Physics Chapter 13 Past Paper Questions PDF

# Chapter 12 - Atoms ## Objective * **Bihar Inter Exam 2025** * **Science Crash Course** * **Live Class** * **Video** * **PDF Notes** * **Test Series** * **One Shot** * **Qns. Bank** * **Series** **Price**: Rs 299/- **Install TARGET BOARD App** **Mob No-8114532021, 9263991125** ## Question...

# Chapter 12 - Atoms ## Objective * **Bihar Inter Exam 2025** * **Science Crash Course** * **Live Class** * **Video** * **PDF Notes** * **Test Series** * **One Shot** * **Qns. Bank** * **Series** **Price**: Rs 299/- **Install TARGET BOARD App** **Mob No-8114532021, 9263991125** ## Question 1 What event related to α-particles was used in the experiment to find out the structure of the atom? **(a)** Reflection **(b)** Refraction **(c)** Diffraction **(d)** **Scattering** **Explanation:** Rutherford used the scattering of alpha particles from a thin gold foil to understand the atomic structure. ## Question 2 Electrons revolve around the nucleus due to which force? **(a)** Nuclear force **(b)** Gravitational force **(c)** Coulomb force **(d)** None of them **Explanation:** The electrostatic force of attraction between the positively charged nucleus and negatively charged electrons keeps them in their orbits. ## Question 3 Rutherford's Scattering Experiment proved the existence of which of the following? **(a)** Negatively charged nucleus **(b)** **Positively charged nucleus** **(c)** Neutrons in nucleus **(d)** A uniform distribution of positive charge in the atom **Explanation:** The scattering of alpha particles at large angles indicated the presence of a concentrated positively charged region in the atom - the nucleus. ## Question 4 In Rutherford's experiment, α-particles that come closest to the nucleus are: **(a)** Move straight **(b)** Slightly deflected **(c)** **Deflected at a large angle** **(d)** Stop **Explanation:** The α-particles with high kinetic energy were deflected at large angles, which indicate their close interaction with the positively charged nucleus. ## Question 5 The SI unit of Rydberg constant R is: **(a)** m **(b)** m² **(c)** **m⁻¹** **(d)** m⁻² **Explanation:** The Rydberg constant (R) is related to the wavelength of light emitted or absorbed during electronic transition in atoms. The SI unit of wavelength is meter and hence R has the unit of **m⁻¹**. ## Question 6 Bohr's frequency condition is: **(a)** E₁ – E2 = (1/2) hv **(b)** E₁ – E2 = (1/3) hv **(c)** E₁ – E2 = 3 hv **(d)** **E₁ – E2 = hv** **Explanation:** Bohr's frequency condition states that the energy difference between two energy levels (E₁ and E₂) in an atom is equal to the energy of the emitted or absorbed photon (hv). ## Question 7 A hydrogen atom is in the ground state when its electron is: **(a)** In the nucleus **(b)** Stationary **(c)** **In the lowest energy level** **(d)** Outside the atom **Explanation:** The ground state represents the lowest energy state of an atom, where the electron occupies the lowest energy level. ## Question 8 The energy difference between successive energy levels in a hydrogen atom: **(a)** Decreases as n increases **(b)** Decreases as n decreases **(c)** **Increases as n increases** **(d)** Neither increases nor decreases, where n is the principal quantum number. **Explanation:** The energy difference between successive energy levels decreases as n increases, where n is the principal quantum number, which signifies the energy level of the atom. ## Question 9 The ratio of the velocity of the electron in the first orbit of a hydrogen atom to the velocity of light is: **(a)** 1/2 **(b)** **1/137** **(c)** 2/ 137 **(d)** 1/237 ## Question 10 The ratio of kinetic energy to potential energy of an electron in a Bohr orbit of a hydrogen atom is: **(a)** 1/2 **(b)** 2 **(c)** **-1/2** **(d)** -2 ## Question 11 Which series of the hydrogen spectrum falls in the visible region: **(a)** Lyman Series → Ultraviolet **(b)** **Balmer Series → Visible** **(c)** Paschen Series → Infrared **(d)** Bracket Series → Infrared **Explanation:** The Balmer series is the only spectral series of the hydrogen atom whose transitions lie in the visible region of the electromagnetic spectrum. ## Question 12 Which series of the hydrogen spectrum falls in the ultraviolet region? **(a)** **Lyman series** **(b)** Balmer series **(c)** Paschen series **(d)** Pfund series **Explanation:** The Lyman series of the hydrogen atom lies in the ultraviolet region of the electromagnetic spectrum. ## Question 13 A photon of energy 12.1 eV is incident on a hydrogen atom. To which orbit will its electron jump? **(a)** 2nd **(b)** **3rd** **(c)** 4th **(d)** 5th **Explanation:** The energy difference between the first and second energy levels of the hydrogen atom is about 10.2 eV and the energy difference between the first and third energy levels is about 12.1 eV. Therefore, the photon will excite the hydrogen atom from its ground state to the third energy levels. ## Question 14 The energy of an electron in a specific orbit of an atom with atomic number Z is proportional to: **(a)** Z **(b)** **Z²** **(c)** Z⁻¹ **(d)** Z⁻² **Explanation:** In a hydrogen-like atom, the energy of an electron in an orbit is proportional to the square of the atomic number **(Z²)**. ## Question 15 The energy of the electron in the first Bohr orbit of a hydrogen atom is -13.6 eV. What will be its energy in the second Bohr orbit? **(a)** **-3.4 eV** **(b)** -6.8 eV **(c)** -27.2 eV **(d)** +3.4 eV **Explanation:** The energy of an electron in the n-th Bohr orbit of a hydrogen atom is given by: E = -13.6/n² eV. Therefore, for n = 2 (second orbit), the energy is: E = -13.6 / (2)² = - 3.4 eV. ## Question 16 Electrons in an atom can revolve only in those orbits whose angular momentum is: **(a)** h/2π **(b)** 2πh **(c)** h **(d)** None of them **Explanation:** Bohr's quantization condition for angular momentum states that the angular momentum of an electron revolving around the nucleus can only be quantized in discrete values which are multiples of h/(2π). ## Question 17 What is the minimum angular momentum of an electron in a hydrogen atom? **(a)** h/π Js **(b)** **h / (2π) Js** **(c)** hλ Js **(d)** 2πh Js **Explanation:** The minimum angular momentum of the electron occurs when the principal quantum number n = 1. ## Question 18 If the radius of the first orbit of a hydrogen atom is 5.3 × 10⁻¹¹m, what is the radius of the second orbit? **(a)** 1.12 Å **(b)** **2.12 Å** **(c)** 3.22 Å **(d)** 4.54 Å **Explanation:** The radius of the n-th Bohr orbit of hydrogen atom is rn = n²r₁. Therefore, for n = 2, the radius is: r₂ = (2)² × 5.3 × 10⁻¹¹ m = 2.12 Å. ## Question 19 If the radius of the Bohr's first orbit is r, then the radius of the second orbit is: **(a)** 2r **(b)** **4r** **(c)** r/2 **(d)** r/4 **Explanation:** The radius of the n-th orbit in a Bohr atom is proportional to n². Therefore, for n = 2 (second orbit), the radius is 4 times the radius of the first orbit, which is r. ## Answer Key ``` 1 D 2 C 3 B 4 C 5 C 6 D 7 C 8 C 9 B 10 C 11 B 12 A 13 B 14 B 15 A 16 A 17 B 18 B 19 B ``` ## Answers * **Question 1:** Quantum condition * **Question 2:** Transition * **Question 3:** Excitation level and excitation energy/potential * **Question 4:** Ionization Potential/Energy * **Question 5:** The ionization energy of a hydrogen-like atom with atomic number 2 and its electron in the second orbit is -3.4 eV. * **Question 6:** **Rutherford's model:** * Nearly the entire mass and all the positive charge of an atom are concentrated in a very small volume called the nucleus. * The nucleus has diameter of the order of 10⁻¹⁵ m, which is about 1/10,000 of the size of the whole atom. * Electrons revolve around the nucleus in various orbits, but these orbits have no specific radius or energy. * The electrons have high kinetic energies and the space occupied by the electrons is 10⁴ times more than the nucleus, so most of the atom is empty space. **Drawbacks of Rutherford's model:** * **Problem in explaining the stability of an atom:** The revolving electron should emit energy in the form of EM radiations and the atom should eventually collapse. * **The model could not explain the line spectrum observed in the hydrogen atom.** * **Question 7:** **Homework:** The details of the atomic spectrum of elements are not explained.