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JEE Main 2021 (Online) 27th July Morning Shift
Numerical
+4
-1
A radioactive sample has an average life of 30 ms and is decaying. A capacitor of capacitance 200 $$\mu$$F is first charged and later connected with resistor 'R'. If the ratio of charge on capacitor to the activity of radioactive sample is fixed with respect to time then the value of 'R' should be _____________ $$\Omega$$.
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JEE Main 2021 (Online) 27th July Morning Shift
Numerical
+4
-1
A transistor is connected in common emitter circuit configuration, the collector supply voltage is 10 V and the voltage drop across a resistor of 1000 $$\Omega$$ in the collector circuit is 0.6 V. If the current gain factor ($$\beta$$) is 24, then the base current is _____________ $$\mu$$A. (Round off to the Nearest Integer)
3
JEE Main 2021 (Online) 25th July Evening Shift
Numerical
+4
-1
A light beam of wavelength 500 nm is incident on a metal having work function of 1.25 eV, placed in a magnetic field of intensity B. The electrons emitted perpendicular to the magnetic field B, with maximum kinetic energy are bent into circular are of radius 30 cm. The value of B is ___________ $$\times$$ 10$$-$$7 T.

Given hc = 20 $$\times$$ 10$$-$$26 J-m, mass of electron = 9 $$\times$$ 10$$-$$31 kg
A certain metallic surface is illuminated by monochromatic radiation of wavelength $$\lambda$$. The stopping potential for photoelectric current for this radiation is 3V0. If the same surface is illuminated with a radiation of wavelength 2$$\lambda$$, the stopping potential is V0. The threshold wavelength of this surface for photoelectric effect is ____________ $$\lambda$$.