Jee Main 2024 31 01 2024 Shift 1 - Question15
Question 15
When light of wavelength $\lambda$ is incident on a metal, the stopping potential is $8 V$. If the wavelength is made $3 \lambda$ the stopping potential becomes $2 V$. Find the threshold wavelength for the photoelectric effect.
(1) $2.6 \times 10^{-6} m$
(2) $2.8 \times 10^{-7} m$
(3) $1.24 \times 10^{-6} m$
(4) $1.24 \times 10^{-7} m$
Show Answer
Answer: (3)
Solution:
$(8 e)=\frac{h c}{\lambda}-\phi _0$
(2e) $\frac{h c}{3 \lambda}-\phi _0$
$\phi _0=1 eV$
$\therefore \quad \lambda _{\text {th }}=12400 \mathring{A}$
$\lambda _{\text {th }}=1.24 \times 10^{-6} m$
BETA
