List of top Physics Questions asked in CBSE CLASS XII

Prove that, in Bohr model of hydrogen atom as principal quantum number \(n\) becomes large, the energy levels get closer and closer.
Explain the statement: “Current is a scalar although we represent current with an arrow”.
Two point charges \(-q\) and \(+q\) are located at points \((-a, 0, 0)\) and \((a, 0, 0)\) respectively. Find the electrostatic potential at point \((x, 0, 0)\) where \(x \gg a\).
State Bohr’s second postulate and mention its significance.
A long solenoid of radius \(R\) and length \(L\) has \(n\) turns per unit length. A circular loop of radius \(r(<R)\) is placed inside at the centre of the solenoid such that its axis coincides with the axis of the solenoid. Obtain the mutual inductance of the solenoid and the loop.
Find ratio \( \left(\frac{\lambda_a}{\lambda_p}\right) \) of the de Broglie wavelength \( \lambda_a \) and \( \lambda_p \) associated respectively with an alpha particle and a proton,
(i) if they are moving with the same kinetic energy.
(ii) just after they are accelerated through the same potential difference.
A ray of light in air is incident at angle \(i\) on a face of an equilateral glass prism and is refracted through the prism. As \(i\) is varied, it is observed that the ray undergoes minimum deviation, when the \(i\) is three-fourth of the angle of the prism. Calculate the speed of light in the prism.
Consider the following nuclides : \(^{12}_{6}C,\ ^{198}_{80}Hg,\ ^{14}_{6}C,\ ^{197}_{79}Au\). Group them into isotopes and isotones.
How does the size of a nucleus depend on its mass number A? Hence prove that the density of nucleus is a constant, independent of A, for all nuclei.
A heating element using nichrome is connected to a 220 V supply. Initially it draws a current of 2.9 A. After some time, the current attains a steady value of 2.5 A. Find the steady temperature of the heating element if the room temperature is 27 \(^{\circ}\)C. The temperature coefficient of resistance of nichrome is \(1.7 \times 10^{-4}\ ^{\circ}\text{C}^{-1}\).
A 5 cm long pencil is placed along the principal axis of a concave mirror of focal length 20 cm such that its nearest end is at a distance of 25 cm from the mirror. Calculate the length of the image of the pencil.
An electric field \( \vec{E} = E_0 \hat{i} \) exists in a region of space. Draw three equipotential surfaces in the region.
In a Young’s double-slit experiment, a beam of light consisting of two wavelengths 500 nm and 600 nm is used. The interference fringes are observed at a screen placed 1.8 m away from the plane of slits (slit separation 0.3 mm). Calculate the least distance from the central maximum where the bright fringes due to both the wavelengths coincide.
Assertion (A): Light added to light can produce darkness. Reason (R): When two coherent light waves interfere, there is darkness at position of destructive interference.
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.
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
Write two points of difference between intrinsic and extrinsic semiconductors.
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.
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.
In Bohr model, electron transitions from $n=5$ to $n=1$ emit wavelength $\lambda$. What is wavelength for transition $n=5$ to $n=2$?
A magnet with north pole down is dropped along the axis of a closed solenoid. Observed from top, the induced current is
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
The magnetic flux $\phi = 5At^{2} + Bt - 2C$ has SI units of $A$ and $B$ respectively}
Which of the following materials has positive and small value of magnetic susceptibility?
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