The threshold frequency for a metallic surface corresponds to an energy of 6.2 eV, and the stopping potential for a radiation incident on this surface 5 V. The incident radiation lies in

  • X-ray region

  • ultra-violet region

  • infra-red region

  • infra-red region


B.

ultra-violet region

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The direction of propagation of electromagnetic wave is along

  • Electric field vector, E

  • Magnetic field vector, B

  • E . B

  • E × B


D.

E × B

The direction of propagation of electromagnetic wave is always perpendicular to the plane in which E and B lies and,

         E × B = C


During the propagation of electromagnetic waves in a medium:

  • Electric energy density is equal to the magnetic energy density.

  • Both electric and magnetic energy densities are zero.

  • Electric energy density is double of the magnetic energy density.

  • Electric energy density is double of the magnetic energy density.


C.

Electric energy density is double of the magnetic energy density.

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Assume that a radio station is about 200 km away at your location and the station operates 972 kHz. How long does it take for an electromagnetic signal to travel from the station to you and how many wave crests does it send out per second ?

  • 666 µs and 9.72 × 105 crests per second

  • 666 µs and 972 × 105 crests per second

  • 555 µs and 97.2 × 107 crests per second

  • 555 µs and 0.972 × 105 crests per second


A.

666 µs and 9.72 × 105 crests per second

The speed of radio waves is equal to electromagnetic wave speed i.e. 3 x 108 m/s

Given, the distance of radio station, s = 200 km

            = 200 × 103 m

Time taken by radio wave to his toner

      t = sc = 200 × 1033 × 108  = 666 × 10-6  = 666 μs

The wave emitted send out per second = 972 kHz

        = 972 × 103 Hz

        = 9.72 × 105 crest per second


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An electromagnetic wave in vaccum has the electric and magnetic fields straight E with rightwards arrow on top and straight B with rightwards arrow on topwhich are always perpendicular to each other. the direction of polarisation is given by straight x with rightwards arrow on top and that of wave propagation by straight k with rightwards arrow on top then

  • straight X with rightwards arrow on top vertical line vertical line straight B with rightwards arrow on top space and space straight X with rightwards arrow on top vertical line vertical line straight B with rightwards arrow on top space straight x space straight E with rightwards arrow on top
  • straight X with rightwards arrow on top vertical line vertical line straight E with rightwards arrow on top space and straight k with rightwards arrow on top vertical line vertical line space straight E with rightwards arrow on top straight x straight B with rightwards arrow on top
  • straight X with rightwards arrow on top vertical line vertical line straight B with rightwards arrow on top space and space straight k with rightwards arrow on top vertical line vertical line straight E with rightwards arrow on top space straight x straight B with rightwards arrow on top
  • straight X with rightwards arrow on top vertical line vertical line straight B with rightwards arrow on top space and space straight k with rightwards arrow on top vertical line vertical line straight E with rightwards arrow on top space straight x straight B with rightwards arrow on top


C.

straight X with rightwards arrow on top vertical line vertical line straight B with rightwards arrow on top space and space straight k with rightwards arrow on top vertical line vertical line straight E with rightwards arrow on top space straight x straight B with rightwards arrow on top
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