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Published on: 27/08/2019
Electromagnetic Waves
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Questions + Answers key
Take MCQ Physics Test
1.
The radiation force on the roof is
\(2.67\times { 10 }^{ -4 }N\)
\(5.34\times { 10 }^{ -4 }N\)
\(2.33\times { 10 }^{ -4 }N\)
\(1.33\times { 10 }^{ -4 }N\)
2.
If \(\overset { \rightarrow }{ E } \) and \(\overset { \rightarrow }{ B } \) represent electric and magnetic field vectors of the electromagnetic wave the direction of propagation of electromagnetic wave is along
\(\overset { \rightarrow }{ E } \)
\(\overset { \rightarrow }{ B } \)
\(\overset { \rightarrow }{ B } \times \overset { \rightarrow }{ E } \)
\(\overset { \rightarrow }{ E } \times \overset { \rightarrow }{ B } \)
3.
A linearly polarized electromagnetic wave given as \(E={ E }_{ 0 }\overset { \wedge }{ i } cos \ (kz-wt)\) incident wall at \(z=a\) . Assuming that the material of the wall os optically inactive, the reflected wave will be given as
\(\overset { \rightarrow }{ { E }_{ r } } ={ E }_{ 0 }\overset { \wedge }{ i } cos(kz-wt)\quad \)
\(\overset { \rightarrow }{ { E }_{ r } } ={ E }_{ 0 }\overset { \wedge }{ i } cos(kz+wt)\quad \)
\(\overset { \rightarrow }{ { E }_{ r } } ={ -E }_{ 0 }\overset { \wedge }{ i } cos(kz+wt)\quad \)
\(\overset { \rightarrow }{ { E }_{ r } } ={ -E }_{ 0 }\overset { \wedge }{ i } sin(kz+wt)\quad \)
4.
An electromagnetic wave consists of oscillating electric and magnetic fields. What is the phase relationship between these oscillations?
5.
What is the ratio of speed of infrared and ultraviolet rays in vacuum?
6.
Why is the Quantity \({ \varepsilon }_{ 0 }d\Phi _{ E }/dt\) called the displacement current?
7.
Write down Maxwell's equation for the steady electric field.
8.
A capacitor has been charged by a DC source. what are the magnitudes of conduction and displacement current, when it is fully charged?
9.
Why is the quantity \({ \in }_{ 0 }\frac { { d\phi }_{ E } }{ dt } \) called the displacement current? where \({ d\phi }_{ E }/dt\) is the rate of change of electric flux linked with a region or space
10.
Is the steady electric current the only source of a magnetic field? Justify your answer.
11.
Give difference between displacement and conduction current
1.
(a)
\(2.67\times { 10 }^{ -4 }N\)
2.
(a)
\(\overset { \rightarrow }{ E } \)
3.
(b)
\(\overset { \rightarrow }{ { E }_{ r } } ={ E }_{ 0 }\overset { \wedge }{ i } cos(kz+wt)\quad \)
4.
90 degree
5.
Same as velocity of light
6.
Due to change in electric field
7.
\(\text { (i) } \oint_s \vec{E} \cdot \overrightarrow{d s}=\frac{q}{\epsilon_0}\)
\(\text { (ii) } \oint \vec{E} \cdot \overrightarrow{d t}=0\)
8.
Electric flux through plates of capacitor, \(\phi_E=\frac{q}{\varepsilon_0}\).
where, charge, q= constant (as the capacitor is fully charged)
Displacement current, \(I_d=\varepsilon_0 \frac{d \phi_E}{d t}=\varepsilon_0 \frac{d\left(\frac{q}{\varepsilon_0}\right)}{d t}=0\)
Conduction current, \(I_c=C \frac{d V}{d t}=0\) (as voltage becomes constant when the capacitor becomes fully charged).
9.
The quantity \(\epsilon_0 \frac{d \phi_E}{d t}\) has the dimension of current and this current exists in a region between the two plates of the capacitor when a displacement of charges occurs there. i.e., during charging and discharging of the capacitor.
10.
No, the displacement current also produces magnetic field between two plates of capacitor during charging and discharging of capacitor
11.
conduction current is due to flow of electrons in the circuit. It exists even if the flow of electrons is at uniform rate. Displacement current is due to the time-varying electric field. It does not exist under steady condition.
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