1
JEE Main 2021 (Online) 27th August Morning Shift
Numerical
+4
-1
The kinetic energy of an electron in the second Bohr orbit of a hydrogen atom is equal to $${{{h^2}} \over {xma_0^2}}$$. The value of 10x is ___________. (a0 is radius of Bohr's orbit) (Nearest integer) [Given : $$\pi$$ = 3.14]
2
JEE Main 2021 (Online) 26th August Evening Shift
Numerical
+4
-1
A metal surface is exposed to 500 nm radiation. The threshold frequency of the metal for photoelectric current is 4.3 $$\times$$ 1014 Hz. The velocity of ejected electron is ____________ $$\times$$ 105 ms$$-$$1 (Nearest integer)

[Use : h = 6.63 $$\times$$ 10$$-$$34 Js, me = 9.0 $$\times$$ 10$$-$$31 kg]
3
JEE Main 2021 (Online) 25th July Evening Shift
Numerical
+4
-1
An accelerated electron has a speed of 5 $$\times$$ 106 ms$$-$$1 with an uncertainty of 0.02%. The uncertainty in finding its location while in motion is x $$\times$$ 10$$-$$9 m. The value of x is ____________. (Nearest integer)

[Use mass of electron = 9.1 $$\times$$ 10$$-$$31 kg, h =6.63 $$\times$$ 10$$-$$34 Js, $$\pi$$ = 3.14]
4
JEE Main 2021 (Online) 25th July Morning Shift
Numerical
+4
-1
A source of monochromatic radiation of wavelength 400 nm provides 1000 J of energy in 10 seconds. When this radiation falls on the surface of sodium, x $$\times$$ 1020 electrons are ejected per second. Assume that wavelength 400 nm is sufficient for ejection of electron from the surface of sodium metal. The value of x is ______________. (Nearest integer)

(h = 6.626 $$\times$$ 10$$-$$34 Js)