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JEE Main 12 Apr 2019 Paper 2 Solved Paper
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© examsnet.com
Question : 7
Total: 90
Half lives of two radio active nuclei A and B are 10 minutes and 20 minutes, respectively. If , initially a sample has equal number of nuclei, then after 60 minutes, the ratio of decayed, the ratio of decayed numbers of nuclei A and B will be:
1:8
9:8
8:1
3:8
Validate
Solution:
Initial
A
B
No
No
T
1
2
10 min
20 min
t
60 min
60 min
n=
6
T
1
2
3
T
1
2
N
=
N
0
e
−
λ
t
N
d
e
c
c
a
t
e
d
=
N
0
−
N
=
N
0
(
1
−
e
λ
t
)
N
1
N
2
=
1
−
e
−
ln
2
(
60
)
10
1
−
e
−
ln
2
(
60
)
20
=
0.984375
0.825
N
1
N
2
=
1.125
⇒
N
1
N
2
=
9
8
© examsnet.com
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