A$

  2. only those wavelengths will be present in $B$ which are absent in $A$

  3. $B$ will contain some visible light

  4. $B$ will contain some infrared light

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Correct Option: A,C,D
Explanation:

$A, C, D$

The magnetic field in a plane electromagnetic wave is given by $=2\times10^{-7} \sin(0.5\times 10^3 x+1.5\times10^{11}t)$. This electromagnetic wave is

physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

  1. Visible light

  2. Infrared

  3. Microwave

  4. Radiowave

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Correct Option: C
Explanation:

The magnetic field in a plane of electromagnetic  wave is given by

$B=2\times 10^{-7}sin(0.5\times 10^3x+1.5\times 10^{11}t)$
from the above, $K=0.5\times 10^3=$ propagation constant
$K=\dfrac{2\pi}{\lambda}$ where, $\lambda=$ wavelength of wave
$\lambda=\dfrac{2\times 3.14}{0.3\times 10^3}$
$\lambda=1.256\times 10^{-2}m$
$\lambda=1.256 cm$
The electromagnetic wave is Microwave radiation in spectrum.

In the EM wave , the amplitude of magnetic field $ H _o $ and the amplitude of electric field $ E _o $ at a place D are related as:

physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

  1. $ H _o = E _o $

  2. $ H _ o=\frac { E _ o }{ c } $

  3. $ H _ o=\quad E _ o\quad \sqrt { \frac { \mu _ o }{ \varepsilon _ o } } $

  4. $ H _ o=\quad E _ o\quad \sqrt { \frac { \varepsilon _ o }{ \mu _ o } } $

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Correct Option: D

A plane electromagnetic wave of frequency $40 MHz$ travels in free space in the X-direction. At some point and at some instant, the electric field $\vec{E}$ has its maximum value of $750N/C$ in Y-direction. The wavelength of the wave is-

physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

  1. 3.5 m

  2. 5.5 m

  3. 7.5 m

  4. 9.5 m

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Correct Option: A

Find the distance (in meters) traveled by a radio wave in $5.00$ seconds?

physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

  1. $3\times {10}^{9}m$

  2. $2.9\times {10}^{9}m$

  3. $3.6\times {10}^{6}m$

  4. $1.5\times {10}^{9}m$

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Correct Option: A

The infra-red spectrum lies between:

physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

  1. radio wave and micro-wave region

  2. the micro-wave and visible region

  3. the visible and ultra violet region

  4. the ultra violet and the X-ray region

Show answer
Correct Option: B
Explanation:
                        Light comparison
Name            wavelength                   Frequency
visible          $400nm-700nm$        $790THz-430THz$
Infrared        $700nm-1mm$           $430THz-300GHz$
Microwave   $1mm-1$meter           $300GHz-300MHz$
Therefore the infrared spectrum lies between (B), the micro-wave & visible region.

X - ray beam can be deflected by 

physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

  1. Magnetic field

  2. Electric field

  3. Both (a) & (b)

  4. None of these

Show answer
Correct Option: D
Explanation:

$X-$rays aren't deflected by electrons and magnetic fields because $x-$rays do not carry and charge. They are electro-magnetic radiations and therefore cannot be deflected by electronic or any magnetic fields.

Assertion :- Microwave communication is preferred over optical communication. 
Reason :- Microwaves provide large number of channels and band width compared to optical signals. 

physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

  1. Both assertion and reason are true and the reason is correct explanation of assertion.

  2. Both assertion and reason are true and the reason is not the correct explanation of assertion.

  3. Assertion is true but reason is false.

  4.  Both assertion and reason are false.

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Correct Option: D
Explanation:

Both assertion and reason are false.

Optical communication is always preferred over microwave

communication also Bandwidth and number of channels are more in case of optical communication.

Hence both statements are false.
so the  correct option is D,

_____ light creates intense heating when it is incident on a substance

physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

  1. visible

  2. ultra violet

  3. Infra red

  4. X-ray

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Correct Option: C