Class-12, Subject-Physics SHORT ANsWER TYPE qUESTIONS
Q.1 State and prove Gauss's law.
Q.2 (1)An electron fals through a distance of 1.5 cm in a uniform electric field of magnitude 2.0x10* N/C. Calculate the time it takes to fal through this distance starting from rest.
(2) If the direction of the field is reversed keeping its magnitude unchanged, calculate the time taken by a proton to fall through this distance starting from rest.
Q.3 Using Guess's law, derive expression for the electric field intensity due to an infinitely long, straight wire of linear charge densitya C/m.
Q4 Define an equipotential surface? Write any two properties of an equipotential surface.
Q.5 What is a capacitor? Deduce an expresslon for the capacitance of a parallel plate capacitor with air as the medium between the plates.
Q.6 Deduce the relation between currentI flowing through a conductor and drift velocity of free electrons.
Q.7 Derive an expression for drift velocity of free electrons in a conductor in terms of relaxation time of electrons.
Q.8 State Ampere's circuital law.
Q.9 A proton and an Alfa-particle move perpendicular to a magnetic field. Find the ratio of radii of the circular paths described by them when both(1) have equal velocities and (2) equal kinetic energies.
Q.10 A proton and an Alfa-particle move perpendicular to a magnetic field. Find the ratio of radii of the circular paths described by them when both (1) have equal momentum (2) were accelerated through the same potential difference.
Q.11 State Biot -Savart's law and express this law in the vector form.
Q.12 Using Biot-Savart's law, deduce the expressionfor the magnetic field at a point (x) on the axis of a circular current carrying loop of radius R. Howis the direction of the magnetic field determined at this point?
Q.13 Derive with the help of figure, the expression for the magnetic field inside a very long solenoid having n turns per unit length carrying a current l.
Q.14(1) State the underlying principle of a moving coil galvanometer.
( ) Give two reasons to explain why a galvanometer can not as such be used to measure the value of the current in a given circuit.
i) Define the terms: (a) voltage sensitivity and (b) current sensitivity of a galvanometer.
Q.15 How is a galvanometer converted into a voltmeter and a ammeter? Draw the relevant diagrams and find the resistance of the arrangement in each case. Take resistance of galvanometer as G.
Q.16 Write two properties of a material suitable for making (i)a permanent magnet, and (i) an electromagnet.
Q.17 Write three points of difference between paramagnetic, diamagnetic and ferromagnetic materials, giving one example for each.
Q.18 Draw the magnetic field lines distinguishing between Diamagnetic and Paramagnetic materials. Give a simple explanation to account for the difference in the magnetic behaviour of these materials. Q.19 (1) Define the term 'self- inductance' and write its S.I uni
) Obtain the expression for the mutual inductance of two long coaxial solenoids S1and S2 wound one over the, each oflength Land radi r1 and r2 and n1 and n2 number of turns per unit length, when a current lis set up in the outer solenoid $2.
Q.20 A Lamp is connected in series with an indicator and an AC source. What happens to the brightness of the lamp when the key is plugged in and an iron rod is inserted inside the indicator? Explain. Q.21 In a series LR circuit XL =R and power factor of the circuit is P1. When capacitor with capacitance C such that XL=XC is put in series, the power factor becomes P2.Calculate P1/P2. Q.22 A resistance R and a capacitor C are connected in series to a source V= Vosinwt. Find:
(1) the peak value of thee voltage across the (a) resistance and (b) capacitor. (11) the phase difference between the applied voltage and current. What of them is ahead?
Q.23 A voltage V = Vosinwt is applied to a series LCR circuit. Derive an expression for average power dissipated over a cycle. Under what condition Is:(1) no power is dissipated even though the current flows through the circuit?(1i) maximum power dissipated in the circuit?
Q.24 How are electromagnetic waves produced? What is the source of energy of these waves?
Q.25 Draw a sketch of linearly polarized EM waves propagating in the Z-direction. Indicate the directions of the oscillating electric and magnetic fields. Q.26 State, with the help of a ray diagram the working principle of optical fibres. Write one important use of optical fibres. Q.27 Calculate the radius of curvature of an equi-concave lens of refractive index 1.5, when it is kept in a medium of refractive index 1.4, to have a please of-5D?
Q.28 An object is placed at (1) 10 c.m, (1) 5 c.m in front of a concave mirror of radius of curvature 15 cm. Find the position, nature, and magnification of the image in each case.
Q,29 Draw a ray diagram to show the refraction of light through a glass prism. Hence derive the relation.
Q.30 (i) Draw a ray diagram showing the formation of image by a reflecting telescope.
(in) Write two advantages of a reflecting telescope over a refracting telescope.
Q.31 (a) Draw a ray diagram of compound microscope for the final image formed at least distance of distinct vision?
(b) An angular magnification of 30X is desired using an objective of focal length 1.25 cm and an eye piece of focal length 5 cm. How will you set up the compound microscope for the final image formed at least distance of vision? Q.32 Draw a ray diagram of Astronomical Telescope for the final image formed at infinity.
(b) A small telescope has an objective lens of focal length 140 cm and an eyepiece of focal length 5.0 cm. Find the magnifying power of the telescope for viewing distant objects when (i) the telescope is in normal adjustment (ii) the final image is formed at the least distance of distinct vision.
Q.33 In Young's double slit experiment using monochromatic light of wavelength ,the intensity at a point on the screen where path difference is ,is K units. What is the intensity of ight at a point where path
difference is¥3? Q.34 Find the intensity at a point on a screen In Young's double slit experiment where the interfering waves of equal intensity have a path difference of (1)/4 (11)/3.
Q.35 Define the term wavefront. Using Huygens' wave theory, verify the laws of reflection.
Q.36 Deflne the term," refractlve Index" of a medlum. Verify Snell's law of refractlon when a
plane wavefront Is propagating from a denser to a rarer medlum.
Q.37 (1)If one of two ldentical slits producing Interference In Young's experiment ls covered with glass, so that the light Intensity passing through it is reduced to 50%,find the ratio of the maximum Intensity of the fringe In the Interference pattern.(1)What kind of fringes do you expect to observe if white light ls used Instead of monochromatic light?
.38 Define the term() cut off frequency and (i) threshold wavelength In photoelectrlc emisslon.
a.39 Define the terms (a) threshold frequency and (b) stopping potential in photoelectric effect.
(1)Plot graph of photocurrent versus anode potential for a radlation of frequency and Intenslty.
Q.40 Write two maln observations of photoelectric effect experiment which could only be
explained by Einsteln's photoelectric equation.
Q.41 Monochromatic light of frequency 6.0x101Hz is produced by a laser.The paper emitted is
2.0x10*W.() What ls the energy of a photon In a light beam?(1) Estimate the number of photons emitted per second on an average by the source.
a.42 The work function of Caesium metal is 2.148V. When light of frequency 6.0x101Hz is Incldent on metal surface, photoemlssilon of electron occurs. What is the:() maximum kinetic energy of emltted electrons.(ui)stopplng potential (m)maximum speed of emitted photoelctrons.
a.43 Using Bohr's atomic model, derive an expression for the radius of nth orbit of revolving9
electron in a hydrogen atom.
Q.44 Using Bohr's atomic model, derive the expression for the velocity of electron revolving in
the nth orbit of hydrogen atom.
Q.45 State Bohr's quantization condition of angular momentum. Calculate the shortest wavelength of the Brackett serles and state to which part of the electromagnetic spectrum does it belong.
Q.46 State the postulates of Bohr's model of hydrogen atom.
Q.47 Compare the radii of two nuclei with mass numbers 1 and 27 respectively. abundances of Q.48 The three stable isotopes of neon Ne2°,Ne21 and Ne22 have respective and 21.99u 90.51%,0.27%and 9.22%. The atomic masses of the three isotopes are19.99u,20.99u
respectively. Obtaln the average atomic mass of neon.
Q.49 Define the term mass defect and State the properties of nuclear force?
Q.50 How long an electric lamp of 100W can be kept glowing by fusion of 2.0kg of deuterium?
fuslon reaction can be taken as :1H+1H-2He+ n+3.2 Mev.
Q.51 What is the nuclear fusion and fission ? State the necessary conditions for nuclear fusion to occur.
Q.52 Write two points of difference between intrinsic and extrinsic semiconductors. q.53 Explain the terms 'depletion layer' and 'potential barrier' in a p-n junction diode. How are the (i)hwidth of depletion layer and (1) value of potential barrier affected when the p-n junction is forward biased?
Q,54 Distinguish between n-type and p-type semiconductors on the basis of energy band diagram. Compare their conductivities at absolute zero temperature and at room temperature.
Q.55 Explain with the help of a circuit diagram, the working of p-n junction diode as half wave and full wave rectifier.
LONGANSWER TYPEQUESTIONS: Q.1 (i) An electric dipole is held in a uniform electric field. Using suitable diagram show that it does not undergo any translatory motion. Derive the expression for the torque acting on it.(ii) What would happen if the field in non- uniform? (ii) What would happen if the field in non-uniform? (ii) What would happen if the external electric field E is increasing (a) parallel to p vector and (b) anti-parallel to p vector? Q.2 Derive an expression for the electric field intensity at a point on the equatorial line of an electric dipole moment p vector and length 2a. What is the direction of this field?
Q3 (i) Find out the orientation of the dipole when it is in (a) stable equilibrium (b) unstable equilibrium.
(i)Define electrie flux. Is it a scalar or a vector quantity?
Q.4 Using Gauss's law, deduce the expression for electric field due to uniformly charged spherical conducting shell of radius R at a point (i) outside and (i) inside the shell.
Q.5 (i) Start the two Kirchhoffs laws. Explain briefly how these rules are justified?
(i1) The current is drawn from a cell of emf E and internal resistance r connected to the network of resistors each of resistance r as shown in the figure: Obtain the expression for: (a) The current draw from the cell and (b) The power consumed in the network.
Q.6 Derive an expression for the force per unit length between the two infinity long straight parallel current carrying conductors. Hence define S.l. unit of current.
Q7 () Draw the diagram of a device which is used to decrease high AC voltage into a low AC voltage and state its working principle. Write four sources of energy losses in this device. (i1) A small town with a demand of 1200 kW of electric power at 220 V is situated 20 km away from an electric plant generating power at 440 V. The resistance of two wires line carrying power is 0.5 ohm per km. The town gets the power from the line through a 4000-220V step-down transformer at a sub-station in the town. Estimate the line power loss in the form of heat.
Q.8 (i) Draw a labelled diagram of AC generator. Derive the expression for the instantaneous value of the emf induced in the coil. (ii) A circular coil of cross-sectional area 200 cm and 20 turns is rotated about the vertical diameter with angular speed of 50 rad/sec in a uniform magnetic field of magnitude 3.0x10-2 T. Calculate the maximum value of the current in the coil.
Q.9 Derive the mathematical relation between refractive indices ni and n2 of two radi and radius of curvature R for refraction at a convex spherical surface. Consider the object to be a point since lying on the principle axis in Rarer medium of refractive index n1 and a real image formed in the denser medium of refractive index n2. Hence, derive lens maker's formula.
Q.10(1) Under what conditions is the phenomenon of total internal reflection of light observed? Obtain the relation between the critical angle of incidence and the refracthve index of the medium.(i1) Three lenses of focal lengths +10cm,-10cm and +30cm are arranged coaxially as in the figure given below. Find the position ofthe final image formed by the combination. Q.11 (1) Drawa ray diagram to show the image formation by a combination of two thin convex lenses in contact. Obtaln the expression for the power of thls combination in terms of the focal lengths of the lenses. (i1) A ray oflight passing from alr through an equllateral glass prilsm undergoes minimum deviation when the angle of incidence is 3/4 of the angle of prism. Calculate there speed of light in the prism. Q.12 Describe Young's double slit experiment to produce interference pattern due to a monochromatic source of light. Deduce the expression for the fringe wic
Q.13 Distinguish between a conductor, an insulator and a semiconductor on the basis of energy band diagrams.
