1
JEE Main 2021 (Online) 16th March Morning Shift
Numerical
+4
-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 _______$$\mathop A\limits^o$$. (Round off to the Nearest Integer).

[ Use : $$\sqrt 3$$ = 1.73, h = 6.63 $$\times$$ 10$$-$$34 Js

me = 9.1 $$\times$$ 10$$-$$31 kg; c = 3.0 $$\times$$ 108 ms$$-$$1; 1eV = 1.6 $$\times$$ 10$$-$$19 J]
2
JEE Main 2021 (Online) 26th February Evening Shift
Numerical
+4
-1
A ball weighing 10 g is moving with a velocity of 90 ms$$-$$1. If the uncertainty in its velocity is 5%, then the uncertainty in its position is ___________ $$\times$$ 10$$-$$33 m. (Rounded off to the nearest integer)

[Given : h = 6.63 $$\times$$ 10$$-$$34 Js]
3
JEE Main 2021 (Online) 25th February Evening Shift
Numerical
+4
-1
Electromagnetic radiation of wavelength 663 nm is just sufficient to ionise the atom of metal A. The ionization enegy of metal A in kJ mol$$-$$1 is __________. (Rounded off to the nearest integer)

[h = 6.63 $$\times$$ 10$$-$$34 Js, c = 3.00 $$\times$$ 108 ms$$-$$1, NA = 6.02 $$\times$$ 1023 mol$$-$$1]
4
JEE Main 2021 (Online) 25th February Evening Shift
Numerical
+4
-1
Among the following, number of metal/s which can be used as electrodes in the photoelectric cell is _________. (Integer answer)

(A) Li

(B) Na

(C) Rb

(D) Cs
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