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Question: Light of frequency \(7.21 \times 10 ^ { 14 } \mathrm {~Hz}\)is incident on a metal surface. Electron...

Light of frequency 7.21×1014 Hz7.21 \times 10 ^ { 14 } \mathrm {~Hz}is incident on a metal surface. Electrons with a maximum speed of 6×105 ms−16 \times 10 ^ { 5 } \mathrm {~ms} ^ { - 1 } are ejected from the surface. The threshold frequency fro photoemission of electrons is : (Given h= 6.63×10-34Js, ):

A

2.32×1014 Hz2.32 \times 10 ^ { 14 } \mathrm {~Hz}

B

2.32×1012 Hz2.32 \times 10 ^ { 12 } \mathrm {~Hz}

C

4.74×1014 Hz4.74 \times 10 ^ { 14 } \mathrm {~Hz}

D

4.74×1012 Hz4.74 \times 10 ^ { 12 } \mathrm {~Hz}

Answer

4.74×1014 Hz4.74 \times 10 ^ { 14 } \mathrm {~Hz}

Explanation

Solution

: Here

According to Einstein’s photoelectric equation

=7.21×1014−(9.1×10−31)×(6×105)22×6.63×10−34= 7.21 \times 10 ^ { 14 } - \frac { \left( 9.1 \times 10 ^ { - 31 } \right) \times \left( 6 \times 10 ^ { 5 } \right) ^ { 2 } } { 2 \times 6.63 \times 10 ^ { - 34 } } =7.21×1014−2.47×1014= 7.21 \times 10 ^ { 14 } - 2.47 \times 10 ^ { 14 } =4.74×1014 Hz= 4.74 \times 10 ^ { 14 } \mathrm {~Hz}