1
JEE Main 2019 (Online) 11th January Morning Slot
+4
-1
A hydrogen atom, initially in the ground state is excited by absorbing a photon of wavelength 980$$\mathop A\limits^ \circ$$. The radius of the atom in the excited state, in terms of Bohr radius a0 will be : (hc = 12500 eV$$\mathop A\limits^ \circ$$)
A
4a0
B
9a0
C
25a0
D
16a0
2
JEE Main 2019 (Online) 10th January Evening Slot
+4
-1
Consider the nuclear fission

Ne20 $$\to$$ 2He4 + C12

Given that the binding energy/ nucleon of Ne20, He4 and C12 are, respectively, 8.03 MeV, 7.07 MeV and 7.86 MeV, identify the correct statement -
A
8.3 MeV energy will be released
B
energy of 11.9 MeV has to be supplied
C
energy of 12.4 MeV will be supplied
D
energy of 3.6 MeV will be released
3
JEE Main 2019 (Online) 10th January Morning Slot
+4
-1
Using a nuclear counter the count rate of emitted particles from a radioactive source is measured. At t = 0 it was 1600 counts per second and t = 8 seconds it was 100 counts per second. The count rate observed, as counts per second, at t = 6 seconds is close to -
A
200
B
150
C
400
D
360
4
JEE Main 2019 (Online) 9th January Evening Slot
+4
-1
At a given instant, say t = 0, two radioactive substance A and B have equal activities. the ratio $${{{R_B}} \over {{R_A}}}$$ of their activities after time t itself decays with time t as e$$-$$3t. If the half-life of A is ln2, the half-life of B is :
A
4ln2
B
$${{\ln 2} \over 2}$$
C
$${{\ln 2} \over 4}$$
D
2ln2
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