Nuclei — Physics STD 12 Science — Question

X-rays are

(a) Stream of electrons

(b) Stream of positively charged particles

(c) Electromagnetic radiations of high frequency

(d) Stream of uncharged particles

A circular current loop of magnetic moment M is in an arbitrary orientation in an external magnetic field B. The work done to rotate the loop by 30° about an axis perpendicular to its plane is:

Plutonium decays with a half-life of 24000 years. If the plutonium is stored for 72000 years, then the fraction of plutonium that remains is

(a)

(b)

(c)

(d)

X – rays and γ -  rays of the same energies may be distinguished by

(a) Their velocity	(b) Their ionising power
(c) Their intensity	(d) Method of production

AB is a potentiometer wire of length 100 cm and its resistance is 10 ohms.  It is connected in series with a resistance R = 40 ohms and a battery of e.m.f. 2 V and negligible internal resistance.  If a source of unknown e.m.f. E is balanced by 40 cm length of the potentiometer wire, the value of E is

(a) 0.8 V

(b) 1.6 V

(c) 0.08 V

(d) 0.16 V

In the circuit here, the steady state voltage across capacitor C is a fraction of the battery e.m.f. The fraction is decided by

(a) R1 only

(b) R1 and R2 only

(c)  and   only

(d)  and

Assertio  :   In the phenomenon of mutual induction, self induction of each of the coils persists.

Reason   : Self induction arises when strength of current in same coil changes. In mutual induction, current is changing in both the individual coils.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If the assertion and reason both are false.

An energy of 24.6 eV is required to remove one of the electrons from a neutral helium atom. The energy (in eV) required to remove both the electrons from a neutral helium atom is

(a) 79.0

(b) 51.8

(c) 49.2

(d) 38.2

For a coil having L = 2mH, current flow through it is I = t²e^−t then the time at which emf become zero: -

Diffraction effects are easier to notice in the case of sound waves than in the case of light waves because

(a) Sound waves are longitudinal	(b) Sound is perceived by the ear
(c) Sound waves are mechanical waves	(d) Sound waves are of longer wavelength