Physics

Electromagnetic Waves and Spectrum

670 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

Electromagnetic radiation is emitted by

  1. X-rays

  2. Ultrasonic

  3. Electrons

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

Electrons are responsible for emission of most Electromagnetic radiation because they have low mass, and therefore are easily accelerated by a variety of mechanisms.  

Multiple choice

Infrared radiation has the ……….. wave length.

  1. longest

  2. strongest

  3. shortest

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

Infrared radiation has wavelengths longer than visible light but shorter than microwaves. Among the choices provided, it is characterized by its relatively long wavelength.

Multiple choice physics optoelectronic devices resistance and temperature

A laser operates at a frequency of $3\times 10^{14} H _z$ and has an aperture of $1cm$. The radii spread of the beam is 

  1. $10^{-3}$ radian
  2. $5\times 10^{-3}$ radian
  3. $10^{-4}$ radian
  4. $10^{-2}$ radian
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Due to non ideality in monochromatic nature of a laser, there exists some spread $\theta$, 


$\theta =\dfrac { \lambda  }{ \pi r } =\dfrac { c }{ \pi fr } $

$\theta={ 10 }^{ -4 } \ radian$

Multiple choice physics optoelectronic devices resistance and temperature

Wavelength of a laser beam can be used as a standard of:

  1. time

  2. temperature

  3. angle

  4. length
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Wavelength of a laser beam can be used as a standard of  length because wavelength is considered as the measure of length of the wave.


Multiple choice physics wave motion reflection of waves

The wavelength of the first line of Lyman series is $\lambda$. The wavelength of the first line in Paschen series is ________.

  1. $108/7$
  2. $27/5$
  3. $7/108$
  4. $5/27$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Formula for Lyman series is:
Where, n = 2,3,4,5,.....
Where, R = Rydbergg constant,
$\dfrac{1}{\lambda}=R\left(\dfrac{1}{1^2}-\dfrac{1}{2^2}\right)$ and
 Paschen series in $\lambda _1$,
$\Rightarrow \dfrac{1}{\lambda _1}=R\left(\dfrac{1}{3^2}-\dfrac{1}{4^2}\right)$

$\Rightarrow \dfrac{\lambda _1}{\lambda}=\dfrac{\dfrac{3}{4}}{\dfrac{7}{16\times 9}}$

$\Rightarrow \lambda _1=\dfrac{3}{4}\times \dfrac{16\times 9}{7}\lambda$

$\Rightarrow \lambda _1=\dfrac{108}{7}\lambda$.

Multiple choice physics oscillations and waves huygen's wave theory refraction of water waves reflection and refraction at plane surfaces theories on light

The higher the frequency of light?

  1. The longer (larger) its wavelength.

  2. The shorter (smaller) its wavelength.

  3. The greater its velocity in a vacuum.

  4. The redder it will be
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The relationship between frequency (f) and wavelength (lambda) is given by c = f * lambda, where c is the speed of light. Therefore, frequency and wavelength are inversely proportional. As frequency increases, wavelength must decrease.

Multiple choice physics oscillations and waves huygen's wave theory refraction of water waves reflection and refraction at plane surfaces theories on light

An observer is moving with half the speed of light towards stationary microwave source emitting waves at frequency 10 GHz. What is the frequency of the microwave measured by the observer ?(speed of light = $3 \times10^{8} \ ms^{-1}$)

  1. 15.3 GHz

  2. 10.1 GHz

  3. 12.1 GHz

  4. 17.3 GHz
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Doppler effect in light ( speed of observer is not very small compared to speed of light )
$f^{1} = \sqrt{\dfrac{1+V/C}{1-V/C}} f _{source} = \sqrt{\dfrac{1+1/2}{1-1/2}} (10\ GHz)$
$=17.3\ GHz$


Multiple choice physics oscillations and waves huygen's wave theory refraction of water waves reflection and refraction at plane surfaces theories on light

Two monochromatic light source, A and B , emit the same number of photons wavelength of A is $ \lambda _A = 400 nm $, and that of $ \lambda _B =600 nm $. the power of radiated

  1. equal to that of source A

  2. less than that source A

  3. greater than that of source A

  4. can not be compared to that source A using the available data
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice physics oscillations and waves huygen's wave theory refraction of water waves reflection and refraction at plane surfaces theories on light

The wavelength of a monochromatic light in vacuum is $\lambda$. If travels from vacuum to a medium of absolute refractive index $\mu$. The ratio of wavelength of the incident and refracted wave is

  1. $\mu^2 : 1$

  2. 1 : 1
  3. $\mu$ : 1
  4. 1:$\mu$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

${ \left{ \mu \lambda  \right}  } _{ vacuum }={ \left{ \mu \lambda  \right}  } _{ medium }\ \Rightarrow \dfrac { { \lambda  } _{ i } }{ { \lambda  } _{ r } } =\dfrac { \mu  }{ 1 } \ \therefore \ Ratio\ is\ \mu :1$

Multiple choice physics oscillations and waves huygen's wave theory refraction of water waves reflection and refraction at plane surfaces theories on light

The frequency of light of wave length 5000 $\mathring {A}$ is

  1. $1.5 \times 10^5 Hz$
  2. $6 \times 10 Hz$
  3. $6 \times 10^{14} Hz$
  4. $7.5 \times 10^{15} Hz$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Answer is B.

The relation between the velocity of light, frequency and wavelength is given as v = f$\lambda $.
The velocity of light v = $3 \times 10^{8}m/s$.
So, f = $v/\lambda $ = $3 \times 10^{8}m/s / 5000\mathring{A}$ = $6 \times 10^{14} Hz$.
Hence, the frequency of the light is $6 \times 10^{14} Hz$.