Science (English Medium) Class 12 - CBSE Question Bank Solutions for Physics

A soap film of thickness 0.0011 mm appears dark when seen by the reflected light of wavelength 580 nm. What is the index of refraction of the soap solution if it is known to be between 1.2 and 1.5?

Two concave lenses L₁ and L₂ are kept in contact with each other. If the space between the two lenses is filled with a material of smaller refractive index, the magnitude of the focal length of the combination

Two converging lenses of unequal focal lengths can be used to reduce the aperture of a parallel beam of light without loosing the energy of the light. This increase the intensity. Describe how the converging lenses should be placed to do this.

A convex lens forms a real image of a point object placed on its principals axis. If the upper half of the lens is painted black,
(a) the image will be shifted downward
(b) the image will be shifted upward
(c) the image will not be shifted
(d) the intensity of the image will decrease.

A small piece of wood is floating on the surface of a 2.5 m deep lake. Where does the shadow form on the bottom when the sum is just setting? Refractive index of water = 4/3.

A pin of length 2.0 cm lies along the principal axis of a converging lens, the centre being at a distance of 11 cm from the lens. The focal length of the lens is 6 cm. Find the size of the image.

A long, straight wire carries a current i. The magnetising field intensity H is measured at a point P close to the wire. A long, cylindrical iron rod is brought close to the wire, so that the point P is at the centre of the rod. The value of H at P will ______________ .

Which of the following pairs has quantities of the same dimensions?
(a) Magnetic field B and magnetising field intensity H
(b) Magnetic field B and intensity of magnetisation I
(c) Magnetising field intensity H and intensity of magnetisation I
(d) Longitudinal strain and magnetic susceptibility

Mark out the correct options.
(a) Diamagnetism occurs in all materials.
(b) Diamagnetism results from the partial alignment of permanent magnetic moment.
(c) The magnetising field intensity, H, is always zero in free space.
(d) The magnetic field of induced magnetic moment is opposite the applied field.

The magnetic intensity H at the centre of a long solenoid carrying a current of 2.0 A, is found to be 1500 A m⁻¹. Find the number of turns per centimetre of the solenoid.

The magnetic field inside a long solenoid of 50 turns cm⁻¹ is increased from 2.5 × 10⁻³ T to 2.5 T when an iron core of cross-sectional area 4 cm² is inserted into it. Find (a) the current in the solenoid (b) the magnetisation I of the core and (c) the pole strength developed in the core.

The magnetic field B and the magnetic intensity H in a material are found to be 1.6 T and 1000 A m⁻¹, respectively. Calculate the relative permeability µ_r and the susceptibility χ of the material.

Assume that each iron atom has a permanent magnetic moment equal to 2 Bohr magnetons (1 Bohr magneton equals 9.27 × 10⁻²⁴ A m²). The density of atoms in iron is 8.52 × 10²⁸ atoms m⁻³. (a) Find the maximum magnetisation I in a long cylinder of iron (b) Find the maximum magnetic field B on the axis inside the cylinder.

The magnetic field energy in an inductor changes from maximum to minimum value in 5.0 ms when connected to an AC source. The frequency of the source is

An inductor, a resistance and a capacitor are joined in series with an AC source. As the frequency of the source is slightly increased from a very low value, the reactance

An inductor coil of some resistance is connected to an AC source. Which of the following quantities have zero average value over a cycle?
(a) Current
(b) Induced emf in the inductor
(c) Joule heat
(d) Magnetic energy stored in  the inductor

The photocurrent in an experiment on photoelectric effect increases if ______.

An inductance of 2.0 H, a capacitance of 18μF and a resistance of 10 kΩ is connected to an AC source of 20 V with adjustable frequency.
(a) What frequency should be chosen to maximize the current in the circuit?
(b) What is the value of this maximum current?

An inductor-coil, a capacitor and an AC source of rms voltage 24 V are connected in series. When the frequency of the source is varied, a maximum rms current of 6.0 A is observed. If this inductor coil is connected to a battery of emf 12 V and internal resistance 4.0 Ω, what will be the current?

Balmer series was observed and analysed before the other series. Can you suggest a reason for such an order?