2 Marks Questions

Question 12 Marks

When does a charge be source of origin of electromagnetic waves? How are the magnetic field and electric field mutually and with the transmission of wave related? Which physical quantity is same for waves of all parts of electromagnetic classification?

Answer

Accelerated electric charge can be a source of origin of electromagnetic waves. Electric and magnetic fields are mutually perpendicular in electromagnetic waves and also perpendicular to the direction of wave propagation. In air or vacuum, speed of all parts of electromagnetic spectrum classification is same which is $c=\frac{1}{\sqrt{\mu_0 \cdot \epsilon_0}}=3 \times 10^8 m / s$.

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Question 22 Marks

Write Maxwell's equations.

Answer

Maxwell's equations(i) $\oint \overrightarrow{ E } \cdot \overrightarrow{d A}=\frac{ Q }{\epsilon_0}$ (Gauss's law regarding electricity)(ii) $\oint \overrightarrow{ B } \cdot \overrightarrow{d A}=0 \quad$ (Gauss's law regarding magnetism)(iii) $\oint \overrightarrow{ E } \cdot \overrightarrow{ dl }=\frac{- d \phi_{ B }}{ dt }$ (Faraday's law)(iv) $\oint \overrightarrow{ B } \cdot \overrightarrow{d I }=\mu_0 I _{ C }+\mu_0 \in_0 \frac{d \phi_{ E }}{d t}$ (Ampere-Maxwell's law)

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Question 32 Marks

Write any four characteristics of electromagnetic wave.

Answer

(i) Electromagnetic waves do not require any material medium for their propagation.
(ii) Electromagnetic waves travel in a straight line.
(iii) The nature of electromagnetic waves is transverse.
(iv) The properties of the medium in which electromagnetic waves travel remain unchanged.

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Question 42 Marks

Write uses of X-rays.

Answer

Uses : (1) In radio astronomy, in amplifying the signals of very weak micro waves signals.
(2) Space communication, used in radio communication for long distances.
(3) Extensively used in medical science and micro surgeries.

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Question 52 Marks

A plane electromagnetic wave is propagating along Y -axis in vacuum. Write about the (i) ratio of magnitudes and (ii) directions of electric and magnetic fields.

Answer

(i) $E / B =c$, where $E =|\overrightarrow{ E }| ; B =|\overrightarrow{ B }|$ and $c=$ speed of light.
(ii) Electric and magnetic field vector $\vec{E}$ and $\vec{B}$ will be respectively along the Z -axis and X -axis. They will be perpendicular to the direction of transmission of wave.

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Question 62 Marks

The amplitude of the magnetic field part of a harmonic electromagnetic wave in vacuum is $B _0$$=510 nT$. What is the amplitude of the electric field part of the wave?

Answer

Given :$B _0=510 nT$. Amplitude of the magnetic = field part in vacuum = $=510 \times 10^{-9} T$.
Speed of the wave in vacuum =$3 \times 10^8 m / s$
Amplitude of the electric wave field part in vacuum = $ E _0$ = ?
We know that, for electromagnetic waves,
$c=\frac{ E _0}{B_0}$
or$E_0=c B_0$
On keeping the values,
$E_0=3 \times 10^8 \times 510 \times 10^{-9}$
$=153 V / m$

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Question 72 Marks

A radio can tune in to any station in the 7.5 MHz to 12 MHz band. What is the corresponding wavelength band?

Answer

Given : $\quad v_1=7.5 MHz$
$=7.5 \times 10^6 Hz$
$\begin{aligned} v_2 & =12 MHz \\ &
=12 \times 10^6 Hz\end{aligned}$
Speed of wave $c=3 \times 10^8 m / s$
Let corresponding wavelengths be $\lambda_1$ and $\lambda_2$.
$\therefore \quad \lambda_1=\frac{c}{v_1}=\frac{3 \times 10^{\circ}}{7.5 \times 10^6}=40 m$
Similarly,$\lambda_2=\frac{c}{v_2}=\frac{3 \times 10^8}{12 \times 10^6}=25 m$
Wavelength band station is from 25 m to 40 m .

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Question 82 Marks

A plane electromagnetic wave travels in vacuum along z-direction. What can you say about the directions of its electric and magnetic field vectors? If the frequency of the wave is 30 MHz, what is its wavelength?

Answer

We know that electromagnetic waves are transverse in nature. Here $\vec{E}$ and $\overrightarrow{ B }$ are located in xy plane and are mutually perpendicular.
Frequency of wave, $\quad v=30 MHz$
$=30 \times 10^6 Hz$
Speed of wave $=c=3 \times 10^8 m / s$
$\lambda=?$
We know, from $\quad c=v \lambda$,
$\therefore \quad \lambda=\frac{c}{v}=\frac{\text { Frequency of wave }}{\text { Speed of wave }}$
$\lambda=\frac{3 \times 10^8}{30 \times 10^6}=10 m$
Hence value of wavelength $=10 m$

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Physics 2 Marks Questions

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