SATHEE: Modern Physics 7 Question 27

Modern Physics 7 Question 27

28. In free space, the energy of electromagnetic wave in electric field is $U_{E}$ and in magnetic field is $U_{B}$ . Then

(a) $U_{E} = U_{B}$

(b) $U_{E} > U_{B}$

(d) $U_{E} = \frac{U_{B}}{2}$

(Main 2019, 9 Jan II)

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Solution:

Energy density of an electomagnetic wave in electric field,

$U_{E} = \frac{1}{2} ε_{0} \cdot E^{2}$

Energy density of an electromagnetic wave in magnetic field,

where, $E =$ electric field,

$U_{B} = \frac{B^{2}}{2 μ_{0}}$

$B$ =magnetic field,

$ε_{0} =$ permittivity of medium and

$μ_{0} =$ magnetic permeability of medium.

From the theory of electro-magnetic waves, the relation between $μ_{0}$ and $ε_{0}$ is

$c = \frac{1}{\sqrt{μ_{0} ε_{0}}}$

where, $c =$ velocity of light $= 3 \times 10^{8} m / s$

$and \frac{E}{B} = c$

Dividing Eq. (i) by Eq. (ii), we get

$\frac{U_{E}}{U_{B}} = \frac{\frac{1}{2} ε_{0} E^{2}}{\frac{1}{2} B^{2} \times \frac{1}{μ_{0}}} = \frac{μ_{0} ε_{0} E^{2}}{B^{2}}$

Using Eqs. (iii), (iv) and (v), we get

$\frac{U_{E}}{U_{B}} = \frac{c^{2}}{c^{2}} = 1$

Therefore, $U_{E} = U_{B}$

Modern Physics 7 Question 27

28. In free space, the energy of electromagnetic wave in electric field is $U_{E}$ and in magnetic field is $U_{B}$ . Then

Solution:

Engineering Preparation

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Modern Physics 7 Question 27

28. In free space, the energy of electromagnetic wave in electric field is UE and in magnetic field is UB. Then

Solution:

Engineering Preparation

Medical Preparation

NCERT Books & Solutions

Important Resources

Other Resources

Syllabus

Test Platform

Sample Mock Test

Mentorship

NCERT Exercise Video Solution

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28. In free space, the energy of electromagnetic wave in electric field is $U_{E}$ and in magnetic field is $U_{B}$ . Then