List of top Physics Questions asked in CBSE CLASS XII

Explain briefly the formation of diffusion current and drift current in a p-n junction diode.
Explain the following observations using Einstein’s photoelectric equation:
(a) Photoelectric emission does not occur from a surface when the frequency of the light incident on it is less than a certain minimum value.
(b) It is the frequency, and not the intensity of the incident light which affects the maximum kinetic energy of the photoelectrons.
(c) The cut-off voltage \( V_0 \) versus frequency \( \nu \) of the incident light curve is a straight line with a slope \( \frac{h}{e} \).
What are majority and minority charge carriers of p-type and n-type semiconductors?
A battery of emf E and internal resistance r is connected to an external resistance R.
(I) Expression for current I and maximum current:.
(II) Terminal voltage V and its maximum value:.
State any three characteristics of electromagnetic waves.
Expression for internal resistance in terms of I1, I2, R1, R2:
Two insulated long straight wires, each carrying \( 2.0 \ \text{A} \) current are kept along \( xx' \) and \( yy' \) axes as shown in the figure. Find the magnitude and direction of the resultant magnetic field at point \( P(4\,\text{m},\,5\,\text{m}) \).
Two insulated long straight wires, each carrying 2.0
Two coils ‘1’ and ‘2’ are placed close to each other as shown in the figure. Find the direction of induced current in coil ‘1’ in each of the following situations, justifying your answers:
Two coils ‘1’ and ‘2’ are placed

(a) Coil ‘2’ is moving towards coil ‘1’.
(b) Coil ‘2’ is moving away from coil ‘1’.
(c) The resistance connected with coil ‘2’ is increased keeping both the coils stationary.
Write vector form of Biot–Savart law.
The figure shows the plot of current through a cross-section of wire over two different time intervals. Compare the charges Q1 and Q2 that pass through the cross-section during these time intervals.
plot of current through a cross-section
Briefly explain how and where the displacement current exists during the charging of a capacitor.
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.
An equiconvex lens is made of glass of refractive index 1.55. If the focal length of the lens is 15.0 cm, calculate the radius of curvature of its surfaces.
Calculate the mass of an $\alpha$-particle in atomic mass unit (u).
Given: Mass of a normal helium atom = \( 4.002603 \ \text{u} \)
Mass of carbon atom = \( 1.9926 \times 10^{-26} \ \text{kg} \)
Find the angle of diffraction (in degrees) for first secondary maximum of the pattern due to diffraction at a single slit. The width of the slit and wavelength of light used are 0.55 mm and 550 nm, respectively.
Derive an expression for the resistivity of a conductor in terms of number density of free electrons and relaxation time.
Two cells of emf 10 V each, two resistors of 20 \( \Omega \) and 10 \( \Omega \), and a bulb B of 10 \( \Omega \) resistance are connected together as shown in the figure. Find the current that flows through the bulb.
Two cells of emf 10 V each, two resistors
In an intrinsic semiconductor, carrier’s concentration is \( 5 \times 10^8 \ \text{m}^{-3} \). On doping with impurity atoms, the hole concentration becomes \( 8 \times 10^{12} \ \text{m}^{-3} \).

[(a)] Identify (i) the type of dopant and (ii) the extrinsic semiconductor so formed.

[(b)] Calculate the electron concentration in the extrinsic semiconductor.
Two statements are given, one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the codes (A), (B), (C), and (D) as given below.
Assertion (A): For monochromatic incident radiation, the emitted photoelectrons from a given metal have speed ranging from zero to a certain maximum value.
Reason (R): Each metal has a definite work function.
In the given figure, three identical bulbs P, Q, and S are connected to a battery.
three identical bulbs P, Q, and S

[(i)] Compare the brightness of bulbs P and Q with that of bulb S when key K is closed.

[(ii)] Compare the brightness of the bulbs S and Q when the key K is opened.
Justify your answer in both cases.
Choose the correct statement:
Two statements are given, one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the codes (A), (B), (C), and (D) as given below.
Assertion (A): A series LCR circuit behaves as a pure resistive circuit at resonance.
Reason (R): At resonance, \( X_L = X_C \) gives \( \omega = \frac{1}{\sqrt{LC}} \).
Which of the following is an electrical conductor at room temperature?
A beam of red light and a beam of blue light have equal intensities. Which of the following statements is true?
Two statements are given, one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the codes (A), (B), (C), and (D) as given below.
Assertion (A): In double slit experiment, if one slit is closed, diffraction pattern due to the other slit will appear on the screen.
Reason (R): For interference, at least two waves are required.