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

The currents flowing in the two coils of self-inductance L₁ = 16 mH and L₂ = 12 mH are increasing at the same rate. If the power supplied to the two coil is equal, find the ratio of the energies stored in the two coils at a given instant ?

Which of the following substances are diamagnetic?

Bi, Al, Na, Cu, Ca and Ni

Which of the following substances are para-magnetic?

Bi, Al, Cu, Ca, Pb, Ni

 In a nuclear reaction

`"_2^3He + _2^3He -> _2^4He +_1^1H +_1^1H + 12.86 Me V` though the number of nucleons is conserved on both sides of the reaction, yet the energy is released. How? Explain.

The susceptibility of a magnetic material is − 2.6 × 10⁻⁵. Identify the type of magnetic material and state its two properties.

Define self-inductance of a coil. Show that magnetic energy required to build up the current I in a coil of self inductance L is given by `1/2 LI^2`

A rectangular loop of wire of size 4 cm × 10 cm carries a steady current of 2 A. A straight long wire carrying 5 A current is kept near the loop as shown. If the loop and the wire are coplanar, find

(i) the torque acting on the loop and

(ii) the magnitude and direction of the force on the loop due to the current carrying wire.

Using Bohr’s second postulate of quantization of orbital angular momentum show that the circumference of the electron in the n^th orbital state in hydrogen atom is n times the de Broglie wavelength associated with it.

Derive the expression for the self-inductance of a long solenoid of cross sectional area A and length l, having n turns per unit length.

A rectangular loop of wire of size 2 cm × 5 cm carries a steady current of 1 A. A straight long wire carrying 4 A current is kept near the loop as shown. If the loop and the wire are coplanar, find (i) the torque acting on the loop and (ii) the magnitude and direction of the force on the loop due to the current carrying wire.

The relative magnetic permeability of a magnetic material is 800. Identify the nature of magnetic material and state its two properties.

A rectangular loop of wire of size 2.5 cm × 4 cm carries a steady current of 1 A. A straight wire carrying 2 A current is kept near the loop as shown. If the loop and the wire are coplanar, find the (i) torque acting on the loop and (ii) the magnitude and direction of the force on the loop due to the current carrying wire.

Mention the two characteristic properties of the material suitable for making core of a transformer.

State the underlying principle of a transformer. How is the large scale transmission of electric energy over long distances done with the use of transformers?

A rectangular loop of size l × b carrying a steady current I is placed in a uniform magnetic field `vecB`. Prove that the torque  `vectau`acting on the loop is give by `vectau =vecm xx vecB,`where `vecm` is the magnetic moment of the loop.

A capacitor of 200 pF is charged by a 300 V battery. The battery is then disconnected and the charge capacitor is connected to another uncharged capacitor of 100 pF. Calculate the difference between the final energy stored in the combined system and the initial energy stored in the single capacitor.

State the principle of a step-up transformer. Explain, with the help of a labeled diagram, its working ?

Describe briefly and two energy losses, giving the reasons for their occurrence in actual transformers ?

A magnetised needle of magnetic moment 4.8 × 10⁻² JT⁻¹ is placed at 30° with the direction of uniform magnetic field of magnitude 3 × 10⁻² T. Calculate the torque acting on the needle.

State the principle of working of a transformer. Can a transformer be used to step up or step down a d.c. voltage? Justify your answer.