Therithal - Important questions with answers: 12 th Std Class Physics

Thursday 31 March 2016

12 th Std Class Physics - Importance questions with Answer Key

12 th Std Class Physics - Importance questions with Answer Key

UNIT 1 Electrostatics

UNIT 2 Current Electricity

UNIT 3 Effects of Electric Current

UNIT 4 Electromagnetic Induction and Alternating Current

AC generator (Dynamo) - Single phase and AC generator (Alternator) - Three phase -- - Download - Key Answer
Eddy currents and Applications of Eddy current -- - Download - Key Answer
Transformer Principle - Efficiency of a transformer - Energy losses in a transformer -- - Download - Key Answer

UNIT 5 Electromagnetic Waves and Wave Optics

UNIT 6 : Atomic Physics

UNIT 7 : Dual Nature of Radiation and Matter and Relativity

UNIT 8 : Nuclear Physics 83

UNIT 9 : Semiconductor Devices and their Applications

UNIT 10 : Communication Systems

Most Important Questions with Answer Key

UNIT 1 Electrostatics

1. State Coulomb’s law in electrostatics and represent it in vector form.

2. What is permittivity and relative permittivity? How are they related?

3. Explain the principle of superposition.

4. Define electric field at a point. Give its unit and obtain an expression for the electric field at a point due to a point charge.

5. Write the properties of lines of forces.

6. What is an electric dipole? Define electric dipole moment?

7. Derive an expression for the torque acting on the electric dipole when placed in a uniform field.

8. What does an electric dipole experience when kept in a uniform electric field and non−uniform electric field?

9. Derive an expression for electric field due to an electric dipole (a) at a point on its axial line (b) at a point along the equatorial line.

10. Define electric potential at a point. Is it a scalar or a vector quantity? Obtain an expression for electric potential due to a point charge.

11. Distinguish between electric potential and potential difference.

12. What is an equipotential surface?

13. What is electrostatic potential energy of a system of two point charges?

Deduce an expression for it.

14. Derive an expression for electric potential due to an electric dipole.

15. Define electric flux. Give its unit.

16. State Gauss’s law. Applying this, calculate electric field due to

an infinitely long straight charge with uniform charge density

an infinite plane sheet of charge of q.

17. What is a capacitor? Define its capacitance.

18. Explain the principle of capacitor. Deduce an expression for the capacitance of the parallel plate capacitor.

19. What is dielectric ? Explain the effect of introducing a dielectric slab between the plates of parallel plate capacitor.

20. A parallel plate capacitor is connected to a battery. If the dielectric slab of thickness equal to half the plate separation is inserted between the plates what happens to (i) capacitance of the capacitor (ii) electric field between the plates (iii) potential difference between the plates.

Deduce an expression for the equivalent capacitance of capacitors connected in series and parallel.

21. What is meant by dielectric polarisation?

22. State the principle and explain the construction and working of Van de Graaff generator.

23. Why is it safer to be inside a car than standing under a tree during lightning?

UNIT 2 Current Electricity

1. Why is copper wire not suitable for a potentiometer?

2. Explain the flow of charges in a metallic conductor.

3. Distinguish between drift velocity and mobility. Establish a relation between drift velocity and current.

4. State Ohm’s law.

5. Define resistivity of a material. How are materials classified based on resistivity?

6. Write a short note on superconductivity. List some applications of superconductors.

7. The colours of a carbon resistor is orange, orange, orange. What is the value of resistor?

8. Explain the effective resistance of a series network and parallel network.

9. Discuss the variation of resistance with temperature with an expression and a graph.

10. Explain the determination of the internal resistance of a cell using voltmeter.

11. State and explain Kirchoff’s laws for electrical networks.

12. Describe an experiment to find unknown resistance and temperature coefficient of resistance using metre bridge?

Define the term specific resistance. How will you find this using a metre bridge?

1. Explain the principle of a potentiometer. How can emf of two cells be compared using potentiometer?

2. Distinguish between electric power and electric energy

3. State and Explain Faraday’s laws of electrolysis. How are the laws verified experimentally?

4. Explain the reactions at the electrodes of (i) Daniel cell (ii) Leclanche cell

5. Explain the action of the following secondary cell.

6. lead acid accumulator

7. Why automobile batteries have low internal resistance?

UNIT 3 Effects of Electric Current

1. State Joule’s law

2. Explain Joule’s calorimeter experiment to verify Joule’s laws of heating.

3. Define Peltier coefficient

4. Define Thomson coefficient

5. State Biot – Savart law

6. Obtain an expression for the magnetic induction at a point due to an infinitely long straight conductor carrying current.

Deduce the relation for the magnetic induction at a point along the axis of a circular coil carrying current.

1. Explain in detail the principle, construction and theory of a tangent galvanometer.

2. What is Ampere’s circuital law?

3. Applying Amperes circuital law, find the magnetic induction due to a straight solenoid.

4. Define ampere

5. Deduce an expression for the force on a current carrying conductor placed in a magnetic field.

6. Explain in detail the principle, construction and the theory of moving coil galvanometer.

7. Explain how you will convert a galvanometer into (i) an ammeter and (ii) a voltmeter.

UNIT 4 Electromagnetic Induction and Alternating Current

1. What is electromagnetic induction?

2. State Faraday’s laws of electromagnetic induction.

3. Define self−inductance. Give its unit

4. Define the unit of self−inductance.

5. Define coefficient of mutual induction.

6. Give the practical application of self−induction.

7. State Fleming’s right hand rule.

8. Define rms value of a.c.

9. State the methods of producing induced emf.

10. What is a poly phase AC generator?

11. What is inductive reactance?

12. Define alternating current and give its expression.

13. What is capacitive reactance?

14. Mention the difference between a step up and step down transformer.

15. What is resonant frequency in LCR circuit?

16. Define power factor.

17. Why a d.c ammeter cannot read a.c?

18. Obtain an expression for the rms value of a.c.

19. Define quality factor.

20. A capacitor blocks d.c but allows a.c. Explain.

21. What happens to the value of current in RLC series circuit, if frequency of the source is increased?

22. State Lenz’s law and illustrate through an experiment. Explain how it is in accordance with the law of conservation of energy.

23. Differentiate between self−inductance and mutual inductance.

24. Obtain an expression for the self−inductance of a long solenoid.

25. Explain the mutual induction between two long solenoids. Obtain an expression for the mutual inductance.

26. Explain how an emf can be induced by changing the area enclosed by the coil.

27. Discuss with theory the method of inducing emf in a coil by changing its orientation with respect to the direction of the magnetic field.

28. What are eddy currents? Give their applications. How are they minimised?

29. Explain how power can be transmitted efficiently to long distance.

30. Obtain an expression for the current flowing in a circuit containing resistance only to which alternating emf is applied. Find the phase relationship between voltage and current.

31. Obtain an expression for the current in an ac circuit containing a pure inductance. Find the phase relationship between voltage and current.

32. Obtain an expression for the current flowing in the circuit containing capacitance only to which an alternating emf is applied. Find the phase relationship between the current and voltage.

33. Derive an expression for the average power in an ac circuit.

34. Describe the principle, construction and working of a choke coil.

35. Discuss the advantages and disadvantages of a.c. over dc.

36. Describe the principle, construction and working of a single – phase a.c generator.

37. Describe the principle, construction and working of three−phase a.c generator.

38. Explain the principle of transformer. Discuss its construction and working.

39. A source of altemating emf is connected to a series combination of a resistor R an inductor L and a capacitor C. Obtain with the help of a vector diagram and impedance diagram, an expression for

a. the effective voltage (ii) the impedance (iii) the phase relationship between the current and the voltage.

UNIT 5 Electromagnetic Waves and Wave Optics

1. What are electromagnetic waves?

2. Mention the characteristics of electromagnetic waves.

3. Give the source and uses of electromagnetic waves.

4. Explain emission and absorption spectra.

5. What is fluoresence and phosphorescence?

6. Distinguish the corpuscle and photon.

7. What is Tyndal Scattering?

8. How are Stoke’s and Anti-stoke’s line formed?

9. Why the sky appears blue in colour?

10. Explain the Raman scattering of light.

11. Explain Huygen’s principle.

12. On the basis of wave theory, explain total internal reflection.

13. What is principle of superposition of waves?

14. Give the conditions for sustained interference.

15. Derive an expression for bandwidth of interference fringes in Young’s double slit experiment.

16. Discuss the theory of interference in thin transparent film due to reflected light and obtain condition for the intensity to be maximum and minimum.

17. What are Newton’s rings? Why the centre of the Newton’s rings is dark?

18. Distinguish between Fresnel and Fraunhofer diffraction.

19. Discuss the theory of plane transmission grating.

20. Describe an experiment to demonstrate transverse nature of light.

21. Differentiate between polarised and unpolarised light.

22. State and explain Brewster’s law.

23. Bring out the difference’s between ordinary and extra ordinary light.

24. Write a note on : (a) Nicol prism (b) Polaroid

25. What is meant by optical rotation? On what factors does it depend?

UNIT 6 : Atomic Physics

1. What are cathode rays?

2. Write the properties of cathode rays.

3. Describe the J.J. Thomson method for determining the specific charge of electron.

4. Describe Millikan’s oil drop experiment to determine the charge of an electron.

5. Explain the results of Rutherford α−particle scattering experiment.

6. What are the drawbacks of Rutherford atom model?

7. State the postulates of Bohr atom model.

8. Obtain the expression for the radius of the n^th orbit of an electron based on Bohr’s theory.

9. Prove that the energy of an electron for hydrogen atom in n^th orbit is En=me⁴/8ε_o2_n 2_h

10. Explain the spectral series of hydrogen atom.

11. What is meant by energy level diagram?

12. What are the drawbacks of Sommerfeld atom model?

13. Define : excitation potential energy and ionization potential energy.

14. What are X−rays?

15. What are hard X-rays and soft x-rays?

16. Write the properties of X –rays?

17. Why ordinary plane transmission gratings cannot be used to produce diffraction effects in X−rays?

18. State and obtain Bragg’s law.

19. Explain how a Bragg’s spectrometer can be used to determine the wavelength of X−rays.

20. Explain the origin of characteristic x-rays.

21. State : Moseley’s law.

22. Write the differences between spontaneous emission and stimulated emission.

23. What is meant by normal population?

24. What are the important characteristics of laser?

25. How does the laser light differ from ordinary light?

26. Explain the working of Ruby laser with neat sketch.

27. With the help of energy level diagram, explain the working of He−Ne laser.

28. What are various applications of laser in medical field?

UNIT 7 : Dual Nature of Radiation and Matter and Relativity

1. What is photoelectric effect?

2. Define stopping potential.

3. Define threshold frequency.

4. Define work function.

5. Explain the variation of photoelectric current with applied voltage.

6. State the laws of photoelectric emission.

7. Explain Einstein’s theory of photoelectric effect

8. What are photo-cells?

9. What are the applications of photo-cells?

10. What are matter waves?

11. Derive an expression for de Broglie wavelength of matter waves.

12. Draw a neat sketch of an electron microscope. Explain its working.

13. Mention the applications of electron microscope.

14. Define frame of reference.

15. State the postulates of special theory of relativity.

16. Discuss the concept of space, time and mass.

17. Explain length contraction.

18. Explain time dilation.

19. If a body moves with the velocity of light, what will be its mass? Comment on your result.

20. Derive Einstein’s mass energy equivalence.

UNIT 8 : Nuclear Physics 83

1. With example explain the classification of the nuclei in terms of its proton number and neutron number.

2. Explain mass defect and binding energy.

3. Calculate the energy equivalence of 1 atomic mass unit.

4. Show that nuclear density is almost a constant for all the nuclei.

5. Explain the variation of binding energy with mass number by a graph and discuss its features.

6. Discuss the principle and action of a Bainbridge mass spectrometer to determine the isotopic masses.

7. Explain the different characteristics of nuclear forces.

8. Define radioactivity.

9. Explain the Soddy−Fajan’s radioactive displacement law.

10. Obtain an expression to deduce the amount of the radioactive substance present at any moment.

11. Obtain the relation between half−life period and decay constant.

12. Define curie.

13. What do you mean by artificial radioactivity?

14. What are the applications of radio-isotopes?

15. Explain the construction and working of a Geiger−Muller Counter.

16. How do you classify the neutrons in terms of its kinetic energy?

17. What is artificial transmutation?

18. Explain how liquid drop model of the nucleus can account for nuclear fission.

19. With a neat sketch, explain the working of a nuclear reactor.

20. What is meant by breeder reactor?

21. What are thermonuclear reactions?

22. Explain how carbon−nitrogen cycle can account for the production of stellar energy.

23. What are cosmic rays?

24. Explain the latitude effect of cosmic rays.

25. Explain how the intensity of the cosmic rays changes with altitude.

26. Explain how a cosmic ray shower is formed.

27. How do you classify the elementary particles into four groups?

28. Describe the valence band, conduction band and forbidden energy gap with the help of energy level diagram.

29. Describe the energy band structure of insulator, semiconductor and conductor.

30. What do you understand by intrinsic and extrinsic semiconductor?

31. What is rectification?

32. Explain the working of a half wave diode rectifier.

33. Explain the working of bridge rectifier.

34. What is zener breakdown?

35. Describe the construction of Zener diode.

36. Explain with necessary circuit how zener diode can be used as a voltage regulator.

37. Describe the working of PNP and NPN transistors.

38. Deduce the relation between α and β of a transistor.

39. Explain an experiment to determine the characteristics of a transistor in CE configuration. Explain how the transistor parameters can be evaluated.

40. Why is a transistor called as current amplification device?

41. Why CE configuration is preferred over CB configuration for operating transistor as an amplifier?

42. Describe the working of a transistor amplifier.

43. Define bandwidth of an amplifier.

44. What is meant by feedback? Name the two types of feedback.

45. Derive an expression for voltage gain of an amplifier with negative feedback.

46. What are the advantages of negative feedback?

47. Give the Barkhausen criteria for oscillations.

48. Sketch the circuit of Colpitt’s oscillator. Explain its working.

49. Give the function of ‘OR’ and ‘NAND’ gates.

50. What are universal gates? Why are they called so?

51. What is an EXOR gate? Give the Boolean expression for the EXOR operation.

UNIT 9 : Semiconductor Devices and their Applications

1. State and prove DeMorgan’s theorems.

2. What is an integrated circuit?

3. Identify the analog and digital signals from the following.

a. square wave, (ii) sine wave

4. Differentiate between linear ICs and digital ICs.

5. Describe an operational amplifier. Explain its action as (i) inverting amplifier and (ii) noninverting amplifier.

6. Explain the term virtual ground of an operational amplifier.

7. Give the important parameters of an operational amplifier.

8. Explain how operational amplifier is used as a summer.

9. Describe the action of an operational amplifier as difference amplifier.

10. Explain how multimeter is used as ohm meter.

UNIT 10 : Communication Systems

1. What are the different types of radio wave propagation?

2. Explain the ground wave propagation.

3. Explain the wave propagation in ionosphere.

4. What is meant by skip distance?

5. What is the necessity of modulation?

6. Explain amplitude modulation.

7. Define modulation factor.

8. Define bandwidth.

9. What are the limitations of amplitude modulation?

10. Explain frequency modulation.

11. What is phase modulation?

12. Define directivity.

13. Draw the block diagram of AM radio transmitter.

14. Explain the function of FM transmitter with neat block diagram.

15. What is meant by scanning?

16. What is interlaced scanning?

17. Explain the function of a vidicon camera tube.

18. Explain the functions of various units in the monochrome television transmission.

19. Explain the functional block diagram of a monochrome TV receiver.

20. Explain the principle of radar.

21. What are the applications of radar?

22. Explain the principle of modem.

23. What are the different types of wire and cable used for telecommunication system ?

24. What are the advantages of fiber optic communication system?

In a broadcasting studio, a 1000 kHz carrier is modulated by an audio signal of frequency range, 100−5000 Hz. Find (i) maximum and minimum frequencies of USB (ii) maximum and minimum frequencies of LSB and (iii) width of the channel.

SYLLABUS (180 periods)

UNIT – 1 ELECTROSTATICS (18 periods)

Frictional electricity, charges and their conservation; Coulomb’s law – forces between two point electric charges. Forces between multiple electric charges – superposition principle.

Electric field – Electric field due to a point charge, electric field lines; Electric dipole, electric field intensity due to a dipole –behavior of dipole in a uniform electric field – application of electric dipole in microwave oven.

Electric potential – potential difference – electric potential due to a point charge and due a dipole. Equipotential surfaces – Electrical potential energy of a system of two point charges.

Electric flux – Gauss’s theorem and its applications to find field due to (1) infinitely long straight wire (2) uniformly charged infinite plane sheet (3) two parallel sheets and (4) uniformly charged thin spherical shell (inside and outside)

Electrostatic induction – capacitor and capacitance – Dielectric and electric polarisation – parallel plate capacitor with and without dielectric medium – applications of capacitor – energy stored in a capacitor. Capacitors in series and in parallel – action of points – Lightning arrester – Van de Graaff generator.

UNIT - 2 CURRENT ELECTRICITY (11 periods)

Electric current – flow of charges in a metallic conductor – Drift velocity and mobility and their relation with electric current.

Ohm’s law, electrical resistance. V-I characteristics – Electrical resistivity and conductivity. Classification of materials in terms of conductivity – Superconductivity (elementary ideas) – Carbon resistors

– colour code for carbon resistors – Combination of resistors – series and parallel – Temperature dependence of resistance – Internal resistance of a cell – Potential difference and emf of a cell.

Kirchoff’s law – illustration by simple circuits – Wheatstone’s Bridge and its application for temperature coefficient of resistance measurement – Metrebridge – Special case of Wheatstone bridge – Potentiometer – principle – comparing the emf of two cells.

Electric power – Chemical effect of current – Electro chemical cells Primary (Voltaic, Lechlanche, Daniel) – Secondary – rechargeable cell – lead acid accumulator.

UNIT – 3 EFFECTS OF ELECTRIC CURRENT (15 periods)

Heating effect. Joule’s law – Experimental verification. Thermoelectric effects – Seebeck effect – Peltier effect – Thomson effect – Thermocouple, thermoemf, neutral and inversion temperature. Thermopile.

Magnetic effect of electric current – Concept of magnetic field, Oersted’s experiment – Biot-Savart law – Magnetic field due to an infinitely long current carrying straight wire and circular coil – Tangent galvanometer – Construction and working – Bar magnet as an equivalent solenoid – magnetic field lines.

Ampere’s circuital law and its application.

Force on a moving charge in uniform magnetic field and electric field – cyclotron – Force on current carrying conductor in a uniform magnetic field, forces between two parallel current carrying conductors

– definition of ampere.

Torque experienced by a current loop in a uniform magnetic field-moving coil galvanometer – Conversion to ammeter and voltmeter

– Current loop as a magnetic dipole and its magnetic dipole moment

– Magnetic dipole moment of a revolving electron.

UNIT – 4 ELECTROMAGNETIC INDUCTION AND ALTERNATING CURRENT (14 periods)

Electromagnetic induction – Faraday’s law – induced emf and current – Lenz’s law.

Self induction – Mutual induction – Self inductance of a long solenoid – mutual inductance of two long solenoids.

Methods of inducing emf – (1) by changing magnetic induction

(2) by changing area enclosed by the coil and (3) by changing the orientation of the coil (quantitative treatment) analytical treatment can also be included.

AC generator – commercial generator. (Single phase, three phase).

Eddy current – Applications – Transformer – Long distance transmission.

Alternating current – measurement of AC – AC circuit with resistance – AC circuit with inductor – AC circuit with capacitor - LCR series circuit – Resonance and Q – factor: power in AC circuits.

UNIT–5 ELECTROMAGNETIC WAVES AND WAVE OPTICS (17 periods)

Electromagnetic waves and their characteristics – Electromagnetic spectrum, Radio, microwaves, Infra red, visible, ultra violet – X rays, gamma rays.

Emission and Absorption spectrum – Line, Band and continuous spectra – Flourescence and phosphorescence.

Theories of light – Corpuscular – Wave – Electromagnetic and Quantum theories.

Scattering of light – Rayleigh’s scattering – Tyndal scattering – Raman effect – Raman spectrum – Blue colour of the sky and reddish appearance of the sun at sunrise and sunset.

Wavefront and Huygen’s principle – Reflection, Total internal reflection and refraction of plane wave at a plane surface using wavefronts.

Interference – Young’s double slit experiment and expression for fringe width – coherent source - interference of light. Formation of colours in thin films – analytical treatment – Newton’s rings.

Diffraction – differences between interference and diffraction of light – diffraction grating.

Polarisation of light waves – polarisation by reflection – Brewster’s law - double refraction - nicol prism – uses of plane polarised light and polaroids – rotatory polarisation – polarimeter

UNIT – 6 ATOMIC PHYSICS (16 periods)

Atomic structure – discovery of the electron – specific charge (Thomson’s method) and charge of the electron (Millikan’s oil drop method) – alpha scattering – Rutherford’s atom model.

Bohr’s model – energy quantisation – energy and wave number expression – Hydrogen spectrum – energy level diagrams – sodium and mercury spectra - excitation and ionization potentials. Sommerfeld’s atom model.

X-rays – production, properties, detection, absorption, diffraction of X-rays – Laue’s experiment – Bragg’s law, Bragg’s X-ray spectrometer – X-ray spectra – continuous and characteristic X–ray spectrum – Mosley’s law and atomic number.

Masers and Lasers – spontaneous and stimulated emission – normal population and population inversion – Ruby laser, He–Ne laser

– properties and applications of laser light – holography

UNIT – 7 DUAL NATURE OF RADIATION AND MATTER – RELATIVITY (10 periods)

Photoelectric effect – Light waves and photons – Einstein’s photo

– electric equation – laws of photo – electric emission – particle nature of energy – photoelectric equation – work function – photo cells and their application.

Matter waves – wave mechanical concept of the atom – wave nature of particles – De–Broglie relation – De–Broglie wave length of an electron – electron microscope.

Concept of space, mass, time – Frame of references. Special theory of relativity – Relativity of length, time and mass with velocity

– (E = mc²).

UNIT – 8 NUCLEAR PHYSICS (14 periods)

Nuclear properties – nuclear Radii, masses, binding energy, density, charge – isotopes, isobars and isotones – Nuclear mass defect

– binding energy. Stability of nuclei-Bain bridge mass spectrometer.

Nature of nuclear forces – Neutron – discovery – properties – artificial transmutation – particle accelerator

Radioactivity – alpha, beta and gamma radiations and their properties, α-decay, β-decay and γ-decay – Radioactive decay law – half life – mean life. Artificial radioactivity – radio isotopes – effects and uses Geiger – Muller counter.

Radio carbon dating – biological radiation hazards

Nuclear fission – chain reaction – atom bomb – nuclear reactor

– nuclear fusion – Hydrogen bomb – cosmic rays – elementary particles.

UNIT – 9 SEMICONDUCTOR DEVICES AND THEIR APPLICATIONS (26 periods)

Semiconductor theory – energy band in solids – difference between metals, insulators and semiconductors based on band theory

– semiconductor doping – Intrinsic and Extrinsic semi conductors.

Formation of P -N Junction – Barrier potential and depletion layer. – P-N Junction diode – Forward and reverse bias characteristics

– diode as a rectifier – zener diode. Zener diode as a voltage regulator

– LED.

EXPERIMENTS (12 × 2 = 24 periods)

To determine the refractive index of the material of the prism by finding angle of prism and angle of minimum deviation using a spectrometer.

To determine wavelengths of a composite light using a diffraction grating and a spectrometer by normal incidence method (By assuming N).

To determine the radius of curvature of the given convex lens using Newton’s rings experiment.

To find resistance of a given wire using a metre bridge and hence determine the specific resistance of the material.

To compare the emf’s of two primary cells using potentiometer.

To determine the value of the horizontal component of the magnetic induction of the earth’s magnetic field, using tangent galvanometer.

To determine the magnetic field at a point on the axis of a circular coil.

To find the frequency of the alternating current (a.c) mains using a sonometer wire.

(a) To draw the characteristic curve of a p-n junction diode in forward bias and to determine its forward resistance.

To draw the characteristic curve of a Zener diode and to determine its reverse breakdown voltage.

To study the characteristics of a common emitter NPN transistor and to find out its input, output impedances and current gain.

Construct a basic amplifier (OP amp) using IC 741 (inverting, non inverting, summing).

Study of basic logic gates using integrated circuits NOT, AND, OR, NAND, NOR and EX-OR gates.