Physics

Electromagnetic Waves and Spectrum

659 Questions

Electromagnetic waves and spectrum questions test a candidate's understanding of radiation frequencies, wavelengths, and the properties of different rays like infrared, ultraviolet, and visible light. Concepts also cover practical applications in astronomy and the fundamental speed of light calculations. This physics topic appears regularly in general science sections of major competitive examinations.

UV rays propertiesElectromagnetic radiation frequencyWavelength identificationSpeed of light calculationsBlack body radiation

Electromagnetic Waves and Spectrum Questions

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

Which one of waves cannot be seen through electromagnetic spectrum?

  1. radio waves

  2. micro waves.

  3. infrared waves.

  4. ultraviolet waves.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Red, blue, green, yellow, orange colors are all part of electromagnetic spectrum that are visible to human eye.
The part which is not visible are UV, X-RAY, GAMMA RAY which have lower wavelength than visible light and infrared, radio waves have higher wavelength than visible.
Multiple choice physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

To distinguish between real gems and artificial gems a merchant may use which of the following radiations?

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

  3. X-rays

  4. Ultraviolet rays
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

To distinguish between real gems and artificial gems a merchant may use infrared radiations. A number of synthetic gems can be distinguished from their natural counterparts by differences in their infrared spectra.  

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

The frequencies of X-rays, $\gamma-rays$ and ultra violet rays are respectively $p, q$ and $r$, then

  1. $p > q, q > r$
  2. $p < q, q > r$
  3. $p < q, q < r$
  4. $p > q, q < r$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Increasing order of wavelengths as given below
$\gamma-rays < X-rays >$ ultravoilet rays
Frequency order
$\gamma-ray > X-rays >$ ultravoilet rays
$\Rightarrow q > p > r$
Thus, $q > p$
$q > r$
$p > r$.

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

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

  1. Visible light

  2. Infrared

  3. Microwave

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

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

  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 } } $
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In an electromagnetic wave, the relationship between the amplitudes of the electric field E0 and the magnetic field H0 is H0 = E0 * sqrt(epsilon / mu).

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

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

If the source of power $4kwW$ produces $10^20$ photons/second, the radiation belongs to the part of a spectrum called

  1. X rays

  2. Ultraviolet rays

  3. Microwaves

  4. Gamma rays
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The power of 4 kW (4000 W) with 10^20 photons per second implies each photon has an energy of 4000/10^20 = 4 x 10^-17 Joules. Converting this to electron volts (1 eV = 1.6 x 10^-19 J), we get approximately 250 eV, which falls into the X-ray region of the electromagnetic spectrum.

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

A wave has wavelength $50A^o$. Which of the following is a use of this wave?

  1. in detection of fracture in bones.

  2. in detection of planets

  3. in detection of water

  4. in detection of air
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

X-rays has a wavelength of $50 \mathring{A}$.
X-rays are used by doctors to see inside people. The machines are managed by a trained x-ray technician. They pass easily through soft tissues, but not so easily through bones.
Hence, they help in detecting fractures in bones.

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

Name the radiations of wavelength just shorter than $4\times 10^{-7}m$.

  1. Infraviolet

  2. Ultraviolet

  3. Infrared

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

The range of wavelength for visible light lies between, ${ 400 \ nm }<\lambda <{ 700 \ nm }$.

$\lambda $ just less than 400 nm is Ultraviolet.
$\lambda $ just greater than 700 nm is Infrared.

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

A wave has wavelength $50A^o$. State the speed of wave in vacuum.

  1. $3\times 10^8ms^{-1}$
  2. >$3\times 10^8ms^{-1}$
  3. <$3\times 10^8ms^{-1}$

  4. Insufficient information
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

X-rays has a wavelength of $50\ A^o$.
All electromagnetic radiation, of which radio waves and X-rays are examples, travels at the velocity of light, in a vacuum. The only difference between the two is that the frequency of X-rays is very much higher than radio waves.
Hence, X-rays travels at a speed of ${ 3\times 10 }^{ 8 }m/s$.