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NCERT Class XII Chapter
Dual Nature of Radiation and Matter
Questions With Solutions

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Question : 10
Total: 37
Light of frequency 7.21 × 1014 Hz is incident on a metal surface. Electrons with a maximum speed of 6.0 × 105ms–1 are ejected from the surface. What is the threshold frequency for photoemission of electrons?
Solution:  
According to Einstein’s equation
hv = hv0+
1
2
mvmax2
So, threshold frequency
v0 =
hv−
1
2
mvmax2
h
 or v0 = v -
mvmax2
2h
v0 = 7.21 × 1014 -
9.1×10−31×(6×105)2
2×(6.63×10−34)
v0 = 4.74 × 1014 Hz
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