NEET Structure of Atom — Set 3

Question 1

A proton has a de Broglie wavelength of $ 1.5 \times 10^{-12} \, \text{m} $. What is its kinetic energy? ($ h = 6.626 \times 10^{-34} \, \text{J s} $, $ m_p = 1.67 \times 10^{-27} \, \text{kg} $)

Accepted Answer

$ v = \frac{h}{m\lambda} = \frac{6.626 \times 10^{-34}}{1.67 \times 10^{-27} \times 1.5 \times 10^{-12}} = 2.645 \times 10^5 \, \text{m s}^{-1} $. $ KE = \frac{1}{2} m v^2 = \frac{1}{2} \times 1.67 \times 10^{-27} \times (2.645 \times 10^5)^2 = 5.837 \times 10^{-17} \, \text{J} $.

Question 2

How many neutrons are present in an atom with atomic number 19 and mass number 39?

Accepted Answer

Neutrons = mass number - atomic number = 39 - 19 = 20.

Question 3

A metal has a threshold wavelength of $ 500 \, \text{nm} $. What is the stopping potential when irradiated with light of wavelength $ 400 \, \text{nm} $? ($ h = 6.626 \times 10^{-34} \, \text{J s} $, $ c = 3.0 \times 10^8 \, \text{m s}^{-1} $, $ e = 1.6 \times 10^{-19} \, \text{C} $)

Accepted Answer

$ W_0 = \frac{hc}{\lambda_0} = \frac{6.626 \times 10^{-34} \times 3.0 \times 10^8}{500 \times 10^{-9}} = 3.9756 \times 10^{-19} \, \text{J} $. $ E = \frac{hc}{\lambda} = \frac{6.626 \times 10^{-34} \times 3.0 \times 10^8}{400 \times 10^{-9}} = 4.9695 \times 10^{-19} \, \text{J} $. $ KE = 4.9695 \times 10^{-19} - 3.9756 \times 10^{-19} = 9.939 \times 10^{-20} \, \text{J} $. $ V_s = KE / e = 0.621 \, \text{V} $.

NEET Chemistry: Structure of Atom — Practice Set 3

Q1. A proton has a de Broglie wavelength of \( 1.5 \times 10^{-12} \, \text{m} \). What is its kinetic energy? (\( h = 6.626 \times 10^{-34} \, \text{J s} \), \( m_p = 1.67 \times 10^{-27} \, \text{kg} \))

Q2. How many neutrons are present in an atom with atomic number 19 and mass number 39?

Q3. A metal has a threshold wavelength of \( 500 \, \text{nm} \). What is the stopping potential when irradiated with light of wavelength \( 400 \, \text{nm} \)? (\( h = 6.626 \times 10^{-34} \, \text{J s} \), \( c = 3.0 \times 10^8 \, \text{m s}^{-1} \), \( e = 1.6 \times 10^{-19} \, \text{C} \))

Q4. A proton and an alpha particle have the same de Broglie wavelength. What is the ratio of their velocities? (\( m_p = 1.67 \times 10^{-27} \, \text{kg} \), \( m_{\alpha} = 6.64 \times 10^{-27} \, \text{kg} \))

Q5. How many electrons in an atom can have the quantum numbers \( n = 5 \) and \( l = 2 \)?

Q6. An atom has an electronic configuration of \( 1s^2 2s^2 2p^6 3s^2 3p^6 3d^2 \). What is its atomic number?

Q7. The energy of an electron in the first orbit of \( \text{Li}^{2+} \) is \( -122.4 \, \text{eV} \). What is the ionization energy from the third orbit? (\( 1 \, \text{eV} = 1.6 \times 10^{-19} \, \text{J} \))

Q9. An atom has 26 protons, 30 neutrons, and 24 electrons. What is its net charge?

Q10. Which of the following particles has the smallest de Broglie wavelength if all move at the same speed?