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Electromagnetic Waves · Question 29

NEET 2013MCQEasy📈 Topic in 38% papers+4−1
1

The condition under which a microwave oven heats up a food item containing water molecules most efficiently is

  1. Microwaves are heat waves, so always produce heating.
  2. Infra-red waves produce heating in a microwave oven.
  3. The frequency of the microwaves must match the resonant frequency of the water molecules.
  4. The frequency of the microwaves has no relation with natural frequency of water molecules.

Answer

(3) The frequency of the microwaves must match the resonant frequency of the water molecules.

Solution

As per NCERT, in microwave ovens the frequency of the microwaves is selected to match the resonant frequency of water molecules, so that energy from the waves is transferred efficiently to the kinetic energy of the molecules.

This raises the temperature of any food containing water.

Answer: (3)

NEET 2013

Keep practising — Electromagnetic Waves

2

An electromagnetic wave of frequency = 3.0 MHz passes from vacuum into a dielectric medium with relative permittivity r = 4.0. Then

  1. Wavelength is doubled and frequency becomes half.
  2. Wavelength is halved and frequency remains unchanged.
  3. Wavelength and frequency both remain unchanged.
  4. Wavelength is doubled and frequency unchanged.
NEET 2013 (Karnataka)
3

The ratio of amplitude of magnetic field to the amplitude of electric field for an electromagnetic wave propagating in vacuum is equal to

  1. the speed of light in vacuum
  2. reciprocal of speed of light in vacuum
  3. the ratio of magnetic permeability to the electric susceptibility of vacuum
  4. unity
AIPMT 2012 (Mains)
4

The electric field associated with an em wave in vacuum is given by E = i 40 (kz - 6 108 t) where E, z and t are in volt/m, meter and seconds respectively. The value of wave vector k is

  1. 2 m-1
  2. 0.5 m-1
  3. 6 m-1
  4. 3 m-1
AIPMT 2012 (Prelims)
5

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

  1. E = E0 i, B = B0 j
  2. E = E0 k, B = B0 i
  3. E = E0 j, B = B0 i
  4. E = E0 j, B = B0 k
AIPMT 2011 (Prelims)
6

The decreasing order of wavelength of infrared, microwave, ultraviolet and gamma rays is

  1. microwave, infrared, ultraviolet, gamma rays
  2. gamma rays, ultraviolet, infrared, microwaves
  3. microwaves, gamma rays, infrared, ultraviolet
  4. infrared, microwave, ultraviolet, gamma rays
AIPMT 2011 (Prelims)
7

The electric field of an electromagnetic wave in free space is given by E = 10 (107t + kx ) j V/m, where t and x are in seconds and metres respectively. It can be inferred that Which one of the following pairs of statements is correct ?

  1. C and D only
  2. A and B only
  3. B and C only
  4. A and C only
AIPMT 2010 (Mains)
8

Which of the following statements is false for the properties of electromagnetic waves?

  1. Both electric and magnetic field vectors attain the maxima and minima at the same place and same time.
  2. The energy in electromagnetic wave is divided equally between electric and magnetic vectors.
  3. Both electric and magnetic field vectors are parallel to each other and perpendicular to the direction of propagation of wave.
  4. These waves do not require any material medium for propagation.
AIPMT 2010 (Prelims)
9

The electric field part of an electromagnetic wave in a medium is represented by Ex = 0; Ey = 2.5 NC [ (2 106 rads )t - ( 10-2 radm )x ]; Ez = 0. The wave is

  1. moving along x direction with frequency 106 Hz and wavelength 100 m.
  2. moving along x direction with frequency 106 Hz and wavelength 200 m.
  3. moving along -x direction with frequency 106 Hz and wavelength 200 m.
  4. moving along y direction with frequency 2 106 Hz and wavelength 200 m.
AIPMT 2009
10

The velocity of electromagnetic radiation in a medium of permittivity 0 and permeability 0 is given by

  1. 1 0 0
  2. 0 0
  3. 0 0
  4. 0 0
AIPMT 2008
11

The electric and magnetic field of an electromagnetic wave are

  1. in opposite phase and perpendicular to each other
  2. in opposite phase and parallel to each other
  3. in phase and perpendicular to each other
  4. in phase and parallel to each other
AIPMT 2007

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