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UPSEE 2019 Solved Paper
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© examsnet.com
Question : 47
Total: 150
The half-life time of a radioactive sample is
5
m
i
n
. The amount of substance decayed in 20 min will be
93.75
%
75
%
25
%
6.25
%
Validate
Solution:
Given, half-life
T
1
∕
2
=
5
m
i
n
and time
t
=
20
m
i
n
As, fraction remains after
n
th half-life,
N
N
0
=
(
1
2
)
n
=
(
1
2
)
t
∕
T
1
∕
2
⇒
N
N
0
=
(
1
2
)
20
5
=
(
1
2
)
4
⇒
N
N
0
=
1
16
Now, \% amount of substance decayed in
20
m
i
n
,
X
=
N
0
−
N
N
0
×
100
=
(
16
−
1
)
16
×
100
=
15
16
×
100
X
=
93.75
%
© examsnet.com
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