List of top Physics Questions asked in CBSE CLASS XII

Calculate the value of the current passing through the battery in the given circuit diagram.
A convex lens of focal length 10 cm, a concave lens of focal length 15 cm, and a third lens of unknown focal length are placed coaxially in contact. If the focal length of the combination is +12 cm, find the nature and focal length of the third lens, if all lenses are thin. Will the answer change if the lenses were thick?
A capacitor and an inductor are connected in series across an ac source of voltage of variable frequency. The frequency is increased continuously. The nature of the circuit before and after the resonance will be:
Write the mathematical forms of three postulates of Bohr’s theory of the hydrogen atom. Using them prove that, for an electron revolving in the \( n \)-th orbit,
(a) the radius of the orbit is proportional to \( n^2 \), and
(b) the total energy of the atom is proportional to \( \frac{1}{n^2} \).
Explain the transmission of optical signal through an optical fiber with a diagram.
A double slit set-up was initially placed in a tank filled with water and the interference pattern was obtained using a laser light. When water is replaced by a transparent liquid of refractive index \( n>n_{\text{water}} \), what will be the effect on the following?
(a) Speed, frequency and wavelength of the light of laser beam.
(b) The fringe width, shape of interference fringes and shift in the position of central maximum.
In an n-type semiconductor, electron-hole combination is a continuous process at room temperature. Yet the electron concentration is always greater than the hole concentration in it. Explain.
An electron of mass \(m\) and charge \(-e\) is revolving anticlockwise around the nucleus of an atom. (a) Obtain the expression for the magnetic dipole moment \(\mu\) of the atom.

(b) If \( \vec{L} \) is the angular momentum of the electron, show that:
\[ \vec{\mu} = -\frac{e}{2m} \vec{L} \]

A tank is filled with a liquid of refractive index \( \sqrt{2} \), up to a height of 30 cm. A tiny bulb is glowing at the bottom of the tank. Calculate the diameter of an opaque disc floating symmetrically on the liquid surface that can cut off completely the light from the bulb that comes out of the liquid surface.
Find the intensity at a point on the screen in Young’s double slit experiment, at which the interfering waves of intensity \( I_0 \) each, have a path difference of (i) \( \frac{\lambda}{3} \), and (ii) \( \frac{\lambda}{2} \).
Two convex lenses A and B, each of focal length 10.0 cm, are mounted on an optical bench at 50.0 cm and 70.0 cm respectively. An object is mounted at 20.0 cm. Find the nature and position of the final image formed by the combination.
Assertion (A): The deflection in a galvanometer is directly proportional to the current passing through it.
Reason (R): The coil of a galvanometer is suspended in a uniform radial magnetic field.
Let \( \lambda_e \), \( \lambda_p \), and \( \lambda_d \) be the wavelengths associated with an electron, a proton, and a deuteron, all moving with the same speed. Then the correct relation between them is:
You are required to design an air-filled solenoid of inductance 0.016 H having a length 0.81 m and radius 0.02 m. The number of turns in the solenoid should be:

Obtain an expression for the electric field \( \vec{E} \) due to a dipole of dipole moment \( \vec{p} \) at a point on its equatorial plane and specify its direction.
Hence, find the value of electric field:

  1. at the centre of the dipole (\( r = 0 \))
  2. at a point \( r \gg a \), where \( 2a \) is the length of the dipole.
A metal sheet is inserted between the plates of a parallel plate capacitor of capacitance C. If the sheet partly occupies the space between the plates, the capacitance:
The given diagram exhibits the relationship between the wavelength of the electromagnetic waves and the energy of photons associated with them. The three points P, Q, and R marked on the diagram may correspond respectively to:
relationship between the wavelength of the electromagnetic waves
The de Broglie wavelength associated with an electron moving with energy 5 eV is:
A conductor of length l and area of cross-section A is connected across an ideal battery of emf V . Derive the formula for the current density in terms of relaxation time τ
A body acquires charge \( 8.0 \times 10^{-12} \, \text{C} \). The mass of the body:
Assertion (A): A charged particle is moving with velocity \( v \) in \( x \)-\( y \) plane, making an angle \( \theta \) (\( 0<\theta<90^\circ \)) with \( x \)-axis. If a uniform magnetic field is applied in the region, along \( y \)-axis, the particle will move in a helical path with its axis parallel to \( x \)-axis.
Reason (R): The direction of the magnetic force acting on a charged particle moving in a magnetic field is along the velocity of the particle.
A parallel plate capacitor has plate area \( A \) and plate separation \( d \). Half of the space between the plates is filled with a material of dielectric constant \( K \) in two ways as shown in the figure. Find the values of the capacitance of the capacitors in the two cases. parallel plate capacitor
A beam of red light and a beam of blue light have equal intensities. Which of the following statements is true?
The work function of a material is 2.21 eV. Which of the following cannot produce photoelectrons from it?
In which cases does a charged particle not experience a force in a magnetic field?