# Important Questions for PHYSICS-XII

#### Important Questions for PHYSICS-XII

1. Resistors R1 and R2 are connected in series to an emf source that has negligible internal resistance. What happens to the current through Rwhen a third resistor R3 is connected in parallel with R2?
2. What is the difference between an emf and a potential difference? Under what circumstances are the potential difference between the terminals of a batter and the battery equal to each other?
3. A voltmeter has high resistance. Explain why?
4. A cylindrical rod has resistance R. If we double its length and diameter, what is its resistance in terms of ‘R’?
5. Why does an electric bulb nearly always burn out just as you turn on the light, almost never while the light is shining?
6. Can the potential difference between the terminals of a battery ever be opposite in direction to the emf?
7. “Good thermal conductors are also good electrical conductor” If so, why don’t the connecting wires that are used to connect heater get hot by conduction of heat from the heating element?
8. Two copper wires of different diameters are joined end – to – end. If a current flows in the wire combination, what happens to the drift velocity of the electrons when they move from the larger – diameter wire to the smaller – diameter wire?
9. When the ends of a wire are connected to a battery, initially the current is slightly larger, but soon it decreases slowly and becomes steady at a lower value although the emf of the battery remains unchanged. Explain.
10. Is there any difference between “resistance of a wire” and “resistivity of wire”? Explain
11. Two bulbs of different wattage are connected in series. Which buib will glow brighter? Why?
12. Batteries are always  labeled with their emf. Would it also be appropriate to put a label on batteries stating how much current they provide? Why or why not?
13. Sketch the symbols of “a capacitor”, “an inductor”, “emf of a cell” and “a resistor”
14. Give an example of non ohmic conductor and present its current voltage characteristic graph.
15. What is the ratio of maximum to minimum resistance obtainable from n wires of resistance R each?
16. Why is it essential that the resistance of a voltmeter by very high?
17. An ammeter is always connected in series. Why?
18. Distinguish between resistance and resistivity of material.
19. Long distance electric power, transmission lines always operate at very high voltage, sometime as much as 750 KV. What are the advantages of such high voltages?
20. The energy that can be extracted from a storage battery is always less that the energy that goes into it while charging. Why?
21. The resistance of an ammeter mush essentially be very small. Why?
22. A wire is stretched to double its length. What happens to its resistance?
23. Why do electrons acquire a steady drift velocity?
24. You are given 2 wires each of resistance R. what is the ration of maximum to minimum resistance that can be obtained from these wires?
25. Is terminal p.d. always greater than its emf?
26. Can the potential difference across a battery be greater than its emf?
27. Define drift velocity of electrons. Establish a relation between drift velocity of electrons and current density in the conductor.
28. Explain the theory of a) series and b) parallel combinations of resistances in an electric circuit
29. What is meant by a shunt? How will you convert a galvanometer into an ammeter?
30. State and explain Ohm’s law. Two resistors are connected in parallel and third be connected in series with the combination of parallel resistors. If this combination be connected with a battery of the negligible internal resistance find the potential difference across each resistor.
31. In the given figure, the current through the 3Ω resister is 0.8 A. Find the potential drop across 4Ω resister. 1. A cell of emf  18 V has an internal resistance of 3Ω. The terminal p. d. of the battery becomes 15 V when connected by a wire. Find the resistance of the wire.
2. A potential difference of 4.5 V is applied between the ends of wire that is 2.5 m long and has radius of 0.654 mm. The resulting current through the wire is 17.6 A. What is the resistivity of the wire?
3. A tightly coiled having 75 coils, each 3.50 cm in diameter, is made of insulated metal wire 3.25 mm in diameter. An ohm meter connected across its opposite end reads 1.7Ω. What is the receptivity of the metal?
4. A voltmeter coil has resistance 50Ω and a resister of 1.15K Ω is connected in series. It can read potential differences up to 12 volts. If the same coil is used to 1. Construct an ammeter which can measure currents up to 2A,what should be the resistance of the shunt used?
2. In the given figure, when switch  s is open, the voltmeter v reads 3.08v . when the switch is closed, the voltmeter reading drops to 2.97v, and the ammeter A reads 1.65A Find the emf, the internal resistance of the battery and the resister R. Assume that the two meters are ideal.
3. A resister of 500 Ohms and one of 2000 Ohms are placed in series with a 60 volt supply. What will be the reading on a voltmeter of internal resistance 2000 Ohmns when placed across (i) The 500Ω resistor and (ii) The 2000Ωresister? 1. What is the potential difference across 100Q resistor in the circuit given below
1. 1. Twelve cells each of emf 2 V and of internal resistance 0.5 ohm are arranged in a battery of n rows and an external resistance 0.4 ohm is connected to the poles of the battery. Estimate the current flowing through the resistance in terms of n.
2. As shown in the figure, a battery of emf24V and internal resistance r is connected to a circuit containing two parallel resistors of 3Ωand 6Ω in series with an 8Ω resistor. The current flowing in the 3Ω is 0.8A. calculate the current in the 6Ω resistor and the internal resistance of the cell
1. 1. A  battery of emf1.5V has a terminal p. d of 1.25V when a resistor of 25Ω is joined to it. Calculate the current flowing, the internal resistance and terminal p. d. when a resistance of 10Ω replaces 25Ω resistor.
2. In the given circuit, calculate the potential difference between the point B and D.
1. Why do we prefer a potential meter to measure emf of a cell rather than a voltmeter?
2.  Distinguish between wave fronts and wavelets.
3. A normally incident wave front does not deviate, when it travels from one medium to another. Explain
4. Can Snell's law be verified from wave theory? Explain with figure only.
5. What is wave front?
6. What is Huygen's principle?
7. When monochromatic light incidents on a surface, the reflected and refracted wave will have same frequency. Why?
8. State Huygen's principle/ does it apply to sound waves in air?
9.  Which parameters of light does not change on refraction?
10. Differentiate between a plane wave front and a spherical wave front.
11. State and explain Huygen's principle. Derive the law of reflection on the basis of this principle.
12. Describe Michelson's methods for the determination of speed of light.
13. State and explain Huygen's principle and use it to verify Snell's law.
14. Describe Foucault's Method to determine the velocity of light.
15. State Huygen's principle of wave theory of light and also use this principle to verify the laws of reflection of light.
16. State and use Huygen's principle of wave theory of light to verify the laws of refraction of light.
17. State and use Huygen's principle. Use it to prove Snell's law.
18. Describe Michelson's methods for the determine the velocity of light
19. Describe Foucault's Method to determination of speed of light.
20. 74.   Describe faccault's experimental method for the measurement of the velocity of light with necessary theory.
21. State and explain Huygen's principle. Use the principle to show that a plane wave incident obliquery  on a plane mirror is reflected as a plane wave so that the angle of incidence is equal to the angle of reflection.
22. Describe Michelson's Method to determination of speed of light. Write advantages of the method over foucault's method.
23. State and explain  Huygen's principle. Use the principle to show that a plane wave front incident obliquely on a plane reflecting surface is reflected as a plane wave front so that the angle of incidence is equal to the angle of reflection.
24. State and explain Huygen's principle. Use the principle to verify the laws of reflection of light on the basis of wave theory.
25. Define Huygen's principle and prove Snell's law by the help of wave theory of light.
26. Prove the laws of reflection of light using the wave theory.
27. State and explain  Huygen's principle. Use the principle to show that a plane wave front incident obliquely on a plane mirror  is reflected as a plane wave front so that the angle of incidence is equal to the angle of reflection.
28. A beam of light after reflection at a plane mirror, rotating 2000 times per minute, passes to a distant reflector. It returns to the rotating mirror from which it is reflected to make an angle of 1° with its original direction. If the distance between the mirrors is 6250m,calculate the velocity of light.
29. A  beam of light is  reflected by a rotating mirror on to a fixed mirror, which sends it back to the rotating mirror which it is again reflected making an angle of 18° with its original direction. The distance between the two mirrors is 10 km and the rotating mirror is making 375 revolutions per second. Calculate the velocity of light.
30. A  beam of light is  reflected by a rotating mirror on to a fixed mirror, which sends it back to the rotating mirror which it is again reflected, and then makes an angle of 18° with its original direction. The distance between  the two mirror is 104m and the rotating mirror is making 375 revolutions per second. Calculate the velocity of light.
31. A  beam of light is  reflected by a rotating mirror on to a fixed mirror, which sends it back to the rotating mirror from which it is again reflected and then makes an angle of 3.6° with the original direction. The distance between the two mirror is 1km and the rotating mirror is making 750 revs-1. Calculate the velocity of light.
32. The radius of curvature of the curved mirror is 200m and the plane mirror is rotated at 20 revs-1, calculate angle in degree between a ray incident on the plane mirror and then reflected from it after the light has travelled to the curved mirror and back to the plane mirror [C=3×108ms-1].
33. Can a charger particle move through a magnetic field with out experiencing my force? Explain
34. Does a chargerd particle moving through a magnetic field always experience a force? Explain
35. A current was sent through a helical coil spring \ the spring contracted, as if it had been compressed. Why?
36. If a magnetic force foes no work charged particles, how can it have any effect on the articles motion?
37. Can a charged particle move through a magnetic field with out experiencing any force? Explain the reason.
38. Two straight current carrying rods are replaced parallel to each other, how can 1(one ) ampere of current be defined from this arrangement?
39. An electron beam and a proton bream are moving parallel to each other is the beginning. Do they always maintain this status? Justify answer
40. State Ampere's circuital theorem.
41. A current carrying solenoid tends to contract. Why?
42. A horizontal wire, of length 5cm and carrying a current of 2A is placed in the middle of a long solenoid at right angles to its axis. The solenoid has 100 turns per meter and carries a steady current . calculate I if the force on the wire is equal to 10-4N(µ0=4π×10-7Hm-1)
43. A battery of 6V and internal reistance 0.5Ω is joimned in parallel with another of 10V and internal resistance 1Ω. The combination sends a current through an external resistance of 12Ω. Find the current through each battery.
44. The coil of a moving coil galvanometer has 50 turns and its resistance is 10Ω. It is replaced by a coil having 100 turns and resistance 50Ω. Find the factor by which the current and voltage sensitivities changes.
45. A horizontal straight wire, of mass 0.12gm and length 10cm cm is placed perpendicular to uniform horizontal magnetic field of flux density 0.6T. If the resistance per unit length of the wire is 3.8Ωm-1,calculate the potential difference that has to be applied between the end of the wire to make it just self supporting.
46. A copper wire has 1029 free electrons per cubic meter, a cross sectional area of 2mm2 and carries a current of 5 A. Calculate the force acting on each electron if the wore is now placed in a magnetic field of flux density 0.15 T which is perpendicular to the wire.
47. Two long parallel conductor carry respectively current of 12A and 8A in the same direction. If the wires are 10 cm apart, find where a third parallel wire also carrying a current must be placed so that the force experienced it will be zero.
48. An electron of K.E 10 eV is moving in a circular orbit of radius 11cm in a plane at right angles to a uniform magnetic field. Determine the value of the flux density. Mass of electron = 9.1×10-31kg, e=1.6×10-19C
49. A copper wire has 11029free electrons per cubic meter and crossectional area 2mm2 carries a current of 6A. calculate the force acting on each electron if the wire is now placed in uniform magnetic field of flux density 0.1T perpendicularly.
50. A  slice of indium antimonide is 2.5mm thick and carries a current of 150mA. A magnetic field of flux density 0.5T, correctly applied, produces a maximum Hall voltage of 8.75mV between the edges of the slice. Calculate the density of free charge carries, assuming they each have a charge of -1.6×10-19C.
51. A copper wire 28m long is wound into a flat circular coil 8.0 cm in diameter. If the current of 4.50 A flows through the coil, what is the magnetic induction at the center?
52. An alpha particle makes a full rotation in a circle of radius 1.0 meter in 2.0 sec. calculate the value of magnetic field induction at the center of the circle.(µ0=4π×10-7Hm-1)
53. A long wire carrying a current of 10A is placed perpendicular to magnetic field of flux density 5 Tesla. Calculate the force acting on 2m of the wire.
54. A stone is dropped from the top of the tower 300m high splashes into the water of a pond near the base, of the tower. When is the splash heard at the top? Given that the speed of sound in air is 340 m/s, g= 9.8 m/s [ ans= 8.70 s]
55.  A stone is dropped into a well and a splash is heard after 2.6 secs. Calculate the depth of the well. (Velocity of sound = 334m/s)
56. When a detonator is exploded on a railway line, an observer standing on the rail 2km away hears two sounds. What is the time interval between them? ( Y for steel= 2×1011N/m2, density of steel= 8000kg/m3, density of air= 1.4 kg/m3 and atmospheric  pressure = 105 N/m2 )   (Ans:- 5.9s)
57. The interval between the flash of lightning and the sound of thunder is 2 sec. When the temperature is 10 oC. How far the stormed if  the velocity at 0 oC is 330m/s.  (Ans:- 672m)
58. A plane progressive wave is represented by the equation
59. y= 0.1sin(200πt-20πx/17) where y and x are in mm and t is in sec, then find i) frequency ii)  wavelength iii) speed iv) phase difference between  two point 0.25m to 1.10 meter from O. v) equation of wave travelling in opposite direction with double amplitude.
60.  A plane progressive wave is y = 10–2 Sin (1024t – 25/8 x), where y is in centimeter, x meter and t in second. Find a) speed of wave, b) phase difference in radians between the points x = 1.5m and x = 1.66m.
61. A source of sound of frequency 550Hz emits waves of wavelength 600mm in air at 20oC. What will be the wavelength of sound at 0 oC.     (Ans:- 579mm)
62.  A man stationed between two parallel cliff fires a gun. He hears the first echo after 3sec and next after 5 sec. What is the distance between two cliffs?  Vair= 350m/s) (Ans:- 1400m)
63. A man standing at one end of closed corridor 57m long blow a blast of whistle. He found that the time from the blast to the sixth echo was 2 sec. if the temperature was 17 oC, what will be the velocity of sound at 0 oC?  (Ans;- 331.8m/s)
64. At what temperature velocity of sound in air is increased by 50% to that at 27 oC?
65. Two plane metal plates 4 cm long are held horizontally 3cm part in a vacuum, one being vertically above the other. The upper plate is at a potential of 300 V and the lower is earthed. Electrons having a velocity of 1.0x107 ms–1 are injected horizontally midway between the plates and in a direction parallel to the plates. Calculate the vertical deflection of the electron beam as it emerges form the plates. (e/m for electron = 1.8x1011Ckg–1)  ( Ans:- 1.44×10-2m)
66. An oil drop of man 3.25x10–15 kg falls vertically with uniform velocity, through the air between vertical parallel plates which are 2cm apart. When a p. d. of 1000V is applied to the plates the drop moves towards the negatively charge plate, it path being inclined at 450 to the vertical. Calculate the charge of oil drop. )  ( Ans:- 6.37×10-19C)
67.   Electron has velocity 3.52x10m/s and moves in a circular orbit in magnetic field 0.2T what will be the radius of the orbit? (Ans:-9.9×10-5m)
68.   An electron beam passes through a parallel plate capacitor with a velocity of       107m–1. The length of each plate is 10cm while the distance between the plates is 5cm. If the electric intensity between the plates is 20Vcm–1, find the acceleration and the angle of deflection of the beam. (Given e = 1.6 x 10–19 C and mass of electron 9.1 x 10–31 kg)
69. A beam of protons is accelerated from rest through a potential difference of 2000V and then enters a uniform magnetic field which is perpendicular to the direction of the proton beam. If the flux density is 0.2T, calculate the radius of the path which the beam describes. (proton mass: = 1.7x10–27, electronic charge = 1.6x10–19C)
70.   In a Miliken-type apparatus the horizontal plate are 1.5 cm apart. With the electric field switched off an oil drop is observed to fall with the steady velocity 2.5*10-2 cms-1. When the field is switched on the upper plate being positive, the drop just remains stationary when the potential different between the plates is 1500V. Calculate the radius of the drop and the number of electronic charges. (Given- density of oil=900kgm-3 and viscosity of air=1.8*10-5 NSm2, Neglect air density)