Tag: electromagnetic spectrum

Questions Related to electromagnetic spectrum

Photons of an electromagneitc radiation has an energy $11keV$ each. To which region of electromagnetic spectrum does it belong?

  1. $X-ray\ region$

  2. $Ultra\ violet\ region$

  3. $infrared\ region$

  4. $visible\ region$


Correct Option: A
Explanation:

1 eV = (1.6 x 10^-19 coulomb) x (1 volt)

= 1.6 x 10^-19 joule

15 keV = 18 x 10^-16 J …..(a)

Given that photon energy = hf = 15 keV

hf = hc/lambda …… (b)

Now hc = (6.63 x 10^-34 J-sec) x (3 x 10^8 m/sec)

= 19.89 x 10^-28 J-m …..(c)

From (b), lambda = hc/15 keV and from (a) & (c)

Lambda = (19.89 x 10^-28 J-m)/(18 x 10^-16 J)

= 1.105 x 10^-12 m

= 0.01105 Angstrom, which is in the x-ray range

In which colour an yellow coloured dress would appear when viewed through a blue filter?

  1. yellow

  2. blue

  3. black

  4. green


Correct Option: C
Explanation:

Yellow light is a combination of red and green light. A dress appears yellow if it reflects red and green light to our eyes. In order to reflect red and green light, these two primary colors of light must be present in the incident light.
So, blue colored filter allows only blue color and absorbs all the remaining colors.
Therefore, yellow colored dress appears black.

The velocity of light is $3.0 \times {10^8}m{s^{ - 1}}$. Which value is closest to the wavelength in nanometres of a quantum of light with frequency of $8 \times {10^{15}}{s^{ - 1}}$?

  1. $3 \times {10^7}$

  2. $2 \times {10^{ - 25}}$

  3. $5 \times {10^{ - 18}}$

  4. $3.7 \times {10^1}$


Correct Option: A

Which of the following represents an infra-red wavelength?

  1. $10^{-4}cm$

  2. $10^{-5}cm$

  3. $10^{-6}cm$

  4. $10^{-7}cm$


Correct Option: A
Explanation:

Infrared radiation extends from the nominal red edge of the visible spectrum at $700nm$ to $1mm$.

and only $10^{-4} cm $  comes under this range.
The correct option is A.

An ultrasound equipment work at frequency:

  1.  Higher than $20,000 Hz $

  2.  Higher than $10,000 Hz $

  3.  Lower than 4420,000 Hz $

  4.  Lower than $10,000 H _2 $


Correct Option: A
Explanation:

Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. ultrasound devices operate with frequencies from 20000 Hz up to several gigahertz.

Select the correct statement from the following

  1. Electromagnetic waves cannot travel in vaccum

  2. Electromagnetic waves are longitudinal waves

  3. Electromagnetic waves are produced by charges moving with uniform velocity.

  4. Electromagnetic waves carry both energy and momentum as they propagate through space.


Correct Option: D

A standard radio broadcasting station has an assigned frequency between $535$ and $1605\ kHz$. The VHF(very high frequency) television stations (channels $2$ to $13$) have frequencies between $54$ and $216\ MHz$, while the UHF (u=ultra) stations (channels $14$ to $83$) have frequencies between $470$ and $890\ MHz$. What is the wavelength corresponding to each of the frequencies mentioned?

  1. $9.31, 0.368, 0.773$

  2. $1,39, 0.341, 1.66$

  3. $1.39, 0.638, 0.337$

  4. $None of these$


Correct Option: B

One requires 2 IeV of energy to dissociate a carbon molecule into carbon and oxygen atoms. The minimum frequency of the appropriate electromagnetic radiation to achieve the dis-acceleration lines is 

  1. visible region

  2. interacted region

  3. ultraviolet region

  4. microwave region


Correct Option: C
Explanation:

$E = 21 eV = 21 \times 1.6 \times 10^{-19}$

$\alpha = \dfrac{21 \times 1.6 \times 10^{-19}}{6.62 \times 10^{-34}} = 5.07 \times 10^{15} Hz$
This is belongs ultraviolet region

Which one of the following is not a electromagnetic waves?

  1. X - rays

  2. Gamma rays

  3. cathode rays

  4. Infrared rays


Correct Option: C

Neglecting reduced mass effects, what optical transition in the ${ He }^{ + }$ spectrum would have the same wavelength as the first Lyman transition of hydrogen ($n=2$ to $n=1$)

  1. $n = 2$ to $n = 1$

  2. $n = 3$ to $n = 1$

  3. $n = 4$ to $n = 2$

  4. None of the above


Correct Option: C