JEE PYQ: Atomic Structure Question 1
Question 1 - 2021 (16 Mar Shift 1)
When light of wavelength 248 nm falls on a metal of threshold energy 3.0 eV, the de-Broglie wavelength of emitted electrons is ____ $\AA$.
(Round off to the Nearest Integer).
[Use: $\sqrt{3} = 1.73$, $h = 6.63 \times 10^{-34}$ J s, $m_e = 9.1 \times 10^{-31}$ kg, $c = 3.0 \times 10^{8}$ m s$^{-1}$, $1$ eV $= 1.6 \times 10^{-19}$ J]
Show Answer
Answer: 9
Solution
Energy $= \frac{hc}{\lambda} = 5$ eV. $KE = 5 - 3 = 2$ eV $= 3.2 \times 10^{-19}$ J. $\lambda = \frac{h}{\sqrt{2 \cdot KE \cdot m}} = 8.72 \times 10^{-10}$ m $\approx 9$ $\AA$.
BETA
