Dual Nature, Atoms & Nuclei · JEE Main previous year questions

2021 30 questions

1. Q502021 · 26 Feb 2021 · Shift 2

   A radioactive sample is undergoing $\alpha$ decay. At any time $t_1$, its activity is A and another time $t_2$, the activity is $\frac{A}{5}$. What is the average life time for the sample?

   1. A.$\frac{\ln 5}{t_2-t_1}$
   2. B.$\frac{\ln (t_2+t_1)}{2}$
   3. C.$\frac{t_1-t_2}{\ln 5}$
   4. D.$\frac{t_2-t_1}{\ln 5}$
   Show answer

   Answer: D

2. Q592021 · 26 Feb 2021 · Shift 2· Numerical answer

   Two streams of photons, possessing energies equal to twice and ten times the work function of metal are incident on the metal surface successively. The value of ratio of maximum velocities of the photoelectrons emitted in the two respective cases is x : y. The value of x is ___________.

   Show answer

   Answer: 1

3. Q342021 · 25 Feb 2021 · Shift 2

   An electron of mass $m_e$ and a proton of mass $m_p=1836m_e$ are moving with the same speed. The ratio of their de Broglie wavelength $\frac{{\lambda }_{electron}}{{\lambda }_{proton}}$ will be :

   1. A.1
   2. B.1836
   3. C.$\frac{1}{1836}$
   4. D.918
   Show answer

   Answer: B

4. Q492021 · 25 Feb 2021 · Shift 2

   The stopping potential for electrons emitted from a photosensitive surface illuminated by light of wavelength 491 nm is 0.710 V. When the incident wavelength is changed to a new value, the stopping potential is 1.43 V. The new wavelength is :

   1. A.400 nm
   2. B.329 nm
   3. C.309 nm
   4. D.382 nm
   Show answer

   Answer: D

5. Q562021 · 25 Feb 2021 · Shift 2· Numerical answer

   The wavelength of an X-ray beam is $10\text{A˚}$. The mass of a fictitious particle having the same energy as that of the X-ray photons is $\frac{x}{3}h\text{ kg}$. The value of x is ______ . (h = Planck's constant)

   Show answer

   Answer: 10