List of top Physics Questions asked in CBSE CLASS XII

Assertion (A): On increasing the intensity of incident light of frequency \( v(> v_0) \) on a photosensitive surface, the photocurrent increases. Reason (R): The stopping potential for a photosensitive surface increases with increase of frequency \( v(> v_0) \) of incident light.
In Bohr model, electron transitions from $n=5$ to $n=1$ emit wavelength $\lambda$. What is wavelength for transition $n=5$ to $n=2$?
Assertion (A): On forward biasing a p-n junction diode, the height of the barrier potential increases. Reason (R): In forward biasing of a p-n junction diode, the direction of the applied voltage is in the same direction as the built-in potential.
An electromagnetic wave is propagating along x-axis. At any instant, the phase difference between the electric field ($\vec{E}$) and magnetic field ($\vec{B}$) is
Assertion (A): Two electric heaters of power \( P_1 \) and \( P_2 (> P_1) \) are joined in series across a dc source of voltage \( V \). The power consumed by the combination will be less than that consumed by \( P_1 \) when connected across the same source. Reason (R): The power consumed by an electric device when connected to a dc source of voltage \( V \) is proportional to its resistance.
The figure shows the variation of capacitive reactance $X_C$ with $1/\omega$ gives two straight lines for capacitors $C_1$ and $C_2$. The ratio $C_1/C_2$ is
A galvanometer of resistance $27\ \Omega$ is converted into an ammeter of range $(0 - 10\text{ mA})$ using a resistance of $3\ \Omega$. The galvanometer will show full scale deflection for a current of about
Which of the following materials has positive and small value of magnetic susceptibility?
The magnetic flux $\phi = 5At^{2} + Bt - 2C$ has SI units of $A$ and $B$ respectively}
Magnetic field due to long wire along y-axis carrying current in -y direction at (50 cm,0,0) points along
The maximum kinetic energy of photoelectrons depends on
In Bohr model, for large $n$, spacing between consecutive orbits is proportional to
A conducting rod of length 50 cm, with one end pivoted, is rotated with angular speed of 60 rpm in a uniform magnetic field of 4.0 mT directed perpendicular to the plane of rotation of rod. Find the emf induced in the rod.
Draw a labelled diagram of a step-up transformer. State the principle on which it works and obtain the ratio of secondary voltage to primary voltage in terms of number of turns and currents in the two coils.
State Faraday’s law of electromagnetic induction.
Two metal spheres of radii $r_1$ and $r_2$ having charges $q_1$ and $q_2$ are brought in contact. Which statement is NOT correct?
A concave mirror produces a two times magnified virtual image of an object kept 10 cm in front of it. Calculate the focal length of the mirror.
Three point charges $2q$, $-2q$ and $q$ are kept at the vertices of an equilateral triangle of side $l$. The potential energy of the system is
Derive an expression for the self-inductance of an air-filled long solenoid of length \(l\) and cross-sectional area \(A\) having \(N\) turns.
The ratio of the number of turns in the primary to the secondary of an ideal transformer is \(1:5\). If \(5\) kW power at \(200\) V is supplied to the primary, find
(i) current in the primary, and
(ii) output voltage.
A dipole is placed in x-y plane such that charges \(+q\) and \(-q\) are located at \(x=a\) and \(x=b\) respectively. There exists an electric field \[ \vec E = 2\hat{i}\,\frac{N}{C} \] in the region. Calculate the force \(\vec F\) and torque \(\vec \tau\) experienced by the dipole.
Two cells of emf \(E_1\) and \(E_2\) with internal resistances \(r_1\) and \(r_2\) respectively, are connected in parallel by connecting their positive terminals together and negative terminals together. Deduce an expression for equivalent emf and equivalent internal resistance of the combination.
Using the relation for refraction at a curved spherical surface, derive the expression for lens maker's formula.
Draw a ray diagram to show the image formation by a concave mirror when the object is kept between its focus and the centre of curvature. Using this diagram, derive the mirror formula.
A parallel combination, as stated in (a) above, of two cells of emfs \(E\) and \(3E\) and internal resistances \(R\) each is connected across a resistance \(2R\). Find the current that flows through resistance \(2R\).