One requires 11 \(eV\) of energy to dissociate a carbon monoxide molecule into carbon and oxygen atom. The minimum frequency of the appropriate electromagnetic radiation to achieve the dissociation lines in

1

(a)

visible region

(b)

infrared region

(c)

ultraviolet region

(d)

microwave region

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

1

(a)

\(\overset { \rightarrow }{ { E }_{ r } } ={ E }_{ 0 }\overset { \wedge }{ i } cos(kz-wt)\quad \)

(b)

\(\overset { \rightarrow }{ { E }_{ r } } ={ E }_{ 0 }\overset { \wedge }{ i } cos(kz+wt)\quad \)

(c)

\(\overset { \rightarrow }{ { E }_{ r } } ={ -E }_{ 0 }\overset { \wedge }{ i } cos(kz+wt)\quad \)

(d)

\(\overset { \rightarrow }{ { E }_{ r } } ={ -E }_{ 0 }\overset { \wedge }{ i } sin(kz+wt)\quad \)

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

1

(a)

\(\overset { \rightarrow }{ E } \)

(b)

\(\overset { \rightarrow }{ B } \)

(c)

\(\overset { \rightarrow }{ B } \times \overset { \rightarrow }{ E } \)

(d)

\(\overset { \rightarrow }{ E } \times \overset { \rightarrow }{ B } \)

The radiation force on the roof is 

1

(a)

\(2.67\times { 10 }^{ -4 }N\)

(b)

\(5.34\times { 10 }^{ -4 }N\)

(c)

\(2.33\times { 10 }^{ -4 }N\)

(d)

\(1.33\times { 10 }^{ -4 }N\)

Give difference between displacement and conduction current

1

(a)

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.

Is the steady electric current the only source of a magnetic field? Justify your answer.

1

(a)

No, the displacement current also produces magnetic field between two plates of capacitor during charging and discharging of capacitor

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

1

(a)

The quantity \({ \in }_{ 0 }\frac { { d\phi }_{ E } }{ dt } \) 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.

A capacitor has been charged by a DC source. what are the magnitudes of conduction and displacement current, when it is fully charged?

1

(a)

When the capacitor is fully charged. let q be the charge on the plate of the capacitor. which is constant.
Electric flux through the plates of capacitor
\({ \phi }_{ E }=q/{ \in }_{ 0 }=a\quad constant\)
Displacement current,
\({ I }_{ D }={ \in }_{ 0 }\frac { { d\phi }_{ E } }{ dt } ={ \in }_{ 0 }\frac { d\left( q/{ \in }_{ 0 } \right) }{ dt } =0\)
Let C be the capacity of capacitor and V be the pot. diff. between two plates of the capacitor when the capacitor is fully charged, then q = CV
Conduction current, 
\(I=\frac { d(CV) }{ dt } =C\frac { dv }{ dt } =0\) as V is constant, when capacitor is fully charged.

Write down Maxwell's equation for the steady electric field.

1

(a)

(i) \(\oint _{ s }^{ }{ \overset { \rightarrow }{ E } } .\overset { \rightarrow }{ ds } =\frac { q }{ { \epsilon }_{ 0 } } \)
(ii) \(\oint { \overset { \rightarrow }{ E } .\overset { \rightarrow }{ dt } =0 } \)

Why is the Quantity \({ \varepsilon }_{ 0 }d\Phi _{ E }/dt\) called the displacement current?

1

(a)

Due to change in electric field

What is the ratio of speed of infrared and ultraviolet rays in vacuum?

1

(a)

Same as velocity of light

An electromagnetic wave consists of oscillating electric and magnetic fields. What is the phase relationship between these oscillations?

1

(a)

90 degree