Question

heyy guys plz help...
i didn't understand that how 12400 came... can anyone plz explain this process ☹️​

Answer 1

Given :

• work function = 2 e V
• wavelength = 4000 A °

Solution:

we know that ,

$\implies{E = \frac{hc}{ \lambda}}$

here ,

$\implies{h = 6.63 \times {10}^{ - 34} \frac{J}{s} }$

to convert it into eV / s ,

$\implies{h = \frac{6.6 \times {10}^{ - 34} }{1.6 \times {10}^{ - 19} } }$

$\implies{h = 4.14 \times {10}^{ - 15} \frac{eV}{m} }$

Now multiplying h by c we get ,

$\implies{hc = 4.14 \times {10}^{ - 15} \times 3 \times {10}^{8} }$

$\implies{hc = 12.42 \times {10}^{ - 7} }$

$\boxed{hc = 12420 \times {10}^{ - 10} }$

Substituting the value of hc in E we get

$\implies{E = \frac{12400 \times {10}^{ - 10} }{ 4000 \times {10}^{ - 10} } }$

$\boxed{E =3.1eV}$

we know that ,

$\implies{KE = E - W}$

$\implies{KE = 3.1 - 2}$

$\implies{KE = 1.1 e V}$

$\implies{KE = 1.1 \times 1.6 \times {10}^{ - 19} J}$

$\boxed{KE = 1.76 \times {10}^{ - 19} J}$