List of top Physics Questions asked in CBSE CLASS XII

A point source in air is placed in front of a convex spherical glass surface ($n = 1.5$ and $R = 10$ cm). Its real image is formed at the same distance from the surface as the source. The distance of the source from the surface is:

In forward and reverse biased silicon p-n junction, the dominant mechanisms for the motion of charge carriers are:

The energy of an electron in an orbit in a hydrogen atom (Bohr model) is $-3.4$ eV. Its angular momentum in this orbit is:

Which of the following is also referred to as 'heat waves'?

In a series LCR circuit connected to an ac source of voltage $V$ and frequency $\omega$, the power loss at resonance is:

In an electromagnetic wave, the electric field ($\vec{E}$) and the magnetic field ($\vec{B}$) oscillate along x-axis and y-axis respectively. The wave is propagating along:

If $\nu_X$, $\nu_G$ and $\nu_U$ are frequencies of X-rays, Gamma-rays and UV rays respectively, then:

Two infinitely long straight conductors lie along the x-axis and y-axis in the plane of the page. If they carry current $I$ each along $+x$-axis and $+y$-axis respectively, the net magnetic field at a point with position vector $\vec{r} = (3\hat{i} + 4\hat{j})$ m will be:

Assume that the surface charge density of the Earth is 1 electron charge/m². The potential of the Earth's surface (radius 6400 km) will be:

Two point charges \(q_1 = 2.5 \times 10^{-7}\,\text{C}\) and \(q_2 = -2.5 \times 10^{-7}\,\text{C}\) are located at points \((0, 0, -15\,\text{cm})\) and \((0, 0, 15\,\text{cm})\) respectively. Find:

(a) the electric dipole moment of the system, and

(b) the magnitude and direction of the electric field at the origin \((0, 0, 0)\).

(a) Can a transformer step up or step down a dc power supply?

(b) Can a step-up transformer work as a step-down transformer?

(c) Does a step-up transformer violate the law of conservation of energy? Justify your answer.

(a) The two Kirchhoff's rules are based on law of conservation of two physical quantities. Name the quantities.

(b) Find magnitude and direction of current in 1 \(\Omega\) resistor in the given circuit.

What are microwaves? How are they produced? Give any two uses of microwaves.

A conducting rectangular loop of area 5 cm\(^{2}\) and resistance 4 \(\Omega\) is removed from a region of uniform magnetic field, acting normal to the plane of the loop. The value of induced current I in the loop varies with time t, as shown in the figure.

Find:

(a) total charge that passed through the loop

(b) change in magnetic flux through the loop

(c) magnitude of magnetic field in the region

A coil having 100 closely wound turns and area of cross-section 300 mm\(^{2}\) carries a current of 5 mA. The magnitude of the magnetic moment associated with the coil is:

In an experiment on photoelectric emission, the intensity of incident radiation is halved keeping its frequency constant. As a result:

Prove that the density of nuclear matter is same for all nuclei.

A concave mirror of radius of curvature 16 cm produces two-times enlarged real image of an object kept in front of it. Find the position of the object.

In Bohr model of hydrogen atom, calculate:

(a) the radius of the innermost electron orbit, and

(b) the speed of electron in this orbit.

A closely wound long solenoid of self-inductance L is cut into two identical solenoids. The value of self-inductance of each small solenoid will be:

Which of the following characteristics of electrons determines the current in the conductor?

A wire is gradually stretched to make it 100% longer. Its resistance will increase by:

(i) Explain the following statements giving reason:

(I) An equipotential surface through a point is normal to the electric field at that point.

(II) When a dielectric is placed in an external electric field, the electric field inside the dielectric is less than that outside it.

(III) The potential difference between the plates of a charged parallel plate capacitor decreases when its plates are brought closer.

(ii) Obtain an expression for the work done to dissociate the system of three charges \(q\), \(-4q\) and \(2q\) placed at the vertices A, B and C respectively of an equilateral triangle of side 'a'.