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Questions Related to physics

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

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-

  1. 3.5 m

  2. 5.5 m

  3. 7.5 m

  4. 9.5 m
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The wavelength of an electromagnetic wave is calculated using the relation lambda = c / f, where c is the speed of light in vacuum (3 times 10^8 m/s) and f is the frequency (40 MHz or 40 times 10^6 Hz). Dividing 3 times 10^8 by 40 times 10^6 yields 7.5 meters. The electric field amplitude is extra information not needed to find the wavelength.

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

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

  1. $3\times {10}^{9}m$
  2. $2.9\times {10}^{9}m$
  3. $3.6\times {10}^{6}m$
  4. $1.5\times {10}^{9}m$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Radio waves are electromagnetic waves that travel at the speed of light in vacuum, approximately 3 times 10^8 m/s. The distance traveled is the product of speed and time, which is (3 times 10^8 m/s) times 5.00 s = 1.5 times 10^9 meters.

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

The infra-red spectrum lies between:

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
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.
Multiple choice physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

X - ray beam can be deflected by 

  1. Magnetic field

  2. Electric field

  3. Both (a) & (b)

  4. None of these
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

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

  1. <p class="MsoNormal">Both assertion and reason are true and the reason is correct explanation of assertion.</p>

  2. <p class="MsoNormal"><span lang="EN-IN">Both assertion and reason are true and the reason is not the correct explanation of assertion.</p>

  3. Assertion is true but reason is false.

  4. Both assertion and reason are false.
Reveal answer Fill a bubble to check yourself
D Correct answer
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,

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

If a source of power $4\ kW$ produces $10^{20}$ photons/second, the radiation belongs to a part of the spectrum called:-

  1. $\gamma$-rays
  2. $X$-rays

  3. Ultraviolet rays

  4. Microwave
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$4\times { 10 }^{ 3 }={ 10 }^{ 20 }\times h\nu$ 

where $\nu=$frequency
$\nu =\cfrac { 4\times { 10 }^{ 3 } }{ { 10 }^{ 20 }\times 6.023\times { 10 }^{ -34 } } $
$\nu =6.64\times { 10 }^{ 16 }Hz$
This frequency lies in the spectrum of X-rays.

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

When accelerating voltage is increased from $10\ kV$ to $20\ kV$ in an X-ray tube, the gap between the wavelengths of $K _{\alpha}$ line and lowest end of continuous spectrum increases three times. The atomic number of the target element is:-

  1. $29$
  2. $27$
  3. $25$
  4. $23$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The shortest wavelength of the continuous spectrum is lambda_min = hc / eV. The gap between K-alpha and lambda_min is related to the accelerating voltage. Using Moseley's law and the given conditions, the atomic number Z can be solved.