Physics Unsolved Sample Paper Solutions ISC Class 12
(B) (i) Magnetic induction due to an infinitely long straight wire =µ0I/2πa ...(i)
Magnetic induction due to the circular coil carrying current at its centre=µ0nI/2a ...(ii)
Dividing equations (i) and (ii)
(ii) Magnetic induction due to circular coil carrying current at its centre = µ0nI/2a ...(i)
According to question,
Magnetic induction due to circular coil = Magnetic induction due to the arc
(iii) In a n-type semiconductor, electrons are majority charge carriers and holes are minority charge carriers.
(iv) Reverse biased p-n junction has more resistance.
(vi) If the source of light is linear, then the wavefront is cylindrical where square of the amplitude is inversely proportional to the distance. If the source of light is a point source, then the wavefront is spherical where the amplitude is inversely proportional to the distance. The plane wavefront is appeared at infinite distance from the source and the rays are always parallel straight lines.
(vii) Yes the rays which appear to diverge from the virtual image are real. Hence, they can be focussed on the screen of the camera to form a real image.
(i) In self-pollinated species the seeds are not formed because of self-incompatibility where there is no growth of pollen tube on the stigma of a flower that prevents the fusion of gametes and thereby developing into an embryo. Hence, in such species seed could not be formed.
|S.No.||Drift velocity||Thermal velocity|
|(a)||When a potential difference is applied across a metal, the free electrons drift with a small constant velocity in the direction opposite to the applied field is called drift velocity.||The conduction electrons move in all directions with all possible velocities called thermal velocities.|
|(b)||Drift velocity is or the order or 10–6 m/s. It is very small.||Thermal velocity is very large and is of the order of 106 m/s.|
|(c)||When the electric field is zero, drift velocity is also zero.||Electrons move with thermal velocity even in the absence as well as in the presence of electric field.|
(ii) Formation of energy bands in solids: An isolated atom has well defined energy levels. When large number of such atom get together to form a real soild, their individual energy levels overlap and get completely modified. Instead of discrete value of energy of electrons, the value lies in a certain range. The collection of these closely packed energy levels are said to form an energy band. Two type of such bands formed in solid are called valence band and conduction band. The band formed by filled energy levels is known as valence band, whereas partially filled or unfilled band is known as conduction band. The two bands are generally separated by a gap called energy gap or forbidden gap. Conductors : In case of conductors, electrons fill the conduction band, partially the overlapping of both the bands i.e., valence and conduction band also take place. This shows that no forbidden gap is present.
Insulators : In case of insulator, forbidden gap is very large (> 6 eV). On the other hand, its valence band is fully filled with the electrons, whereas its conduction band is empty.
Semiconductor : In case of semiconductors the conduction band is empty and valence band is filled with electrons. Like insulators, forbidden energy gap is not so large in case of semiconductors. The gap is very small. The energy gap is nearly of 1 eV.
(i) When the sun shines upon falling raindrops, an observer with his back towards the sun sees concentric arcs of spectral colours hanging in the sky. These coloured arcs, which have their common centre on the line joining the sun and the observer, are called ‘rainbow’. Usually, two rainbows are seen, one above the other.
The lower one is called the ‘primary’ rainbow and the higher one is called the ‘secondary’ rainbow. The primary rainbow is brighter and narrower, having its inner edge violet and the outer edge red. The secondary rainbow, which is comparatively fainter, has reverse order of colours.
Let e, m, v be the charge, mass and velocity of the electron and r be the radius of the orbit. Positive charge on the nucleus is Ze. In case of hydrogen atom, Z = 1. Centripetal force is provided by electrostatic force of attraction. Therefore,
(i) Light emitting diode (LED)
(ii) Semiconductor : In case of semiconductors, the conduction band is empty and valence band is filled with electrons. Like insulators, forbidden energy gap is not so large in case of semiconductors. The gap is very small. The energy gap is nearly of 1 eV.
(iii) The diffusion of electrons from n-region to the p-region of the diode causes depletion region in a p-n junction.
(a) There are two important radioactive decay laws :
(b) Let at time t = 0, the number of radioactive atoms present be N0 and at time t, the number be N. Let dN atoms disintegrate in a time dt.
According to Rutherford and Soddy law, we have :
(a) Transitions labelled A shows absorption lines of Lyman series.
(b) Transitions labelled B show emission lines of Balmer series.
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