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1
JEE Main 2021 (Online) 16th March Evening Shift
MCQ (Single Correct Answer)
+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
2
JEE Main 2021 (Online) 26th February Evening Shift
MCQ (Single Correct Answer)
+4
-1
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?
A
$${{\ln 5} \over {{t_2} - {t_1}}}$$
B
$${{\ln ({t_2} + {t_1})} \over 2}$$
C
$${{{t_1} - {t_2}} \over {\ln 5}}$$
D
$${{{t_2} - {t_1}} \over {\ln 5}}$$
3
JEE Main 2021 (Online) 26th February Morning Shift
MCQ (Single Correct Answer)
+4
-1
If $$\lambda$$1 and $$\lambda$$2 are the wavelengths of the third member of Lyman and first member of the Paschen series respectively, then the value of $$\lambda$$1 : $$\lambda$$2 is :
A
7 : 135
B
7 : 108
C
1 : 9
D
1 : 3
4
JEE Main 2021 (Online) 25th February Evening Shift
MCQ (Single Correct Answer)
+4
-1
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An electron of mass me and a proton of mass mp = 1836 me are moving with the same speed. The ratio of their de Broglie wavelength $${{{}^\lambda electron} \over {{}^\lambda proton}}$$ will be :
A
1
B
1836
C
$${1 \over {1836}}$$
D
918
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