List of top Physics Questions asked in CBSE CLASS XII

The terminology of different parts of the electromagnetic spectrum is given in the text. Use the formula \(E = hν\) (for energy of a quantum of radiation: photon) and obtain the photon energy in units of eV for different parts of the electromagnetic spectrum. In what way are the different scales of photon energies that you obtain related to the sources of electromagnetic radiation?

In a chamber, a uniform magnetic field of \(6.5 \,G \,(1 G = 10^ {–4 }T)\) is maintained. An electron is shot into the field with a speed of \(4.8 × 10^6\, m s^{–1}\) normal to the field. Obtain the frequency of revolution of the electron in its circular orbit. Does the answer depend on the speed of the electron? Explain.\((e = 1.5 × 10^{–19}C,\, m_e = 9.1×10^{–31} kg)\)
Light of wavelength 488nm is produced by an argon laser which is used in the photoelectric effect. When light from this spectral line is incident on the emitter, the stopping (cut-off) potential of photoelectrons is 0.38V. Find the work function of the material from which the emitter is made.

A short bar magnet placed with its axis at 30º with a uniform external magnetic field of 0.25 T experiences a torque of magnitude equal to             4.5 × 10-2 J. What is the magnitude of magnetic moment of the magnet?

A 600pF capacitor is charged by a 200V supply. It is then disconnected from the supply and is connected to another uncharged 600 pF capacitor. How much electrostatic energy is lost in the process?
(a) At what distance should the lens be held from the card sheet in Exercise 9.22 in order to view the squares distinctly with the maximum possible magnifying power? (b) What is the magnification in this case? (c) Is the magnification equal to the magnifying power in this case? Explain.
A constant power is supplied to a rotating disc. The relationship between the angular velocity $\omega$ of the disc and number of rotations (n) made by the disc is governed by
A parallel plate capacitor with air between the plates has a capacitance of 8 pF (1pF = 10–12 F). What will be the capacitance if the distance between the plates is reduced by half, and the space between them is filled with a substance of dielectric constant 6?
A Cassegrain telescope uses two mirrors as shown in Fig. 9.26. Such a telescope is built with the mirrors 20 mm apart. If the radius of curvature of the large mirror is 220 mm and the small mirror is 140 mm, where will the final image of an object at infinity be?
A Cassegrain telescope uses two mirrors
Fig. 9.26
A 60 μF capacitor is connected to a 110 V, 60 Hz ac supply. Determine the rms value of the current in the circuit
A circular coil of wire consisting of 100 turns, each of radius 8.0 cm carries a current of 0.40 A. What is the magnitude of the magnetic field B at the centre of the coil?

A small bulb is placed at the bottom of a tank containing water to a depth of 80cm. What is the area of the surface of water through which light from the bulb can emerge? The refractive index of water is 1.33. (Consider the bulb to be a point source.)

surface of water through which light from the bulb

In Young’s double-slit experiment using monochromatic light of wavelength \(λ\), the intensity of light at a point on the screen where path difference is \(λ\), is k units. What is the intensity of light at a point where path difference is \(\frac{λ }{3}\)?
A 3.0 cm wire carrying a current of 10 A is placed inside a solenoid perpendicular to its axis. The magnetic field inside the solenoid is given to be 0.27 T. What is the magnetic force on the wire?
The displacement of a body is given to be proportional to the cube of time elapsed. The magnitude of the acceleration of the body, is
A beam of light consisting of two wavelengths, 650 nm and 520 nm, is used to obtain interference fringes in a Young’s double-slit experiment.
(a) Find the distance of the third bright fringe on the screen from the central maximum for wavelength 650 nm.
(b) What is the least distance from the central maximum where the bright fringes due to both the wavelengths coincide?
In a Young’s double-slit experiment, the slits are separated by 0.28 mm and the screen is placed 1.4 m away. The distance between the central bright fringe and the fourth bright fringe is measured to be 1.2 cm. Determine the wavelength of light used in the experiment.
The photoelectric cut-off voltage in a certain experiment is 1.5 V. What is the maximum kinetic energy of photoelectrons emitted?
The work function of caesium metal is \(2.14 eV\). When light of frequency \(6×1014Hz\) is incident on the metal surface,photoemission of electrons occurs. What is the
(a)maximum kinetic energy of the emitted electrons, 
(b)Stopping potential, and
(c)maximum speed of the emitted photoelectrons?

Four point charges \(q_A\)\( = 2 µC\), \(q_B\) \(= −5 µC\), \(q_C\) = 2 µC, and \(q_D\) \(= −5 µC\) are located at the corners of a square ABCD of side 10 cm. What is the force on a charge of 1 µC placed at the centre of the square?

Figure 9.37 shows an equiconvex lens (of refractive index 1.50) in contact with a liquid layer on top of a plane mirror. A small needle with its tip on the principal axis is moved along the axis until its inverted image is found at the position of the needle.
an equiconvex lens in contact with a liquid layer on top of a plane mirror
Use Lenz’s law to determine the direction of induced current in the situations described by Fig. 6.16:
  1. A wire of irregular shape turning into a circular shape
  2. A circular loop being deformed into a narrow straight wire
the direction of induced current
A bar magnet of magnetic moment 1.5 J T-1 lies aligned with the direction of a uniform magnetic field of 0.22 T.
  1. What is the amount of work required by an external torque to turn the magnet so as to align its magnetic moment:
    (i) normal to the field direction,
    (ii) opposite to the field direction?
  2. What is the torque on the magnet in cases (i) and (ii) ?

Light incident normally on a plane mirror attached to a galvanometer coil retraces backwards as shown in Fig. 9.29. A current in the coil produces a deflection of 3.5o of the mirror. What is the displacement of the reflected spot of light on a screen placed 1.5 m away?

If the solenoid in Exercise 5.5 is free to turn about the vertical direction and a uniform horizontal magnetic field of 0.25 T is applied, what is the magnitude of torque on the solenoid when its axis makes an angle of 30° with the direction of applied field?