Tag: the electromagnetic spectrum

Questions Related to the electromagnetic spectrum

Identify which of the following is NOT a source of visible light?

physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

  1. red-hot metal

  2. cool metal

  3. fluorescent bulb

  4. the Sun

  5. fire

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Correct Option: B
Explanation:

When the electrons in the atom are excited, for example by being heated, the additional energy pushes the electrons to higher energy orbits. When the electrons fall back down and leave the excited state, energy is re-emitted in the form of a photon.

Thus the hot objects release photons that have energies lying in the visible region. However photons from cool metal do not have energy enough to lie in visible region.

If a particular electromagnetic wave has the highest frequencies among the other electromagnetic waves then it should have the smallest

physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

  1. wavelengths

  2. speeds

  3. amplitudes

  4. energies

  5. periods

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Correct Option: A
Explanation:

Electromagnetic waves travel with constant speed equal to that of light  i.e  $v =c= constant$

For EM waves       $\lambda \times \nu = c =$ constant
Thus waves with highest frequency will have smallest wavelength.

Which of the following colors of light has the lowest frequency?

physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

  1. Yellow

  2. Violet

  3. Orange

  4. Blue

  5. Green

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Correct Option: C
Explanation:

The color with the lowest frequency corresponds to the longest wavelength, which is orange in this case.

Identify the waves with the largest wavelengths .

physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

  1. Radio

  2. Gamma Rays

  3. X-Rays

  4. Visible Light

  5. Infrared Radiation

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Correct Option: A
Explanation:

Order of wavelength from smallest to largest :

Gamma rays < X-rays < Visible light < Infrared Radiation < Microwaves < Radio waves
Thus radio waves has the largest wavelength.

Find out the wavelength of violet light which has a frequency of $7.5 \times 10^{14}Hz$ ?

physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

  1. $2.25\times 10^{23}m$

  2. $2.5\times 10^{5}m$

  3. $4\times 10^{-7}m$

  4. $7.5\times 10^{-7}m$

  5. $2.25\times 10^{7}m$

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Correct Option: C
Explanation:

Given :    $\nu = 7.5 \times 10^{14}$  Hz

Speed of violet light (EM wave)     $v = 3 \times 10^8$ m/s
Thus wavelength of violet light         $\lambda = \dfrac{v}{\nu}  = \dfrac{3 \times 10^8}{7.5 \times 10^{14}}  =4 \times 10^{-7}$ m

In an electromagnetic spectrum, identify which of the following lists are ordered from longest wavelength to shortest wavelength?

physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

  1. X ray, ultraviolet, visible light

  2. visible light, ultraviolet , X-ray

  3. ultraviolet, X-ray, visible light

  4. ultraviolet, visible light, X-ray

  5. X-ray, visible light, ultraviolet

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Correct Option: B
Explanation:

Decreasing order of wavelength :

 Visible light > ultraviolet > X-ray
Thus option B is correct.

Which of the following has the shortest wavelength? 

physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

  1. Red light

  2. Blue light

  3. Gamma rays

  4. X rays

  5. Radio waves

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Correct Option: C
Explanation:

Increasing order of wavelength :

Gamma rays < X-rays < Blue light < Red light < Radio waves
Thus gamma ray has the shortest wavelength.

The sun delivers $10^3\, Wm^{-2}$ of electromagnetic flux on the earth's surface. The total power that is incident on a roof of dimensions $6 \,m \times 30\, m$ is 

physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

  1. $1.8 \times 10^5\, W$

  2. $7.2 \times 10^5\, W$

  3. $0.9 \times 10^5\, W$

  4. $4.5 \times 10^5\, W$

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Correct Option: A
Explanation:

Given, electromagnetic flux $=10^3\, Wm^{-2}$
The area of roof $A= 6\, m \times 30\, m$
$=180 \, m^2$
The total power incident on roof
$P=10^3 \times 180$
$=1.8\times 10^5 \, W$

Clear images of soft tissues can be well studied using.

physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

  1. MRI

  2. X-rays

  3. Ultrasonics

  4. I.R rays

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Correct Option: A
Explanation:

MRI gives very detailed pictures of soft tissues like the brain

The method of using radio waves to cure some diseases are called

physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

  1. Physiotherapy

  2. Netratherapy

  3. Radiotherapy

  4. Radiometry

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Correct Option: C