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1
JEE Main 2021 (Online) 16th March Evening Shift
+4
-1
Calculate the time interval between 33% decay and 67% decay if half-life of a substance is 20 minutes.
A
40 minutes
B
60 minutes
C
13 minutes
D
20 minutes
2
JEE Main 2021 (Online) 16th March Evening Shift
+4
-1
The de-Broglie wavelength associated with an electron and a proton were calculated by accelerating them through same potential of 100 V. What should nearly be the ratio of their wavelengths? (mp = 1.00727u me = 0.00055u)
A
41.4 : 1
B
(1860)2 : 1
C
1860 : 1
D
43 : 1
3
JEE Main 2021 (Online) 16th March Evening Shift
+4
-1
The half-life of Au198 is 2.7 days. The activity of 1.50 mg of Au198 if its atomic weight is 198 g mol$$-$$1 is, (Na = 6 $$\times$$ 1023/mol).
A
240 Ci
B
357 Ci
C
252 Ci
D
535 Ci
4
JEE Main 2021 (Online) 26th February Evening Shift
A radioactive sample is undergoing $$\alpha$$ decay. At any time t1, its activity is A and another time t2, the activity is $${A \over 5}$$. What is the average life time for the sample?
$${{\ln 5} \over {{t_2} - {t_1}}}$$
$${{\ln ({t_2} + {t_1})} \over 2}$$
$${{{t_1} - {t_2}} \over {\ln 5}}$$
$${{{t_2} - {t_1}} \over {\ln 5}}$$