1
JEE Main 2020 (Online) 3rd September Morning Slot
+4
-1
Out of Syllabus
In a radioactive material, fraction of active material remaining after time t is 9/16. The fraction that was remaining after t/2 is
A
$${3 \over 4}$$
B
$${4 \over 5}$$
C
$${3 \over 5}$$
D
$${7 \over 8}$$
2
JEE Main 2020 (Online) 2nd September Evening Slot
+4
-1
In a hydrogen atom the electron makes a transition from (n + 1)th level to the nth level. If n >> 1, the frequency of radiation emitted is proportional to :
A
$${1 \over n}$$
B
$${1 \over {{n^2}}}$$
C
$${1 \over {{n^3}}}$$
D
$${1 \over {{n^4}}}$$
3
JEE Main 2020 (Online) 2nd September Morning Slot
+4
-1
In a reactor, 2 kg of 92U235 fuel is fully used up in 30 days. The energy released per fission is 200 MeV. Given that the Avogadro number, N = 6.023 $$\times$$ 1026 per kilo mole and 1 eV = 1.6 × 10–19 J. The power output of the reactor is close to
A
125 MW
B
60 MW
C
54 MW
D
35 MW
4
JEE Main 2020 (Online) 9th January Evening Slot
+4
-1
The energy required to ionise a hydrogen like ion in its ground state is 9 Rydbergs. What is the wavelength of the radiation emitted when the electron in this ion jumps from the second excited state to the ground state ?
A
35.8 nm
B
11.4 nm
C
8.6 nm
D
24.2 nm
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