JEE Main 2026 — Physics Modern Physics
When a light of a given wavelength falls on a metallic surface the stopping potential for photoelectrons is 3.2 V. If a second light having wavelength twice of first light is used, the stopping potential drops to 0.7 V. The wavelength of first light is ____ m. (h=6.63×10−34 J.s,e=1.6×10−19C,c=3×108 m/s)
Held on 24 Jan 2026 · Verified 6 Jul 2026.
2.5×10−7
2.2×10−8
3.1×10−7
2.9×10−8
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An electron is travelling with a velocity $v$ in free space and when it enters a medium, its velocity is reduced by $20\%$. The de Broglie wavelength of electron in the medium is $\alpha\lambda_0$, where $\lambda_0$ is its de Broglie wavelength in free space. The value of $\alpha$ is _______.
The maximum rated power of the LED is $2$ mW and it is used in the circuit with input voltage of $5$ V as shown in the figure below. The current through resistance $R_S$ is $0.5$ mA. The minimum value of the resistance of $R_S$, to ensure that the LED is not damaged is _______ k$\Omega$. 
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A light wave described by $E=60\left[\sin \left(3 \times 10^{15}\right) t+\sin \left(12 \times 10^{15}\right) t\right]$ (in SI units) falls on a metal surface of work function 2.8 eV. The maximum kinetic energy of ejected photoelectron is (approximately) $\_\_\_\_$ eV. $\left(h=6.6 \times 10^{-34} \mathrm{~J}\right.$. s. and $\left.e=1.6 \times 10^{-19} \mathrm{C}\right)$
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