# Electric Field vs Magnetic Field

## Trending Questions

**Q.**

The magnetic potential energy stored in a certain inductor is 25 mJ, when the current in the inductor is 60 mA. The inductor is of inductance

- 0.138 H
- 1.389 H
- 138.88 H
- 13.89 H

**Q.**A) Using the Bohr’s model calculate the speed of the electron in a hydrogen atom in the n = 1, 2, and 3 levels.

B) Using the Bohr’s model calculate the orbital period in the 𝑛 = 1, 2, and 3 levels. (Speed of electron in 𝑛=1, 2 and 3 level is 2.18×106m/s;1.09×106m/s;7.27×105m/s respectively)

=6.6×10−34Js

T3=1(7.27×105)

((3)2(6.6×10−34)22×3.14(9.1×10−31)(9×109)(1.6×10−19)2)

T−3=4.11×10−15s

Final answer : 1.52×10−16s;

1.22×10−15s;4.11×10−15s

**Q.**Ratio of average electric field (E) to average magnetic field (B) is

- speed of light
- speed of oscillating particle
- electric field of EM wave
- magnetic field of EM wave

**Q.**

To find the distance $d$ over which a signal can be seen clearly in foggy conditions, a railway engineer uses dimensional analysis and assumes that the distance depends on the mass density $\rho $ of the fog, the intensity $\left(\frac{power}{area}\right)S$ of the light from the signal, and its frequency $f$. The engineer finds that $d$ is proportional to ${S}^{\frac{1}{n}}$. The value of $n$

$2$

$3$

$1$

$4$

**Q.**

A beam of plane polarized light of large cross-sectional area and uniform intensity of $3.3{\mathrm{Wm}}^{-2}$falls normally on a polarizer (cross sectional area $3\times {10}^{-4}{\mathrm{m}}^{2}$) which rotates about its axis with an angular speed of $31.4\mathrm{rad}/\mathrm{s}$. The energy of light passing through the polarizer per revolution is close to:

$1.0\times {10}^{-4}\mathrm{J}$

$1.0\times {10}^{-5}\mathrm{J}$

$5.0\times {10}^{-4}\mathrm{J}$

$1.5\times {10}^{-4}\mathrm{J}$

**Q.**

The electric field of a plane electromagnetic wave propagating along the x-direction in a vacuum is $\overrightarrow{E}={E}_{\circ}\hat{j}\mathrm{cos}\left(\omega t-kx\right)$.The magnetic field $\overrightarrow{B}$ at the moment $t=0$ is:

$\overrightarrow{B}=\frac{{E}_{\circ}}{\sqrt{{\mu}_{\circ}{\epsilon}_{\circ}}}\mathrm{cos}\left(kx\right)\hat{j}$

$\overrightarrow{B}=\frac{{E}_{\circ}}{\sqrt{{\mu}_{\circ}{\epsilon}_{\circ}}}\mathrm{cos}\left(kx\right)\hat{k}$

$\overrightarrow{B}={E}_{\circ}\sqrt{{\mu}_{\circ}{\epsilon}_{\circ}}\mathrm{cos}\left(kx\right)\hat{j}$

$\overrightarrow{B}={E}_{\circ}\sqrt{{\mu}_{\circ}{\epsilon}_{\circ}}\mathrm{cos}\left(kx\right)\hat{k}$

**Q.**An electron (mass = 9.1×10−31 kg charge =−1.6×10−19 C) experiences no deflection if subjected to an electric field of 3.2×105 V/m and a magnetic field of 2.0×10−3 Wb/m2. Both the fields are normal to the path of electron and to each other. If the electric field is removed, then the electron will revolve in an orbit of radius

- 45 m

- 4.5 m
- 0.45 m
- 0.045 m

**Q.**

If →E and →B are the electric and magnetic field vectors of E.M. waves then the direction of propagation of E.M. wave is along the direction of

→E

→B

→E× →B

None of these

**Q.**The electric and the magnetic field, associated with an EM wave, propagating along the +z-axis, can be represented by

- →E=E0ˆj, →B=B0ˆk
- →E=E0ˆi, →B=B0ˆj
- →E=E0ˆk, →B=B∘ˆi
- →E=E0ˆj, →B=B0ˆi

**Q.**A light beam travelling in the X-direction is described by the electric field Ey=(300 V/m)sin ω(t−x/c). An electron is constrained to move along the Y-direction with a speed of 2.0×107 m/s. Find the maximum electric force and the maximum magnetic force on the electron respectively.

- 3.6×10−17 N, 2.5×10−18 N
- 4.8×10−17 N, 3.2×10−18 N
- 9.6×10−17 N, 6.4×10−18 N
- 2.4×10−17 N, 1.6×10−18 N

**Q.**A proton has spin and magnetic moment just like an electron. Why then its effect is neglected in magnetism of materials?

**Q.**

1) In 1959 Lyttleton and Bondi suggested that the expansion of the Universe could be explained if matter carried a net charge. Suppose that the Universe is made up of hydrogen atoms with a number density N, which is maintained a constant. Let the charge on the proton be:

ep=–(1+y)e

where e is the electronic charge.

A) Find the critical value of y such that expansion may start.2) In 1959 Lyttleton and Bondi suggested that the expansion of the Universe could be explained if matter carried a net charge. Suppose that the Universe is made up of hydrogen atoms with a number density N, which is maintained a constant. Let the charge on the proton be:

ep=–(1+y)e

where e is the electronic charge.

B) Show that the velocity of expansion is proportional to the distance from the centre.**Q.**A light beam travelling in the x-direction is described by the electric field Ey=300 Vm−1 sin ω(t−xc). An electron is constrained to move along the y-direction with a speed of 2.0×107 ms−1. Find the maximum electric force and the maximum magnetic force on the electron.

- FE=4.8×10−17N and FB=3.2×10−18N
- FE=8.4×10−18N and FB=3.2×10−18N
- FE=3.2×10−17N and FB=4.8×10−18N
- FE=4.8×10−17N and FB=6.4×10−17N

**Q.**A bar magnet of magnetic moment 2 Am2 is free to rotate about a vertical axis passing through its centre. The magnet is then released from rest at east -west position. Find the Kinetic energy of the magnet as it takes north-south position is

**Q.**Amplitude of electric field in a laser beam of power 4.4 mW with cross-sectional area of 2 mm2 is

- 2 kV/m
- 232 kV/m
- √23 kV/m
- √53 kV/m

**Q.**

The intensity of the sunlight reaching the earth is 1.380Wm−2 Assume this light to be a plane, monochromatic wave. Find the amplitudes of electric and magnetic fields in this wave

**Q.**The approximate operating magnetic field for accelerating protons in a cyclotron oscillator having frequency of 12 MHz is:

- 0.790 T
- 0.690 T
- 0.395 T
- 0.345 T

**Q.**A proton beam passes without deviation through the region of space where there exists uniform transverse mutually perpendicular electric and magnetic field with E=120 kV/m and B=50 mT. The beam strikes a ground target. Find the force imparted by the beam on the target if the beam current is equal to 0.80 mA.

- 15.4 μN
- 19.2 μN
- 28.2 μN
- 45 μN

**Q.**A non-relativistic proton beam passes without deviation through the region of space where uniform transverse mutually perpendicular electric and magnetic fields of E=120 kVm−1 and B=50 mT. Then the beam strikes a grounded target. Find the force with which the beam hits on the target if the beam current is equal to I=0.80 mA.[Take mass of proton and its charge as me=1.67×10−27 kg and q=1.6×10−19 C respectively.]

- 10 μN
- 40 μN
- 30 μN
- 20 μN

**Q.**

A laser beam has intensity 2.5×1014 W m−2 Find the amplitudes of electric and magnetic fields in the beam.

**Q.**Maximum value of electric field at a point at a distance of 2 m from the light source of power 60 watt is

- 50N/C
- 30N/C
- 2×10−3N/C
- 5×10−3N/C

**Q.**At the threshold of detection, an FM receiver can pick up a signal for which E0=2 μV/m. The intensity of the electromagnetic wave is -

- 5.31×10−15 W-m−2
- 5.31×10−12 W-m−2
- 5.31×10−14 W-m−2
- 5.31×10−17 W-m−2

**Q.**Write the relation for the speed of electromagnetic waves and the amplitudes of electric and magnetic fields.

**Q.**(a) Give three reasons why modulation of a message signal is necessary for long distance transmission.

(b) Show graphically an audio signal, a carrier wave and an amplitude modulated wave

**Q.**The electric field associated with a light wave is given by E=E0sin[(1.57×107)(x−ct)](where, x and t are in metre and second). The stopping potential when its light is used in an experiment on photoelectric effect with the emitter having work function ϕ=19eV is?

- 1.8eV
- 0.6eV
- 2.4eV
- 1.2eV

**Q.**The sunlight reaching the earth has maximum electric field of 810 V/m. What is the maximum magnetic field in this light?

- 2.7 μT
- 1.8 μT
- 0.9 μT
- 0.3 μT

**Q.**The short-wavelength limit shifts by 26 pm when the operating voltage in an X-ray tube is increased to 1.5 times the original value. What was the original value of the operating voltage?

- 25.56 kV
- 36.78 kV
- 15.93 kV
- 8.12 kV

**Q.**A light beam travelling in the x− direction is described by the electric field Ey=(300 Vm−1)sinω(t−x/c). An electron is constrained to move along the y−direction with a speed of 2.0×107 ms−1. If the maximum electric force acting on the electron is FE and the maximum magnetic force acting on the electron is FB, then

- FE=1.60×10−17 N
- FE=4.8×10−17 N
- FB=1.6×10−18 N
- FE>FB

**Q.**In a plane electromagnetic wave, the electric field of amplitude 1Vm−1 varies with time in free space. The average energy density of magnetic field is (in Jm−2)

- 8.86×10−12
- 17.72×10−12
- 4.43×10−12
- 1.11×10−12
- 2.21×10−12

**Q.**In a wave E0=100Vm−1. Find the Poynting vector magnitude.

- 13.25Wm−2
- 26.5Wm−2
- 18.25Wm−2
- 19.7Wm−2