Question

How many of the following lasers are suitable for showing photoelectric effect with metal A and not with metal B? ($v_0$ of metal $A=4\times {10}^{14}$ Hz, Workfunction of metal $B=3.5eV$)

• A. $4$
• B. $5$
• C. $3$
• D. $2$

Answer 1

The correct option is A $4$

Photoelectric effect will be observed when the energy of the laser will be greater than or equal to the work function. In other words, $\nu \ge {\nu }_o$. This is true for lasers 1 to 6 for metal A and lasers 4 and 5 for metal B. Hence, four lasers are suitable for showing photoelectric effect with metal A and not with metal B.
For metal B, work function $=3.5\times 1.602\times {10}^{-19}=5.607\times {10}^{-19}$
${\nu }_o=\frac{5.607\times {10}^{-19}}{6.626\times {10}^{-34}}=8.5\times {10}^{14}$
For laser 2, $\nu =\frac{c}{\lambda }=\frac{3\times {10}^8}{500\times {10}^{-9}}=6\times {10}^{14}Hz$
For laser 3, $\nu =\frac{c}{\lambda }=\frac{3\times {10}^8}{600\times {10}^{-9}}=5\times {10}^{14}Hz$
For laser 4, $\nu =\frac{c}{\lambda }=\frac{3\times {10}^8}{300\times {10}^{-9}}=1\times {10}^{15}Hz$