8. Electro Magnetic Waves

Which of the following has/have zero average value in a plane electromagnetic wave?

• Both Magnetic and Electric Fields

• Electric Field only

• Magnetic Field only

• None of these

The amplitude of the magnetic field of a harmonic electromagnetic wave in vacuum is B₀ = 510 nT. The amplitude of the electric field part of the wave is

• 120 NC^-1

• 134 NC^-1

• 510 NC^-1

• 153 NC^-1

Radiations of intensity 0.5 W m^–2 are striking a metal plate. The pressure on the plate is

• 0.166 X 10^-8 N m^-2

• 0.332 X 10^-8 N m^-2

• 0.111 X 10^-8 N m^-2

• 0.083 X 10^-8 N m^-2

Molybdenum is used as a target element for the production of X-rays because it is

• light and can easily deflect electrons

• light and can absorb electrons

• a heavy element with a high melting point

• an element having high thermal conductivity

• moving along the x direction with frequency 10⁶ Hz and wavelength 100 m

• moving along x direction with frequency 10⁶ Hz and wavelength 200 m

• moving along –x direction with frequency 10⁶ Hz and wavelength 200 m

• moving along y direction with frequency 2pi × 10⁶ Hz and wavelength 200 m.

The amplitude of magnetic field in a parallel beam of light of intensity 2.0 W m^–2 is

• 1.3 x 10^-7 T

• 1.3 x 10^-6 T

• 1.3 x 10^-5 T

• 1.3 x 10^-8 T

Light with an energy flux of 18 W cm^–2 falls on a non-reflecting surface at normal incidence. If the surface has an area of 20 cm², the total momentum delivered to the surface during a span of 30 minutes is

• 2.16 x 10^-3 kg ms^-1

• 2.16 x 10^-4 kg ms^-1

• 4.32 x 10^-3 kg ms^-1

• 4.32 x 10^-4 kg ms^-1

An earth orbiting satellite has solar energy collecting panel with total area 5 m². If solar radiations are perpendicular and completely absorbed, the average force associated with the radiation pressure is (solar constant = 1.4 kW m^–2).

• 2.33 x 10^-3 N

• 2.33 x 10^-4 N

• 2.33 x 10^-5 N

• 2.33 x 10^-6 N