List of top Physics Questions asked in CBSE CLASS XII

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.

Why electric field $\vec{E}$ at a point on an equipotential surface must be perpendicular to the surface at that point ?}

Consider the following nuclides : $^{12}_6\text{C}$, $^{198}_{80}\text{Hg}$, $^{14}_6\text{C}$, $^{197}_{79}\text{Au}$. Group them into isotopes and isotones.

Explain the statement : “Current is a scalar although we represent current with an arrow”.

Name the electromagnetic waves which are used (ii) in remote switches for TV sets. Also write their wavelength range.

Find ratio ($\lambda_a/\lambda_p$) of the de Broglie wavelength $\lambda_a$ and $\lambda_p$ associated respectively with an alpha particle and a proton, if they are moving with the same kinetic energy.

Two long straight parallel conductors A and B carrying steady currents $I_a$ and $I_b$ in the same direction are separated by a distance d. Deduce the expressions for the force acting on length L of conductor B due to conductor A and show it in figure. Write the expression for the force acting on length L of conductor A due to conductor B and show that it follows Newton's third law.

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 ($\lambda_a/\lambda_p$) of the de Broglie wavelength $\lambda_a$ and $\lambda_p$ associated respectively with an alpha particle and a proton, just after they are accelerated through the same potential difference.

Calculate the de Broglie wavelength associated with an electron revolving in the second excited state of hydrogen atom. The ground state energy of the hydrogen atom is – 13.6 eV. Take $m_e = 9 \times 10^{-31}$ kg, $h = 6.6 \times 10^{-34}$ J.s.

Name the electromagnetic waves which are used as a diagnostic tool in medicine. Also write their wavelength range.

Define mutual inductance of a pair of coils. Write its SI unit.

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.

Calculate the temperature at which the resistance of a conductor becomes 20% more than its resistance at $27^\circ\text{C}$. The value of the temperature coefficient of resistance of the material of conductor is $2.0 \times 10^{-4} ^\circ\text{C}^{-1}$.

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) : 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.

Write two points of difference between intrinsic and extrinsic semiconductors.

A ray of light is incident on the face of a triangular prism of refracting angle $60^\circ$ and it just suffers total internal reflection at the other face. Find the angle of incidence for the ray if the refractive index of the material of the prism is $\sqrt{2}$.

The figure shows the variation of capacitive reactance ($X_C$) of two ideal capacitors of capacitances $C_1$ & $C_2$ with the reciprocal of angular frequency ($1/\omega$) of ac source. The value of $C_1/C_2$ is

Assertion (A) : On increasing the intensity of incident light of frequency $\nu$ ($> \nu_0$) on a photosensitive surface, the photocurrent increases.
Reason (R) : The stopping potential for a photosensitive surface increases with increase of frequency $\nu$ ($> \nu_0$) of incident light.

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.

A galvanometer of resistance $27 \Omega$ is converted into an ammeter of range (0 – 10 mA) using a resistance of $3 \Omega$. The galvanometer will show full scale deflection for a current of about –

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 a electric device when connected to a dc source of voltage V is proportional to its resistance.

The magnetic flux $\phi$ (in Wb) linked with a coil is related to time t (in s) as
$\phi = 5 At^2 + Bt - 2C$
The SI units of A and B are respectively

A straight conductor lies along x-axis and carries a current of 2 A along +x direction. The magnetic field at a point (0, 40 cm, 0) due to 1 cm length of conductor centered at the origin points along.