Dual Nature of Radiation and Matter - Result Question 50
52. The work functions for metals $A, B$ and $C$ are respectively $1.92 eV, 2.0 eV$ and $5 eV$. According to Einstein’s equation, the metals which will emit photoelectrons for a radiation of wavelength $4100 \AA$ is/are
[2005]
(a) none
(b) A only
(c) A and B only
(d) all three metals
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Answer:
Correct Answer: 52. (c)
Solution:
(c) $E=\frac{h c}{\lambda}$ $\Rightarrow E=\frac{12375}{\lambda(\text{ in } A)} eV \Rightarrow E=\frac{12375}{4100} eV$
$\Rightarrow E \approx 3 eV$
So, only metals having work function less than $3 eV$ can emit photoelectrons for the incident radiation of wavelength $4100 \AA$.
(a) K.E. $=h v-\phi$
$\therefore$ graph of K.E. versus $v$ is a straight line with $+v e$ slope $h$ and K.E. $>0$ for $v$ such that $h v>\phi$.
