Science (English Medium) Class 12 - CBSE Important Questions for Physics

Plot a graph showing the variation of photoelectric current, as a function of anode potential for two light beams having the same frequency but different intensities I₁ and I₂ (I₁ > I₂). Mention its important features.

A metallic plate exposed to white light emits electrons. For which of the following colours of light, the stopping potential will be maximum?

• Assertion (A): For the radiation of a frequency greater than the threshold frequency, the photoelectric current is proportional to the intensity of the radiation.
• Reason (R): Greater the number of energy quanta available, the greater the number of electrons absorbing the energy quanta and the greater the number of electrons coming out of the metal.

Calculate the de-Broglie wavelength of the electron orbitting in the n = 2 state of hydrogen atom.

Define ionization energy.

Calculate the shortest wavelength of the spectral lines emitted in Balmer series.

[Given Rydberg constant, R = 10⁷ m^–1]

When is H_α line in the emission spectrum of hydrogen atom obtained? Calculate the frequency of the photon emitted during this transition.

Given the ground state energy E₀ = - 13.6 eV and Bohr radius a₀ = 0.53 Å. Find out how the de Broglie wavelength associated with the electron orbiting in the ground state would change when it jumps into the first excited state.

State Bohr’s postulate of hydrogen atom which successfully explains the emission lines in the spectrum of hydrogen atom. Use Rydberg formula to determine the wavelength of H_α line. [Given: Rydberg constant R = 1.03 × 10⁷ m⁻¹]

A 12.5 eV electron beam is used to bombard gaseous hydrogen at room temperature. Upto which energy level the hydrogen atoms would be excited? Calculate the wavelengths of the first member of Lyman and first member of Balmer series.

The ground state energy of a hydrogen atom is −13.6 eV. What are the kinetic and potential energies of the electron in this state?

A 12.5 eV electron beam is used to bombard gaseous hydrogen at room temperature. What series of wavelengths will be emitted?

The total energy of an electron in the first excited state of the hydrogen atom is about −3.4 eV.

What is the kinetic energy of the electron in this state?

The total energy of an electron in the first excited state of the hydrogen atom is about −3.4 eV.

What is the potential energy of the electron in this state?

The total energy of an electron in the first excited state of the hydrogen atom is about −3.4 eV.

Which of the answers above would change if the choice of the zero of potential energy is changed?

The ground state energy of hydrogen atom is – 13∙6 eV. If an electron makes a transition from an energy level – 1∙51 eV to – 3∙4 eV, calculate the wavelength of the spectral line emitted and name the series of hydrogen spectrum to which it belongs.

Find out the wavelength of the electron orbiting in the ground state of hydrogen atom.

Find the wavelength of the electron orbiting in the first excited state in hydrogen atom.

How would the ionization energy change when the electron in the hydrogen atom is replaced by a particle of mass 200 times that of the electron but having the same charge?

Using Bohr's postulates, derive the expression for the orbital period of the electron moving in the n^th orbit of hydrogen atom ?