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Physics 1 Marks Question

Electromagnetic Waves · Rajasthan Board (RBSE) STD 12 Science (Rajasthan - English Medium). 47 questions.

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Question 11 Mark
Write the name of any three waves (radiations) produced in the electromanetic spectrum.
Answer
(i) r-rays, (ii) X-rays, (iii) Ultraviolet rays.
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Question 21 Mark
Obtain ratio of speed between lights of wavelength 5000 À and 8000 A in vacuum.
Answer
Ratio is 1 because in vacuum, the speed is independent of wavelengths.
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Question 31 Mark
In long range transmission, why micro waves are better carrier than radio waves?
Answer
In long range transmission, micro waves are better carrier than radio waves because their wavelength is very less as compared to radio waves. Due to this, during obstruction, they suffer minimum deviation and can be sent directly towards the aim.
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Question 51 Mark
On a metallic target, when high energy electrons are struck, electromagnetic waves are produced. Name these waves.
Answer
X-rays
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Question 61 Mark
Which characteristic of electromagnetic waves it is assumed that light waves are electromagnetic?
Answer
Speed of light waves is equal to the speed of electromagnetic waves.
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Question 81 Mark
Out of the following, which radiation has least frequency?Gamma rays, Infrared rays, X-rays, Blue light.
Answer
Infrared rays.
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Question 91 Mark
A plane electromagnetic wave is travelling along Z-axis in vacuum. What can you say about the electric field and magnetic field vectors?
Answer
Electric field vector E and magnetic field vector B are perpendicular to the direction of propagation of wave and are also mutually perpendicular to each other. Since here the wave is travelling along the Z-axis, so vectors E and B are in the plane X-Y and mutually perpendicular to each other.
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Question 121 Mark
Define displacement current.
Answer
Current generated due to electric field or electric flow variation between plates of capacitor is known as displacement current.
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Question 131 Mark
Write the name of that part of electromagnetic spectrum with which electromagnetic waves of following wavelength associated. Write them in descending order of wavelength.
(a) $\lambda_1$ : used in treatment of muscular strains
(b) $\lambda_2$ : used in radio transmission
(c) $\lambda_3$ : used to detect fracture in bones
(d) $\lambda_4:$ are absorbed by ozone layer in the atmosphere
Answer
(a) $\lambda_1 \rightarrow$ Infrared radiations
(b) $\lambda_2 \rightarrow$ Radio waves
(c) $\lambda_3 \rightarrow X$-rays
(d) $\lambda_4 \rightarrow$ Ultraviolet radiations $ \lambda_2>\lambda_1>\lambda_4>\lambda_3 $
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Question 141 Mark
Write principle for producing the electromagnetic waves.
Answer
Accelerated charge produces electric and magnetic fields which change both with time and place. These changeable electric and magnetic fields give rise to electromagnetic waves.
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Question 151 Mark
(a) Write Gauss's law of magnetism in terms of Maxwell equation.(b) Write value of $\frac{1}{\sqrt{\mu_0 \epsilon_0}}$.
Answer
(a) $\oint \overrightarrow{ B } \cdot \overrightarrow{d A}=0$(b) $c$ or $3 \times 10^8 m / s$.
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Question 161 Mark
Write name of that part of electro-magnetic spectrum whose wavelength is $10^{-2} m$ and write its one use also.
Answer
Micro wave: It is used in microwave oven and communication system.
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Question 171 Mark
What is the frequency of electromagnetic waves originated from oscillating electrical circuits?
Answer
Radio waves $\left(3 \times 10^9 Hz\right.$ to $\left.3 \times 10^4 Hz\right)$
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Question 181 Mark
Which part of electromagnetic spectrum is used in the working of radar?
Answer
Radar works in very minute micro wave part of the electromagnetic spectrum. Its wavelength is from 10 m to 0.3 m.
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Question 201 Mark
Write the following in decreasing order of wavelengths:X-rays, Radio waves, Sky light, Infrared light.
Answer
Radio waves, Infrared light, Sky light, X-rays
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Question 211 Mark
Whose wavelength is minimum among the following:Micro waves, Ultraviolet radiation and X-rays.
Answer
X-rays
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Question 241 Mark
Write name of that electromagnetic radiation whose wavelength is in the range of $10^{-2}$. Write one use of these radiation.
Answer
Micro waves (Long distance communication).
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Question 251 Mark
Write the name of the electromagnetic wave that is used to study crystal structure of solids.
Answer
X -rays $\left(10^{16}\right.$ to $\left.10^{20} Hz\right)$.
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Question 261 Mark
Which electromagnetic waves are produced by the Hertz experiment and what is the range of their wavelength?
Answer
Short Radio waves and their wavelength is of the order of 1m.
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Question 271 Mark
Write expression for speed of electro-magnetic waves in a medium.
Answer
$v=\frac{1}{\sqrt{\mu \epsilon}}$
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Question 291 Mark
Write following radiations in descending order of wavelengths:X-rays, Radio waves, Ultraviolet waves, Gamma rays.
Answer
Radio waves, Ultraviolet waves, X-rays, Gamma rays.
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Question 321 Mark
Frequency of oscillation of electric field vector of any electromagnetic wave is $5 \times 10^{14} Hz$. What is the frequency of oscillation of corresponding magnetic field? To which part of electromagnetic spectrum is it associated?
Answer
$5 \times 10^{14} Hz$, Visible light part.
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Question 331 Mark
Express the speed of transmission of electromagnetic wave in terms of peak values of electric and magnetic fields.
Answer
$c=\frac{E_0}{B_0}$
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Question 341 Mark
What are the main sources of electro- magnetic waves?
Answer
Electric field $\vec{E}$ is produced due to change in magnetic field $\vec{B}$ with time and similarly, magnetic field $\vec{B}$ is produced due to change in electric field $\vec{E}$ with time. In this way, change of these field vectors with time works as a source for each other. Hence the main sources of electromagnetic waves are magnetic field $\vec{B}$ and electric field $\vec{E}$.
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Question 351 Mark
Name electromagnetic waves which are: (a) Helpful in relaxing the muscles. (b) Absorbed by the ozone layer in the atmosphere.
Answer
(a) Infrared rays,(b) Ultraviolet rays.
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Question 361 Mark
Can light waves travel in vacuum? Give reason also.
Answer
Since light waves are electromagnetic waves, hence they do not need any material medium for their propagation.
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Question 371 Mark
Write mathematical expression for Ampere- Maxwell's law.
Answer
$\oint \overrightarrow{ B } \cdot \overrightarrow{d l}=\mu_0\left( I _c+ I _d\right)$where displacement current $I _d=\epsilon_0\left(\frac{d \phi_{ E }}{d t}\right)$ and $I _c=$ conduction current.
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Question 391 Mark
By what speed do electromagnetic waves travel in vacuum?
Answer
Electromagnetic waves travel with the speed of light.
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Question 411 Mark
(a) In space, magnitude of electric field vector (E) at any point is $9.3 V / m$. Calculate the magnitude of magnetic field vector (B) at this point.
(b) Out of ultraviolet, infrared and X-rays, whose wavelength is maximum?
Answer
(a)
$\begin{aligned} c & =\frac{\mathrm{E}_0}{\mathrm{~B}_0} \text { or } \mathrm{B}_0=\frac{\mathrm{E}_0}{c} \\ \mathrm{~B}_0 & =\frac{9.3}{3 \times 10^8}=3.1 \times 10^{-8} \mathrm{~T}\end{aligned}$
(b) Infrared rays.
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Question 421 Mark
Write names of those radiations of electromagnetic radiations which are :(i) used in satellite communication (ii) used to study crystal structure (iii) produced as a result of decay of radioactive nucleus (iv) wavelength in between 350 nm and 770 nm (v) absorbed by the ozone layer (vi) produce extensive heating effect.
Answer
(i) Micro waves (ii) X-rays (iii) Gamma rays (iv) Visible light (v) Ultraviolet radiation (vi) Infrared radiations,
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Question 431 Mark
Write frequency range of the following electromagnetic radiations and state one use of each :(i) Micro wave (ii) Ultraviolet radiation(iii) Gamma rays.
Answer
(i) $1 \times 10^9 Hz$ to $3 \times 10^{11} Hz$ (In radar)
(ii) $8 \times 10^{14} Hz$ to $1 \times 10^{16} Hz$ (In food conservation)
(iii) $3 \times 10^{18} Hz$ to $3 \times 10^{22} Hz$ (In radio therapy)
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Question 441 Mark
Find wavelength of electromagnetic wave of frequency $4 \times 10^9 Hz$ in vacuum. Write its two uses also.
Answer
$\lambda=\frac{c}{v}=\frac{3 \times 10^8 m / s }{4 \times 10^9 s^{-1}}=0.075 m$ This wavelength is of micro waves and its two uses are :(i) In radar system, (ii) In microwave oven.
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Question 451 Mark
State reason for the generation of displacement current.
Answer
Displacement current is produced due to change in electric field with time and it is written as
$ I_d=\epsilon_0 \frac{d \phi_{E}}{d t} $
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Question 461 Mark
A charged particle oscillates about its mean equilibrium position with a frequency of $10^9 Hz$. What is the frequency of the electromagnetic waves produced by the oscillator?
Answer
We know that an accelerated particle emits electromagnetic waves. A charged particle oscillating with a certain oscillating frequency produces an oscillating electric field which produces oscillating magnetic field. These both oscillating fields produce each other. Frequency of electromagnetic waves is equal to frequency of oscillating charged particle whose magnitude is $10^9 Hz$.
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Question 471 Mark
What physical quantity is the same for X-rays of wavelength $10^{-10} m$, red light of wavelength 6800 Å and radio-waves of wavelength 500 m?
Answer
All three of them are electromagnetic waves. Their speeds will be same in vacuum and it will be equal to the speed of light $c=3 \times 10^8 m / s$.
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