Physics - 2007
(Set I - Delhi)
General Instructions:
- All questions are compulsory.
- There is no overall choice. However, an internal choice has been provided in one question of two marks, one question of three marks and all three questions of five marks. You have to attempt only one of the choice in such questions.
- Question numbers 1 to 5 are very short answer type questions, carrying one mark each.
- Question numbers 6 to 12 are short answer type questions, carrying two marks each.
- Question numbers 13 to 24 are also short answer type questions, carrying three marks each.
- Questions numbers 25 to 27 are long answer type questions, carrying five marks
each.
Q. 1. An electron, an alpha-particle and a proton have the same kinetic energy. Which one of these particles has the largest de-Broglie wavelength ? 1
Q. 2. Why should the material used for making permanent magnets have high coercivity? 1
Q. 3. The radioactive isotope D decays according to the sequence
If the mass number and atomic number of D2 are 176 and 71 respectively, what is (i) the mass number (ii) atomic number of D ? 1
Q. 4. What will be the values of input A and B for the Boolean expression? 1
Q. 5. Why is frequency modulation perferred over amplitude modulation for transmission of music? 1
Q. 6. The output of an OR gate is connected to both the inputs of a NAND gate. Draw the logic circuit of this combination of getes and write its truth table. 2
Q. 7. Draw a plot of potential energy of a pair of nucleons as a function of their separation. What is the significance of negative potential energy in the graph drawn ? 2
Q. 8. A convex lens of refractive index 1.5 has a focal length of 18 cm in air. Calculate the change in its focal length when it is immersed in water of refractive index . 2
Q. 9. Distinguish between the terms 'average value' and 'rms value' of an alternating current. The instantaneous current from an a.c. source is I = 5 sin (314 t) ampere. What are the average and rms values of the current ? 2
Q. 10. Write the relation for the forece acting on a charge carrier q moving with a velocity through a magnetic field in vector notation. Using this relation, deduce the conditions under which this force will be (i) maximum (ii) minimum. 2
Q. 11. A cylindrical metallic wire is stretched to increase its length by 5%. Calculate the percentage change in its resistance. 2
Q. 12. The electric field E due to a point charge at any point near it is defined as where q is the test charge and F is the force acting on it. What is the physical significance of in this expression ? Draw the electric field lines of a point charge Q when (i) Q > 0 and (ii) Q < 0. 2
Or
Define electric flux. Write its S.I. units. A spherical rubber balloon carries a charge that is uniformly distributed over its surface. As the balloon is blown up and increases in size, how does the total electric flux coming out of the surface change ? Give reason.
Q. 13. Deduce an expression for the electric potential due to an electric dipole at any point on its axis. Mention one contrasting feature of electric potential of a dipole at a point as compared to that due to a single charge. 3
Q. 14. A parallel plate capacitor, each with plate area A and separation d, is charged to a potential difference V. The battery used to charge it is then disconnected. A dielectric slab of thickness d and dielectric constant K is now placed between the plates. What change, if any, will take place in
- charge on the plates
- electric field intensity between the plates
- capacitance of the capacitor.
Justify your answer in each case. 3
Q. 15. State Kirchhoff's rules of current distribution in an electrical network.
Using these rules determine the value of the current in the electric circuit given below. 3
Q. 16. Write the mathematical relation for the resistivity of a material in terms of relaxation time, number density and mass and charge of charge carriers in it. Explain, using this relation, why the resistivity of a metal increases and that of a semi-conductor decreases with rise in temperature. 3
Q. 17. Explain with the help of a labelled diagram the underlying principle and working of a step-up transformer. Why cannot such a device be used to step-up d.c. voltage ? 3
Or
Draw a labelled diagram of an a.c. generator. Explain briefly its principle and working. 3
Q. 18. Given below are two electric circuits A and B
Calculate the ratio of power factor of the circuit B to the power factor of circuit A. 3
Q. 19. Define the term 'resolving power' of an astronomical telescope. How does it get affected on
- increasing the aperture of the objective lens ?
- increasing the wavelength of the light used ?
Justify your answer in each case. 3
Q. 20. Write any four characteristics of electromagnetic waves. Give two uses each of
- Radio-waves
- Micro-waves. 3
Q. 21. In a plot of photoelectric current versus anode potential, how does
- the saturation current vary with anode potential for incident radiations of different frequencies but same intensity ?
- the stopping potential vary for incident radiations of different intensities but same frequency ?
- photoelectric current vary for different intensities but same frequency of incident radiations ?
Justify your answer in each case. 3
Q. 22. Calculate the amount of energy released during the a-decay of
Given : 1. atomic mass of
2. atomic mass of
3. atomic mass of
Is this decay spontaneous ? Give reason. 3
Q. 23. What is a digital signal ? Explain the function of modem in data communication. Write two advantages of digital communication. 3
Q. 24. Explain, with the help of a schematic diagram, the principle and working of a Light Emitting Diode. What criterion is kept in mind while choosing the semiconductor material for such a device ? Write any two advantages of Light Emitting Diode over conventional incandescent lamps. 3
Q. 25. Draw a labelled diagram of a moving coil galvanometer. State the principle on which it works. Deduce an expression for the torque acting on a rectangular current carrying loop kept in a uniform magnetic field. Write two factors on which the current sensitivity> of a moving coil galvanometer depend. 5
Or
State Biot-Savart law. Use it to derive an expression for the magnetic field at the centre of a circular loop of radius R carrying a steady current I. Sketch the magnetic field lines for such a current carrying loop. 5
Q. 26. What are coherent sources ? Why are coherent sources required to produce interference of light ? Give an example of interference of light in everyday life. In Young's double slit experiment, the two slits are 0.03 cm apart and the screen is placed at a distance of 1.5 m away from the slits. The distance between the central bright fringe and fourth bright fringe is 1 cm. Calculate the wavelength of light used. 5
Or
State the condition under which the phenomenon of diffraction of light takes place. Derive an expression for the width of the central maximum due to diffraction of light at a single slit. A slit of width 'a' is illuminated by a monochromatic light of wavelength 700 nm at normal incidence. Calculate the value of 'a' for position of
- first minimum at an angle of diffraction of 30°.
- first maximum at an angle of diffraction of 30°. 5
Q. 27. State the principle of working of p-n diode as a rectifier. Explain, with the help of a circuit diagram, the use of p-n diode as a full wave rectifier. Draw a sketch of the input and output waveforms. 5
Or
Draw the symbolic representation of a (i) p-n-p, (ii) n-p-n transistor. Why is the base region of transistor thin and lightly doped ? With proper circuit diagram, show the biasing of a p-n-p transistor in co mmon base configuration. Explain the movement of charge carriers through different parts of the transistor in such a configuration and show that . 5
Physics - 2007
(Set II - Delhi)
General Instructions:
- All questions are compulsory.
- There is no overall choice. However, an internal choice has been provided in one question of two marks, one question of three marks and all three questions of five marks. You have to attempt only one of the choice in such questions.
- Question numbers 1 to 5 are very short answer type questions, carrying one mark each.
- Question numbers 6 to 12 are short answer type questions, carrying two marks each.
- Question numbers 13 to 24 are also short answer type questions, carrying three marks each.
- Questions numbers 25 to 27 are long answer type questions, carrying five marks
each.
Q. 1. In a series LCR circuit, the voltages across an inductor, a capacitor and a resistor are 30 V, 30 V and 60 V respectively. What is the phase difference between the applied voltage and the current in the circuit ? 1
Q. 2. Ultraviolet radiations of different frequencies and are incident on two photosensitive materials having work functions and respectively. The kinetic energy of the emitted electrons is same in both the cases. Which one of the two radiations will be of higher frequency ? 1
Q. 3. Define the term 'activity' of radionuclide. Write its SI unit. 1
Q. 4. An electron is moving a along +ve x-axis in the presence of uniform magnetic field along +ve y-axis. What is the direction of the force acting on it ? 1
Q. 5. What should be the length of dipole antenna for a carrier wave of frequency ? 1
Q. 6. Two point charges and are separated by a distance of 1 m in air. Calculate at what point on the line joining the two charges is the electric potential zero. 2
Q. 7. A voltage of 30 V is applied across a carbon resistor with first, second and third rings of blue, black and yellow colours respectively. Calculate the value of current, in mA, through the resistor. 2
Q. 8. A galvanometer has a resistance of It gives full scale deflection with a current of 2 mA. Calculate the value of the resistance needed to convert it into an ammeter of range 0-0.3 A. 2
Q. 9. Calculate the current drawn by the primary of a transformer which steps down 200 V to 20 V to operate a device of resistance . Assume the efficiency of the transformer to be 80%. 2
Or
An a.c. voltage of 100 V, 50 Hz is connected across a 20 ohm resistor and mH inductor in series. Calculate (i) impedance of the circuit, (ii) rms current in the circuit.
Q. 10. Define resolving power of a compound microscope. How does the resolving power of a
compound microscope change when
(i) refractive index of the medium between the object and objective lens increases ?
(ii) wavelength of the radiation used is increased ? 2
Q. 11. Draw a graph showing the variation of potential energy between a pair of nucleons as a function of their separation. Indicate the regions in which the nuclear force is
- attractive,
- repulsive. 2
Q. 12. Two semiconductor materials X and Y shown in the given figure, are made by doping germanium crystal with indum and arsenic respectively. The two are joined end to end and connected to a battery as shown.
- Will the junction be forward biased or reverse biased ?
- Sketch a V-I graph for this arrangement. 2
Q. 13. State Gauss's theorem in electrostatics. Apply this theorem to derive an expression for electric field intensity at a point near an infinitely long straight charged wire. 3
Q. 14. Explain the underlying principle of working of a parallel plate capacitor.
If two similar plates, each of area A having surface charge densities and are separated by a distance d in air, write expressions for
- the electric field at points between the two plates.
- the potnetial difference between the plates.
- the capacitance of the capacitor so formed. 3
Q. 15. For the potentiometer circuit shown in the given figure, points X and Y reprensent the two terminals of an unknown emf E'. A student observed that when the jockey in moved from the end A to the end B of the potentiometer wire, the deflection in the galvanometer remains in the same direction.
What may be the two possible faults in the circuit that could result in this obsevation ?
If the galvanometer deflection at the end B is (i) more, (ii) less, than that at the end A, which of the two faults, listed above, would be there in the circuit ?
Give reasons in support of your answer in each case. 3
Or
The given figure shows a network of resistances R1, R2, R3 and R4.
Using Kirchhoff's laws, establish the balance condition for the network.
Q. 16. What is Seebeck effect ? Plot a graph showing the variation of thermo emf with temperature of hot junction (keeping cold junction at 0°C) of a thermocouple. How will the (i) neutral temperature, (ii) inversion temperature of a thermocouple change when the temperature of cold junction is increased ? 3
Q. 17. Name the following constituent radiations of electromagnetic spectrum which
- produce intense heating effect.
- is absorbed by the ozone layer in the atmosphere.
- is used for studying crystal structure.
Write one more application forr each of these radiations. 3
Q. 18. A double convex lens of glass of refractive index 1.6 has its both surfaces of equal radii of curvature of 30 cm each. An object of height 5 cm is placed at a distance of 12.5 cm from the lens. Calculate the size of the image formed. 3
Q. 19. Draw a schematic diagram of the experimental arrangement used by Davisson and Germer to establish the wave nature of electrons. Explain briefly how the de-Broglie relation was experimentally verified in case of electrons. 3
Q. 20. Draw the graph to show variation of binding energy per nucleon with mass number of different atomic nuclei. Calculate binding energy/nucleon of nucleus. 3
Given :
mass of
mass of proton = 1.007825 u
mass of neutron = 1.008665 u
and 1 u = 931 MeV/C2
Q. 21. Draw the circuit diagram of a common emitter amplifier using n-p-n transistor. What is the phase differnece between the input signal and output voltage ? State two reasons why a common emitter amplifier is preferred to a common base amplifier. 3
Q. 22. Explain the formation of energy band in solids. Draw energy band diagram for (i) a conductor, (ii) an intrinsic semiconductor. 3
Q. 23. What is modulation ? Explain the need of modulating a low frequency information signal. With the help of diagrams, differentiate between PAM and PDM. 3
Q. 24. Write the acronym LASER in expanded form. State any four reasons for preferring diode lasers as light sources for optical communication links. 3
Q. 25. Explain, with the help of a labelled diagram, the principle and construction of a cyclotron.
Deduce an expression for the cyclotron frequency and show that it does not depend on the speed of the charged particle. 5
Or
Distinguish the magnetic properties of dia, para- and ferro-magnetic substances in terms of (i) susceptibility, (ii) magnetic permeability and (iii) coercivity. Give one example of each of these materials.
Draw the field lines due to an external magnetic field near a (i) diamagnetic,
(ii) paramagnetic substance.
Q. 26. Explain the term 'inductive reactance'. Show graphically the variation of inductive reactance with frequency of the applied alternating voltage.
An a.c. voltage is applied across a pure inductor of inductance L. Show mathematically that the current flowing through it lags behind the applied voltage by aphase angle of . 5
Or
Explain the term 'capacitive reactance'. Show graphically the variation of capacitive reactance with frequency of the applied alternating voltage.
An a.c. voltage is applied across a pure capacitor of capacitance C. Show mathematically that the current flowing through it leads the applied voltage by a phase angle of .
Q. 27. State the essential condition for diffraction of light to take place.
Use Huygen's principle to explain diffraction of light due to a narrow single slit and the formation of a patern of fringes obtained on the screen. Sketch the pattern of fringes formed due to diffraction at a single slit showing variation of intensity with angle . 5
Or
What are coherent sources of light ? Why are coherent sources required to obtain sustained interference pattern ?
State three characteristic features which distinguish the interference pattern due to two coherently illuminated sources as compared to that observed in a diffraction pattern due to a single slit.
Physics - 2007
(Set III - Delhi)
General Instructions:
- All questions are compulsory.
- There is no overall choice. However, an internal choice has been provided in one question of two marks, one question of three marks and all three questions of five marks. You have to attempt only one of the choice in such questions.
- Question numbers 1 to 5 are very short answer type questions, carrying one mark each.
- Question numbers 6 to 12 are short answer type questions, carrying two marks each.
- Question numbers 13 to 24 are also short answer type questions, carrying three marks each.
- Questions numbers 25 to 27 are long answer type questions, carrying five marks
each.
Q. 1. Is the force acting between two point electric charges q1 and q2 kept at some distance apart in air, attractive or repulsive when (i) q1q2 > 0 (ii) q1q2 > 0 ? 1
Q. 2. Show graphically how the stopping potential for a given photosensitive surface varies with the frequency of incident radiations. 1
Q. 3. A TV tower has a height of 71 m. What is the maximum distance upto which TV transmission can be received ? Given that the radius of the earth = 6.4 × 106 m. 1
Q. 4. Which one of the two diodes D1 and D2 in the given figures is (i) forward biased, (ii) reverse biased ? 1
Q. 5. Suggest a possible communication channel for the transmission of a message signal which has a bandwidth of 5 MHz. 1
Q. 6. A spherical Gaussian surface encloses a charge of .
- Calculate the electric flux passing through the surface.
- How would the flux change if the radius of the Gaussian surface is doubled and why ? 2
Q. 7. In a copper voltameter, the mass of the ions deposited in 30 seconds is m grams. The current (i) vs. time (t) graph for the experiment is as shown in the given figure.
Calculate the value of E.C.E. of copper in terms of the mass, m, deposited. 2
Or
For a given thermocouple, the emf generated across its ends is given by E = at + bt2 where t in °C is the temperature of the hot junction, the cold junction being at 0 °C. If V/°C2, calculate the value of inversion temperaturemV /°C and b = -0.02 ma = 10 in °C.
Q. 8. In an ammeter (consisting of a galvanometer and a shunt), 0.5% of the main current passes through the galvanometer. Resistance of the galvanometer coil is G. Calculate the resistance of the shunt in terms of galvanometer resistance, G. 2
Q. 9. An electric bulb B and a parallel plate capacitor C are connected in series to the a.c. mains as shown in the given figure. The bulb glows with some brightness. How will the glow of the bulb be affected on introducing a dielectric slab between the plates of the capacitor ? Give reasons in support of your answer. 2
Q. 10. What does the statement, “natural light emitted from the sun is unpolarized” mean in terms of the direction of electric vector ? Explain briefly how plane polarized light can be produced by reflection at the interface separating the two media. 2
Q. 11. The output of a 2-input NOR gate is fed to a NOT gate. Draw the logic circuit of this combination of gates and write the truth table for the output of the combination for all inputs. (i) attractive, (ii) repulsive. 2
Q. 12. What is remote sensing ? Write its two applications. 2
Q. 13. On what principle does a metre bridge work ? Draw a circuit diagram and explain how this device can be used for determination of an unknown resistance. 3
Q. 14. Derive a mathematical expression for resistivity of a conductor in terms of number density of charge carries in the conductor and relaxation time. 3
Q. 15. State Ampere’s circuital law. Write the expression for the magnetic field at the centre of a circular coil of radius R carrying a current I. Draw the magnetic field lines due to this coil. 3
Q. 16. Write the expression for the force acting on a charged particle of charge q moving with velocity in the presence of magnetic field . Show that in the presence of this force
- the kinetic energy of the particle does not change.
- its instantaneous power is zero. 3
Q. 17. In a series LCR circuit, define the quality factor (Q) at resonance. Illustrate its significance by giving one example.
Show that power dissipated at resonance in LCR circuit is maximum. 3
Q. 18. rad/s about an axis pA circular copper disc 10 cm in radius rotates at a speed of 20 through its centre and perpendicular to the disc. A uniform magnetic field of 0.2 T acts perpendicular to the disc.
- Calculate the potential difference developed between the axis of the disc and the rim.
- What is the induced current if the resistance of the disc is ? 3
Or
F are connected in series to 220 V a.c.mA resistor of and a capacitor of 40 source with angular frequency . Calculate the voltages (rms) across the resistor and the capacitor. Why is the algebraic sum of these voltages more than the source voltage ? How do you resolve this paradox ?
Q. 19. Draw a labelled diagram of Hertz’s experiment. Explain how electromagnetic radiations are produced using this set-up. 3
Q. 20. How does the frequency of a beam of ultraviolet light get affected when it goes from air into glass ?
A ray of light incident on an equilateral glass prism shows minimum deviation of 30°.
Calculate the speed of light through the glass prism. 3
Q. 21. An electron, a-particle and a proton have the same de-Broglie wavelength. Which of these particles has (i) minimum kinetic energy, (ii) maximum kinetic energy, and why ? In what way has the wave nature of electron been exploited in electron microscope ? 3
Q. 22. State the law of radioactive decay. Establish a mathematical relation between half-life period and disintegration constant of a radioactive nucleus. 3
Q. 23. Distinguish between nuclear fission and fusion. In a fusion reaction calculate the amount of energy (in MeV) released. Given. 3
Q. 24. Draw a schematic diagram of a single optical fibre structure. On what principle does such a device work ? Explain the mechanism of propagation of light signal through an optical fibre. 3
Q. 25. Derive the expression for the energy stored in a parallel plate capacitor of capacitance C with air as medium between its plates having charges Q and — Q. Show that this energy can be expressed in terms of electric field as where A is the area of each plate and d is the separation between the plates.
How will the energy stored in a fully charged capacitor change when the separation between the plates is doubled and a dielectric medium of dielectric constant 4 is introduced between the plates ? 5
Or
Define the term dipole moment of an electric dipole indicating its direction. Write its SI unit.
An electric dipole is placed in a uniform electric field . Deduce the expression for the torque acting on it. In a particular situation, it has its dipole moment aligned with the electric field. Is the equilibrium stable or unstable ?
Q. 26. Define the term ‘wavefront’. Draw the wavefront and corresponding rays in the case of a
(i) diverging spherical wave, (ii) plane wave.
Using Huygen’s construction of a wavefront, explain the refraction of a plane wavefront at a plane surface and hence verify Snell’s law. 5
Or
Derive the relation between the focal length of a convex lens in terms of the radii of curvature of the two surfaces and refractive index of its material. Write the sign conventions and two assumptions used in the derivation of this relation,
A convex lens of focal length 40 cm and a concave lens of focal length — 25 cm are kept in contact with each other. What is the value of power of this combination ?
Q. 27. Explain, with the help of a circuit diagram, the use of an n-p-n transistor as an amplifier in common-emitter configuration. Write the expression for voltage gain of the transistor. Draw frequency response curve of this amplifier.
How will the current gain of a transistor be affected if its base region is made thicker as compared to a usual transistor and why ? 5
Or
Draw energy band diagrams for (i) an intrinsic semiconductor, (ii) p-type semiconductor.
Draw symbolic representation of a zener diode. Draw its V-I characteristics and explain, with the help of a circuit diagram, its use as a voltage regulator.
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