The work function for metals A, Band C are respectively 1.92

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121.

A leaf which contains only green pigments, is illuminated by a laser light of wavelength 6328 pm. It would appear to be

  • brown

  • black

  • red

  • green


122.

Flash light equipped with a new set of batteries, produces bright white light. As the batteries wear out

  • the light intensity gets reduced with no change in its colour

  • light colour changes first to yellow and then red with no change in intensity

  • it stops working suddenly while giving white light

  • colour changes to red and also intensity gets reduced


123.

If alpha, beta and gamma rays carry same momentum, which has the longest wavelength?

  • Alpha rays

  • Beta rays

  • Gamma rays

  • None all have same wavelength


124.

The kinetic energy of an electron, which is accelerated in the potential difference of 100 V, is

  • 1.6 × 10-17 J

  • 1.6 × 10-14 J

  • 1.6 × 10-10 J

  • 1.6 × 10-8 J


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125.

Light of frequency v falls on material of threshold frequency vo, Maximum kinetic energy of emitted electron is proportional to 

  • ν - νo

  • ν

  • v - vo

  • vo


126.

Which one of the following graph represents the variation of maximum kinetic energy (Ek) of the emitted electrons with frequency v in photoelectric effect correctly?         

                 


127.

A vessel of height 2 d is half filled with a liquid of refractive index 2  and the other half with a liquid of refractive index n (the given liquids are immiscible). Then, the apparent depth of the inner surface of the bottom of the vessel (neglecting the thickness of the bottom of the vessel) will be

  • nd n + 2

  • d n + 2n 2

  • 2 nd n + 2

  • ndd + 2n


128.

Light travels faster in air than that in glass. This is accordance with

  • wave theory of light

  • corpuscular theory of light

  • neigther (a) nor (b)

  • Both (a) and (b)


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129.

The work function for metals A, Band C are respectively 1.92  eV,  2.0 eV and 5 eV. According to Einstein's equation the metals which will emit photo, electrons for a radiation of wavelength 4100 Ao is/are

  • none

  • A only

  • A and B only

  • All the three metals


C.

A and B only

Work function for wavelength of 4100 Ao is

          W = h cλ 

          W = 6.63 × 10-34 × 3 × 1084100 × 10-10

          W = 4.8 × 10-19 J

          W = 4.8 × 10-19 1.6 × 10-19 eV

          W = 3 eV

Now we have,

        WA = 1.22 eV

        WB = 2.0 eV

        WC = 5 eV

Since WA < W and WB < W hence A and B will emit photoelectrons. 

So only metals having a work function less than 3 eV can emit photoelectrons for the incident of wavelength 4100 Ao.


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130.

If the sun rays are incidenting at 60° angle and intensity is I. If the sun rays are made incident at 30° angle, then what will be the intensity?

  • I3

  • 3 l

  • 3 l

  • l3


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