Chapter 15

The dimensional formula of \(\mu_{0} \mathrm{E}_{0}\) is (A) \(L^{2} T^{-2}\) (B) \(L^{-2} T^{2}\) (C) \(\mathrm{L}^{1} \mathrm{~T}^{-1}\) (D) \({L}^{-1} \mathrm{~T}^{1}\)

A plane electromagnetic wave is incident on a mater1al surface. The wave delivers momentum \(P\) and energy \(E\) (A) \(\mathrm{P}=0, \mathrm{E} \neq 0\) (B) \(\mathrm{P} \neq 0, \mathrm{E}=0\) (C) \(P \neq 0, E \neq 0\) (D) \(P=0, E=0\)

If \(\mathrm{V}_{\mathrm{r}}, \mathrm{V}_{\mathrm{x}}\) and \(\mathrm{V}_{\mathrm{m}}\) are the velocity of the \(\gamma\) rays, \(\mathrm{x}\) rays, micro waves respectively in space, then (A) \(\mathrm{V}_{\gamma}<\mathrm{V}_{\mathrm{x}}<\mathrm{V}_{\mathrm{m}}\) (B) \(\mathrm{V}_{\mathrm{r}}=\mathrm{V}_{\mathrm{x}}=\mathrm{V}_{\mathrm{m}}\) (C) \(\mathrm{V}_{\mathrm{r}}^{\prime}>\mathrm{V}_{\mathrm{x}}>\mathrm{V}_{\mathrm{m}}\) (D) \(\mathrm{V}_{\mathrm{r}}>\mathrm{V}_{\mathrm{x}}<\mathrm{V}_{\mathrm{m}}\)

If \(\lambda_{\gamma} \lambda_{\mathrm{x}}\) and \(\lambda_{\mathrm{m}}\) are the wave lengths of the \(\gamma\) -rays, \(\mathrm{x}\) rays and micro waves respectively in space then (A) \(\lambda_{\gamma}>\lambda_{\mathrm{x}}>\lambda_{\mathrm{m}}\) (B) \(\lambda_{\gamma}<\lambda_{\mathrm{x}}<\lambda_{\mathrm{m}}\) (C) \(\lambda_{r}=\lambda_{x}=\lambda_{m}\) (D) \(\lambda_{\gamma}<\lambda_{\mathrm{m}}<\lambda_{\mathrm{x}}\)

According to Maxwell, a changing electric field produces (A) emf (B) Electric current (C) magnetic field (D) radiation pressure

An electromagnetic wave going through vacuum is described by \(E=E_{0} \sin (k x-\cot )\). Which of the following is independent of the wavelength? (A) \(\omega\) (B) \((\mathrm{k} / \mathrm{c})\) (C) \(\mathrm{k}_{\mathfrak{e}}\) (D) \(\mathrm{k}\)

Which of the following have zero average value in a plane electromagnetic wave? (A) Electric energy (B) Magnetic energy (C) Electric field (D) None of these.

If the relative permeability and dielectric constant of a given medium are equal to \(\mu_{\mathrm{r}}\) and \(\mathrm{K}\) respectively, then the refractive index of the medium is equal to (A) \(\sqrt{\left(\mu_{\mathrm{T}} \mathrm{K}\right)}\) (B) \(\sqrt{\left(\mu_{1} E_{0}\right)}\)

Astronomers have found that electromagnetic waves of wavelength \(21 \mathrm{~cm}\) are continuously reaching the Earth's surface. Calculate the frequency of this radiation. \(\left(\mathrm{c}=3 \times 10^{8} \mathrm{~m} / \mathrm{s}\right)\) (A) \(14.28 \mathrm{GHz}\) (B) \(1.428 \mathrm{kHz}\) (C) \(1.428 \mathrm{MHz}\) (D) \(1.428 \mathrm{GHz}\)

Speed of electromagnetic wave is the same (A) for all wavelengths (B) in all media (C) for all intensities (D) for all frequencies

The maximum electric field in a plane electromagnetic wave is \(900 \mathrm{NC}^{-1}\). The wave is going in the \(\mathrm{x}\) direction and the electric field is in the y direction. The maximum magnetic field in the wave is \(\mathrm{T}\) (A) \(3 \times 10^{-8}\) (B) \(3 \overline{\times 10^{-6}}\) (C) \(27 \times 10^{-6}\) (D) \(27 \times 10^{10}\)

Electromagnetic waves are produced by (A) a static charge (B) a moving charge (C) an accelerating charge (D) chargeless particles

Maxwells equations are derived from the laws of (A) electricity (B) magnetism (C) both electricity and magnetism (D) mechanics

Which of the following electromagnetic waves has the longest wavelength? (A) Radio waves (B) Infrared radiations (C) x rays (D) visible rays

Which of the following electromagnetic waves has the highest frequency? (A) radiowaves (B) microwaves (C) \(\gamma\) rays (D) \(\mathrm{x}\) rays

Which of the following electromagnetic waves is used in telecommunication? (A) radiowaves (B) visible radiations (C) ultraviolet rays (D) microwaves

The maximum value of \(\mathrm{E}^{-}\) in an electromagnetic waves in air is equal to \(6.0 \times 10^{-4} \mathrm{Vm}^{-1}\). The maximum value of \(\mathrm{B}^{-}\) is (A) \(1.8 \times 10^{5} \mathrm{~T}\) (B) \(2.0 \times 10^{4} \mathrm{~T}\) (C) \(2.0 \times 10^{-12} \mathrm{~T}\) (D) \(1.8 \times 10^{13} \mathrm{~T}\)

Dimensional formula of intensity of radiation is (A) \(\mathrm{M}^{1} \mathrm{~L}^{2} \mathrm{~T}^{-2}\) (B) \(\mathrm{M}^{1} \mathrm{~L}^{0} \mathrm{~T}^{-2}\) (C) \(\mathrm{M}^{1} \mathrm{~L}^{2} \mathrm{~T}^{-3}\) (D) \(\overline{\mathrm{M}^{1} \mathrm{~L}^{0} \mathrm{~T}^{-3}}\)

The frequency of an electromagnetic wave in free space 15 \(3 \mathrm{MHz}\). When it passes through a medium of relative permeability \(\varepsilon_{\mathrm{r}}=4.0\), then its frequency (A) becomes half (B) become doubled (C) remain same (D) become \(\sqrt{2}\) times

The frequency of electromagnetic wave having wavelength \(25 \mathrm{~mm}\) is \(\quad \mathrm{Hz}\) (A) \(1.2 \times \overline{10^{10}}\) (B) \(7.5 \times 10^{5}\) (C) \(1.2 \times 10^{8}\) (D) \(7.5 \times 10^{6}\)

Unit of energy density of electromagnetic wave is (A) \(\mathrm{Jm}^{-3}\) (B) \(\mathrm{Jm}^{-2}\) (C) \(\mathrm{wm}^{-2}\) (D) None of these

What is the ratio of velocities of light rays of wavelengths \(4000^{\circ} \mathrm{A}\) and \(8000^{\circ} \mathrm{A}\) in vacuum? (A) \(1: 2\) (B) \(1: 1\) (C) \(2: 1\) (D) cannot be determined

Which of the following rays are not electromagnetic waves? (A) \(\alpha\) rays (B) \(\gamma\) rays (C) \(\beta\) rays (D) heat rays

A new system of unit is evolved in which the values of \(\mu_{0}\) and \(\varepsilon_{0}\) are 2 and 8 respectively. Then the speed of light in this system will be (A) \(0.25\) (B) \(0.5\) (C) \(0.75\) (D) 1

Our eyes respond to wavelength ranging from (A) \(400 \mathrm{~nm}\) to \(700 \mathrm{~nm}\) (B) \(-\infty\) to \(+\infty\) (C) \(1 \mathrm{~mm}\) to \(700 \mathrm{~nm}\) (D) \(700 \mathrm{~nm}\) to \(800 \mathrm{~nm}\)

In microwave oven, we use electromagnetic oscillators which produce electromagnetic waves in the wavelength range (A) \(1 \mathrm{~mm}\) to \(10 \mathrm{~m}\) (B) \(0.7 \mu \mathrm{m}\) to \(1 \mathrm{~mm}\) (C) \(0.1 \mathrm{~m}\) to \(1 \mathrm{~mm}\) (D) \(0.1 \mu \mathrm{m}\) to \(0.7 \mu \mathrm{m}\)

What is the direction of \(\mathrm{E}^{-} \times \mathrm{B}^{-}\) in an electromagnetic wave? (A) same as that of \(E^{-}\) (B) same as that of \(\mathrm{B}^{-}\) (C) same as the direction of propagation of electromagnetic wave (D) none of these

The wavelength of \(\mathrm{x}\) rays is of the order of (A) \(1 \mathrm{~cm}\) (B) \(1 \mathrm{~m}\) (C) Imicron (D) 1angstrom

A plane electromagnetic wave of frequency \(25 \mathrm{MHz}\) travels in free space along the \(\mathrm{x}\) direction. At a particular point in space and time \(\mathrm{E}^{-}=6.3 \mathrm{j} \wedge \mathrm{Vm}^{-1}\) then \(\mathrm{B}^{-}\) at this point is (A) \(2.1 \times 10^{-8}\) i \(\mathrm{T}\) (B) \(2.1 \times 10^{-8} \mathrm{k} \wedge \mathrm{T}\) (C) \(1.89 \times 10^{9} \mathrm{k} \wedge \mathrm{T}\) (D) \(2.52 \times 10^{-7} \mathrm{k} \wedge \mathrm{T}\)

A plane electromagnetic wave of frequency \(25 \mathrm{MHz}\) travels in free space along the \(\mathrm{x}\) direction. At a particular point in space and time \(\mathrm{E}^{-}=6.3 \mathrm{j} \wedge \mathrm{Vm}^{-1}\) then \(\mathrm{B}^{-}\) at this point is (A) \(2.1 \times 10^{-8}\) i \(\mathrm{T}\) (B) \(2.1 \times 10^{-8} \mathrm{k} \wedge \mathrm{T}\) (C) \(1.89 \times 10^{9} \mathrm{k} \wedge \mathrm{T}\) (D) \(2.52 \times 10^{-7} \mathrm{k} \wedge \mathrm{T}\)

Light with an energy flux of \(18 \mathrm{w} / \mathrm{m}^{2}\) or \(\mathrm{Wm}^{-2}\) falls on a non-reflecting surface at normal to surface. If the surface has an area of \(20 \mathrm{~m}^{2}\). The average force exerted on the surface during 30 minutes is (A) \(6.48 \times 10^{5} \mathrm{~N}\) (B) \(3.60 \times 10^{2} \mathrm{~N}\) (C) \(1.2 \times 10^{-6} \mathrm{~N}\) (D) \(2.16 \times 10^{-3} \mathrm{~N}\)

Energy density of an electromagnetic wave of intensity \(0.02 \mathrm{Wm}^{-2}\) is (A) \(6.67 \times 10^{-11} \mathrm{Jm}^{-3}\) (B) \(6 \times 10^{6} \mathrm{Jm}^{-3}\) (C) \(1.5 \times 10^{10} \mathrm{Jm}^{-3}\) (D) none of the above

The waves used in communication are generally called (A) \(\gamma\) rays (B) \(\alpha\) rays (C) microwaves (D) radiowaves

For an electromagnetic wave, the phase difference between vectors \(\mathrm{E}^{-}\) and \(\mathrm{B}^{-}\) (far away from the source) (A) 0 (B) \([\pi / 2]\) (C) \(\pi\) (D) \([3 \pi / 2]\)

In an electromagnetic wave, if the amplitude of magnetic field is \(3 \times 10^{-10} \mathrm{~T}\), the amplitude of the associated electric field will be (A) \(9 \times 10^{-2} \overline{\mathrm{Vm}^{-1}}\) (B) \(3 \times 10^{-10} \mathrm{Vm}^{-1}\) (C) \(3 \times 10^{-2} \mathrm{Vm}^{-1}\) (D) \(1 \times 10^{-18} \mathrm{Vm}^{-1}\)

The electric and magnetic field of an electromagnetic wave are (A) in phase and perpendicular to each other (B) in phase and parallel to each other (C) in opposite phase and perpendicular to each other (D) in opposite phase and parallel to each other

The frequency of light wave of wavelength \(5000 \mathrm{~A}\) is \(\mathrm{Hz}\) (A) \(6 \times 10^{14}\) (B) \(1.5 \times 10^{-2}\) (C) \(1.5\) (D) \(6 \times 10^{1}\)

Unit of \(\mu_{0} \mathrm{C}\) is same as that of (A) current (B) resistance (C) electric charge (D) velocity

The amplitude of the magnetic field part of an electromagnetic wave in vacuum is \(\mathrm{Bm}=510 \mathrm{nT}\). Then the amplitude of the electric part of the wave is (A) \(1.53 \times 10^{11} \mathrm{~V} / \mathrm{m}\) (B) \(1.53 \mathrm{~V} / \mathrm{m}\) (C) \(1.53 \times 10^{2} \mathrm{~V} / \mathrm{m}\) (D) \(1.53 \times 10^{8} \mathrm{~V} / \mathrm{m}\)

If the direction of magnetic field \(\mathrm{B}^{\rightarrow}\) at some instant is along + ve \(Z\) direction and the electromagnetic wave is propagating along + ve \(\mathrm{X}\) direction, then the direction of electric field \(\mathrm{E}^{\rightarrow}\) at that instant is (A) along - ve Y direction (B) along + ve Y direction (C) along + ve \(\mathrm{X}\) direction (B) along - ve \(\mathrm{X}\) direction

Relation between amplitudes of electric and Magnetic field is (A) \(E_{0}=B_{0}\) (B) \(E_{0}=\mathrm{cB}_{0}\) (C) \(E_{0}=\left(B_{0} / c\right)\) (D) \(E_{0}=\left(\mathrm{c} / \mathrm{B}_{0}\right)\)

The velocity of light in vacuum can be changed by changing (A) frequency (B) wavelength (C) amplitude (D) none of these

An electromagnetic wave going through vacuum is described by \(E=E_{0} \sin (k x-\omega t)\) then \(B=B_{0} \sin (k x-\omega t)\) then (A) \(E_{0} B_{0}=\operatorname{cok}\) (B) \(E_{0} k=B_{0} \omega\) (C) \(\mathrm{E}_{0} \mathrm{~m}=\mathrm{B}_{0} \mathrm{k}\) (D) none of these

If the wavelength of light is \(4000^{\circ} \mathrm{A}\) then the number of waves in \(1 \mathrm{~mm}\) length will be (A) \(2.5\) (B) 2500 (C) 250 (D) 25000

The SI unit of displacement current is (A) coulomb (B) henry (C) ampere (D) faraday

The electromagnetic waves do not transport (A) energy (B) charge (C) momentum (D) information

An electric charge oscillating with a frequency of 1 kilo cycles/s can radiates electromagnetic waves of wavelength (A) \(100 \mathrm{~km}\) (B) \(200 \mathrm{~km}\) (C) \(300 \mathrm{~km}\) (D) \(400 \mathrm{~km}\)

The frequency \(1057 \mathrm{MHz}\) of radiation arising from two close energy levels in hydrogen belongs to (A) radio waves (B) infrared waves (C) micro waves (D) \gamma rays

Electromagnetic waves travelling in a medium which has relative permeability \(1.3\) and relative permittivity \(2.14\) speed of electromagnetic waves in this medium will be (A) \(3.6 \times 10^{8} \mathrm{~m} / \mathrm{s}\) (B) \(1.8 \times 10^{8} \mathrm{~m} / \mathrm{s}\) (C) \(1.8 \times 10^{6} \mathrm{~m} / \mathrm{s}\) (D) \(13.6 \times 10^{6} \mathrm{~m} / \mathrm{s}\)

A plane electromagnetic wave is incident on a material surface. If the wave delivers momentum \(p\) and energy \(E\), then (A) \(p=0, E=0\) (B) \(p \neq 0, E \neq 0\) (C) \(p \neq 0, E=0\) (D) \(p=0, E \neq 0\)