Tag: the electromagnetic spectrum

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Questions Related to the electromagnetic spectrum

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

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

  1. red-hot metal

  2. cool metal

  3. fluorescent bulb

  4. the Sun

  5. fire
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

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

  1. wavelengths

  2. speeds

  3. amplitudes

  4. energies

  5. periods
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

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

  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. $2.25\times 10^{7}m$
Reveal answer Fill a bubble to check yourself
C Correct answer
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

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

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

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Decreasing order of wavelength :

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

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

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 

  1. $1.8 \times 10^5\, W$
  2. $7.2 \times 10^5\, W$
  3. $0.9 \times 10^5\, W$
  4. $4.5 \times 10^5\, W$
Reveal answer Fill a bubble to check yourself
A Correct answer
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
$P=10^3 \times 180$
$=1.8\times 10^5 \, W$