#### 12th Standard Physics English Medium Reduced Syllabus Important Questions with Answer key - 2021 Part - 1

12th Standard

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Physics

Time : 01:00:00 Hrs
Total Marks : 100

Multiple Choice Questions

10 x 1 = 10
1. By using law of conservation of electric charge balance the following equations:
92U238 90Th234 ________.

(a)

2He4

(b)

1H3

(c)

1H2

(d)

1H1

2. There is a current of 1.0 A in the circuit shown below. What is the resistance of P ?

(a)

1.5 Ω

(b)

2.5 Ω

(c)

3.5 Ω

(d)

4.5 Ω

3. An unknown resistance is connected in parallel with a 15$\Omega$ resistance and a 12V battery. What is the value of the unknown resistance if the current in the circuit is 2A?

(a)

$10\Omega$

(b)

$20\Omega$

(c)

$30\Omega$

(d)

$40\Omega$

4. The instantaneous values of alternating current and voltage in a circuit are $i=\frac { 1 }{ \sqrt { 2 } } sin\left( 100\pi t \right)$ A and v=$=\frac { 1 }{ \sqrt { 2 } } sin\left( 100\pi t+\frac { \pi }{ 3 } \right) V.$The average power in watts consumed in the circuit is

(a)

$\frac{1}{4}$

(b)

$\frac{\sqrt3}{4}$

(c)

$\frac{1}{2}$

(d)

$\frac{1}{8}$

5. Lenz's law is in accordance with the law of

(a)

conservation of charges

(b)

conservation of flux

(c)

conservation of momentum

(d)

conservation of energy

6. In LCR circuit when KL = Xc (at resonance) the current _________________

(a)

is zero

(b)

is in phase with the voltage

(c)

(d)

lags behind the voltage

7. Quality factor = ?

(a)

$\frac{output \ power}{input \ power}$

(b)

$\frac{output \ current}{input \ current}$

(c)

$\frac{voltage \ across \ L (or) \ C}{applied \ voltage}$

(d)

$\frac{random \ frequency}{resonant \ frequency}$

8. The fig. represents the observed intensity of X-rays emitted by an X-ray tube as a function of wavelength. The sharp peaks A and B denote

(a)

continuous spectrum

(b)

band spectrum

(c)

characteristic spectrum

(d)

9. A Coolidge tube operates at 18600 V. The maximum frequency of X-radiation emitted from it is _________

(a)

4.5 x1018 Hz

(b)

45 x 1018 Hz

(c)

4.05 x 1018 Hz

(d)

45.5 x 1018 Hz

10. In a N-P-N transistor circuit, the emitter, collector and base current are respectively IE, IC and lB. The relation between them is

(a)

ICEB

(b)

IBCE

(c)

IB>IC>IE

(d)

IB>IC>IE

11. 2 Marks

15 x 2 = 30
12. Two charge d spherical conditioners of radii R1 & R2 when connected by a conducting wire acquire charges q1 & q2 respectively. Find the ratio of surface charge densities in terms of their radii.

13. Derive the expression for power P=VI in electrical circuit.

14. Write down the various forms of expression for power in electrical circuit.

15. Why are resistor connected in series and in parallel (i) To increase the resistor of the circuit. the resistor are connected in series.

16. Why are connecting resistors in a metrebridge made of thick copper strips?

17. State Maxwell's right hand cork screw rule?

18. Where on the earth's surface is the value of
(i) angle of dip maximum
(ii) vertical component of earth's magnetic field zero

19. What for an inductor is used? Give some examples.

20. How will you define RMS value of an alternating current?

21. Explain the use of transformers in long distance transmission of electric power

22. When does the phenomenon of resonance is possibble in the circuit?

23. Draw a graph showing the variation of reactance of
(i) a capacitor and
(ii) an inductor with the frequency of an a.c circuit.

24. What is spectrum?

25. A deuteron and an alpha particle are accelerated with the same potential. Which I one of the two has i) greater value of de Broglie wavelength associated with it and
ii) less kinetic energy? Explain.

26. Give the factors that are responsible for transmission impairments.

27. 3 Marks

15 x 3 = 45
28. The magnetic field shown in the figure is due to the current carrying wire. In which
direction does the current flow in the wire?.

29. Deduce the relation for the magnetic induction at a point due to an infinitely long straight conductor carrying current.

30. A circular loop carrying current I show the direction of the magnetic field with the help of lines of force.

31. A rectangular current carrying loop placed 2cm away from a long, street, current - carrying conductors. What is the direction and magnitude of the net force acting on the loop.

32. Establish the fact that the relative motion between the coil and the magnet induces an emf in the coil of a closed circuit.

33. Show that Lenz’s law is in accordance with the law of conservation of energy.

34. Derive an expression for phase angle between the applied voltage and current in a series RLC circuit.

35. What is impedance? When does LCR circuit have minimum impedance?

36. Write down Maxwell equations in integral form.

37. Discuss briefly the experiment conducted by Hertz to produce and detect electromagnetic spectrum.

38. Name the parts of Electromagnetic spectrum which is
(i) used to destroy becteria.
(ii) produced by where is a sudden deceleration of high speed electrons.
(iii) used in food industry.

39. (i) Draw a graph showing variation of photoelectric current (I) with anode potential (V) for different intensities of incident radiation. Name the characteristic of the incident radiation that is kept constant in this experiment.
(ii) If the potential difference used to accelerate electrons is doubled, by what factor does the de-Broglie wavelength associated with the electrons change?

40. What are radioactive elements? What are the factors that affect radio activity?

41. Draw the circuit diagram' of a half wave rectifier and explain its working

42. Consider an ideal junction diode. Find the value of current flowing through AB is

43. 5 Marks

15 x 5 = 75
44. In the circuit shown in figure. Find
(i) The equivalent capacitance and
(ii) The charge stored in each capcicitor

45. Calculate the current that flows in the 1 Ω resistor in the following circuit.

46. A conductor of length I is connected to d.c. source of potential V. If the length of the conductor is doubled by streating it, keeping V constant, explain how do the following factors vary in the condcutor (I) Drift velocity. (ii) Resistor (ill) Resistivity.

47. Using the concept of drift velocity of charge carries in a conductor, deduce the relationship between circuit density and resistivity of the conductor?

48. In a wheat stone bridge circuit P = 7, Q = 8 , R = 12 & s = 7. Find the additional resistance to be used in series with S, so that the bridge is balanced.

49. A cyclotron's frequency is 8μHz. What should be the operating magnetic field for accelerating protons? If the radius of its dees is 50cm. calculate the k.E (is μeV) of the proton beam produced by the accelerator.

50. An inverter is common electrical device which we use in our homes. When there is no power in our house, inverter gives AC power to run a few electronic appliances like fan or light. An inverter has inbuilt step-up transformer which converts 12 V AC to 240 V AC. The primary coil has 100 turns and the inverter delivers 50 mA to the external circuit. Find the number of turns in the secondary and the primary current.

51. The current in an inductive circuit is given by 0.3 sin (200t – 40°) A. Write the equation for the voltage across it if the inductance is 40 mH.

52. Define Power in AC circuits? Derive an relation between true power & virtual power?

53. The instantaneous current and voltage of an a.c circuit are given by i = 10 sin 314t A and V = 50 sin (314t + π/2)V. What is the power dissipation in the circuit?

54. An AC generator consists of a coil of 1000 turns and cross. sectional area of 100 cm2, rotating at an angular speed of 100 rpm in a uniform magnetic field of 1.6 x 10-2 T calculate the maximum emf produced in the coil

55. In an electric circuit, there is a capacitor of reactance 100 Ω connected across the source of 220 V, find the displacement current.

56. An electron microscope uses electrons accelerated by a voltage of 50 kV. Determine the de Broglie wavelength associated with the electrons. If other factors (such as numerical aperture etc.) are taken to be roughly the same, how does the resolving power of an electron, microscope compare with that of an optical microscope which uses yellow light? Given : wavelength of yellow light = 5990 Á.

57. (a) A hydrogen atom is excited by radiation of wavelength 97.5 nm. Find the principal quantum number of the excited state.
(b) Show tliat the total number of lines in emission spectrum is $\frac { n(n-1) }{ 2 }$ and compute the total number of possible lines in emission spectrum

58. Assuming that energy released by the fission of a single $_{ 92 }^{ 235 }{ U }$ nucleus is 200MeV, calculate the number of fissions per second required to produce 1 watt power.