# The Speed of EM Waves

## Trending Questions

**Q.**In a sinusoidal wave, the time required for a particular point to move from maximum displacement to zero displacement is 0.170 second. The frequency of the wave is

- 0.36 Hz
- 1.47 Hz
- 2.94 Hz
- 0.73 Hz

**Q.**In an electromagnetic wave in free space, the root mean square value of the electric field is Erms=6 V/m. The peak value of the magnetic field is

- 4.23×10−8 T
- 1.41×10−8 T
- 2.83×10−8 T
- 0.70×10−8 T

**Q.**An LC circuit contains inductance L=1 μH and capacitance C=0.01 μF. The wavelength of electromagnetic wave generated is nearly

- 0.5 m
- 5 m
- 190 m
- 30 m

**Q.**

An electromagnetic wave travels in a medium with the speed of $2\times {10}^{8}\mathrm{m}/\mathrm{s}$. The relative permeability of the medium is $1$. Find the relative permittivity of the medium.

**Q.**

The oscillating magnetic field in a plane electromagnetic wave is given by: ${B}_{y}=\left(8\times {10}^{-6}\right)\mathrm{sin}\left[2\times {10}^{11}t+300\pi x\right]T$. Calculate the wavelength of the electromagnetic wave.

**Q.**When a ray of light of frequency 6×1014 Hz travels from water of refractive index 43 to glass of refractive index 85, its

- frequency becomes 56th of its initial value.
- speed becomes 56th of its initial value.
- wavelength becomes 65th of its initial value.
- speed becomes 65th of its initial value.

**Q.**

How fast do electromagnetic waves travel in a vacuum?

**Q.**

A plane electromagnetic wave of frequency $500MHz$ is travelling in vacuum along $x,\hspace{0.17em}y,\hspace{0.17em}z$- direction. At a particular point in space and time, $\overrightarrow{B}=8.0\times {10}^{-8}\hat{z}T$ . The value of electric field at this point is: (speed of light$=3\times {10}^{8}m{s}^{\u20131}$) Assume $x,\hspace{0.17em}y,\hspace{0.17em}z$ are unit vectors along $\hat{x},\hat{y}\&\hat{z}$ directions.

$\begin{array}{l}2.6\hat{x}\frac{V}{m}\end{array}$

$\begin{array}{l}-2.6\hat{y}\frac{V}{m}\end{array}$

$\begin{array}{l}24\hat{x}\frac{V}{m}\end{array}$

$\begin{array}{l}-24\hat{x}\frac{V}{m}\end{array}$

**Q.**

How does the speed of electromagnetic wave in vacuum depend upon the source of radiation?

**Q.**In an apparatus, the electric field was found to oscillate with an amplitude of 18 V/m. The magnitude of the oscillating magnetic field will be

- 4 X 10
^{-6 }T - 6 X 10
^{-8 }T - 9 X 10
^{-9 }T - 11 X 10
^{-11 }T

**Q.**An electric dipole of dipole moment p is placed along the x-axis. The angle made by electric field with x-axis at a point P, whose position vector makes an angle theta with x-axis, is: (where, tan alpha=(1/2) tan theta) (A) alpha (B) theta (C) theta + alpha (D) theta + 2*alpha

**Q.**

A string of length L fixed at both ends vibrates in its fundamental mode at a frequency v and a maximum apmplitude A. (a) Find the wavelength and the wave number k. (b) Take the origin at one end of the string and the X-axis along the string. Take the Y-axis along the direction of the displacement. Take t = 0 at the instant when the middle point of the string passes through its mean position and is going towards the positive y-direction. Write the equation describing the standing wave.

**Q.**

If $c$ is the speed of electromagnetic waves in vacuum then $v$, its speed in a medium of dielectric constant $K$ and relative permeability ${\mu}_{r}$ is

$v=\frac{1}{\sqrt{{\mu}_{r}k}}$

$v=c\sqrt{{\mu}_{r}k}$

$v=\frac{c}{\sqrt{{\mu}_{r}k}}$

$v=k\sqrt{{\mu}_{r}c}$

**Q.**Light of wavelength 520 nm passing through a double slit, produces interference pattern of relative intensity versus deflection angle θ as shown in the figure. Find the separation d between the slits.

- 1.98×10−4 m
- 1.98×10−5 m
- 1.98×10−6 m
- 1.98×10−7 m

**Q.**Dimentional formula of permeability of free space μ0 is given by

- [M0LT−2A−2]
- [ML2T−1A−2]
- [MLT−2A−2]
- [M0LT−1A−1]

**Q.**In a region of uniform electric field of magnitude 10 N/C, what will be the energy stored in a sphere of radius 3 m?

- 5×10−8 J
- 9×10−8 J
- 4×10−8 J
- 2×10−8 J

**Q.**A travelling wave represented by y=Asin(ωt−kx) is superimposed on another wave represented by y=Asin(ωt+kx). The resultant is

- A standing wave having nodes atx=(n+12)λ2, where n=0, 1, 2
- /a wavelength travelling along −x direction
- A wave travelling along +x direction
- a standing wave having nodes at x=nλ2, where n=0, 1, 2

**Q.**Which of the given relations is correct {C is speed of light}

- C=1μ0ε0
- EB=C
- E=BC
- EC=B

**Q.**Two point white dots are 1 mm apart on a black paper. They are viewed by eye of pupil diameter 3 mm. Approximately, what is the maximum distance at which dots can be resolved by the eye? [Take wavelength of light = 500 nm]

- 6 m
- 3 m
- 5 m
- 1 m

**Q.**Which of the given relations is correct?

(c is speed of light, E is electric field strength and B is magnetic field strength)

- C=1μ0ε0
- EB=C
- E=BC
- EC=B

**Q.**If the magnetic field in a plane electromagnetic wave is given by →B=3×10−8sin(1.6×103x+48×1010t)^j T then what will be expression for electric field ?

- →E=3×10−8sin(1.6×103x+48×1010t)^i V/m
- →E=3×10−8sin(1.6×103x+48×1010t)^j V/m
- →E=60sin(1.6×103x+48×1010t)^k V/m
- →E=9sin(1.6×103x+48×1010t)^k V/m

**Q.**What are the directions of electric and magnetic field vectors relative to each other and relative to the direction of propagation of electromagnetic waves?

**Q.**An LC circuit contains an inductor and capacitor of L=1 μH & C=0.01 μF. The wavelength of electromagnetic wave generated is nearly

- 0.5 m
- 5 m
- 190 m
- 19 m

**Q.**

The frequency of incident light falling on a photosensitive metal plate is doubled, the kinetic energy of the emitted photoelectrons is

- Unchanged
- Less than doubled
- Double the earlier value
- More than doubled

**Q.**In T.V. broadcasting both picture and sound are transmitted simultaneously because :

- both audio and video signals are frequency modulated
- audio signal is frequency modulated and video signal is amplitude modulated
- both audio and video signals are amplitude modulated
- audio signal is amplitude modulated and video signal is frequency modulated

**Q.**The rms and the average value of the voltage wave shown in the figure are

- √323V;1V
- √113V;1V
- √113V;3V
- √323V;3V

**Q.**A radiation is emitted by 1000 W bulb, and it generates electric field and magnetic field at P, placed at a distance of 2 m. The efficiency of the bulb is 1.25%. The value of peak electric field at P is x×10−1 V/m. Value of x is __________. (Rounded-off to the nearest integer)

[Take ϵo=8.85×10−12 C2/Nm2, c=3×108 m/s]

**Q.**Electrons with energy 80 KeV are incident on the tungsten target of an X-ray tube. K shell electrons of tungsten have −72.5 keV energy. X-rays emitted by the tube contain only :

- A continuous X-ray spectrum (Bremsstrahlung) with a minimum wavelength of −0.155˚A
- A continuous X-ray spectrum (Bremsstrahlung) with all wavelengths
- A continuous X-ray spectrum of tungsten
- A continuous X-ray spectrum (Bremsstrahlung) with a minimum wavelength of −0.155˚A and the characteristic X-ray spectrum of tungsten

**Q.**A monochromatic light of wavelength 589 nm is incident from air onto water surface. The refractive index of water is 1.33. What is the wavelength and speed of refracted light?

- 589nm, 2.256×108ms−1
- 632nm, 3×108ms−1
- 443nm, 2.256×108ms−1
- 726nm, 3×108ms−1

**Q.**The speed of electromagnetic wave in vacuum depends upon the source of radiation. It

- is same for all of them
- decreases as we move from γ-rays to radio waves
- increases as we move from γ-rays to radio waves
- None of these