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#### Important 5 Mark Creative Questions (New Syllabus 2020)

12th Standard EM

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Physics

Time : 01:00:00 Hrs
Total Marks : 160

Part A

32 x 5 = 160
1.  It requires 50 μJ of work to carry a 2C charge from point R to S. What is the potential difference between these points?

2. What charge would be required to electrify a sphere of radius 25cm. So as to get a surface charge density of $\frac{3}{\pi}$ cm-1?

3. A parallel plate capacitor has plate area, 25 cm+2 and a separation of 2 mm between the plates. The capacitor is connected to a battery of 12V. Find the charge on the capacitor.

4. Two insulated charged copper sphere A and B have their centres separated by a distance of 50cm.
(i) What is the force of electrostatic repulsion, if the charge on each is 6.5 X 10-7C and the radii of A and B are negligible compared to the distance of separation?
(ii) What is the force of repulsion, if each sphere is charged double the above amount and the distance between them is halved?

5. Write mathematical relation between mobility & drift velocity of charge carriers in a conductor (ii) mobility & relaxation time (or) mean free time.

6. The lengths &radii of three wires of same metal in the radio 2: 3 :4 & 3 :4 : 5 respectively. They are joined in parallel & included in a circuit having 5 A current. Find current in each wire.

7. A potential difference of 3V is applied across a conductor through which SA of current is flowing. Determine the resistane of the conductor.

8. 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.

9. What difference between soft ferromagnetic materials and hard ferromagnetic materials.

10. A magnetised needle of magnetic moment 3.6 x 10-2T-1 is placed at 30° with the direction of uniform magnetic field of magnitude 2 x 10-2T. Calculate the torque acting on the needle.

11. A galvanometer of resistance 15Ω gives full scale deflection for a current of 2mA. Calculate the shunt resistance needed to convert it into an ammeter of range 0 to 5A.

12. Derive an expression for the RMS value of AC.

13. What is alternating current? Write an expression for its instantaneous value and write the frequency of DC.

14. A rectangular loop of area 20cm x 30cm is placed in a magnetic field of 0.3T with its plane
(i) normal to the field
(ii) inclined 30° to the field and
(iii) parallel to the field. Find the flux linked with the coil in each case.

15. Show how to generalize Ampere's circuital law to include the term due to displacement current?

16. About 5 % of the power of a 100 W light bulb is connected to visible radiation. What is the average intensity of visible radiation at the distance of 1m from the bulb?

17. (I) For a glass ( $\mu =\sqrt { 5 }$) the angle of minimum deviation is equal to the angle of the prism. Find the angle ofthe prism.
(ii) Draw ray diagram when incident ray falls normally on one of the two equal sides of a right angled isosceles prism having refractive inded $\mu =\sqrt { 3 }$.

18. A concave lens is kept in contact with a convex lens of focal length 20 cm. The combination behaves as a convex lens of focal length 50 cm. Find the power of concave lens.

19. Light falls from glass (μ = 1.5) to air. Find the angle of incidence for which the angle of deviation is 900

20. Explain the production of x-rays.

21. Write the expression for the de Broglie wavelength associated with a charged particle having charge 'q' and mass 'm', when it is accelerated by a potential V.

22. Plot a graph showing the variation of photoelectric current with intensity of light. The work function for the following metals is given. Na: 2.75 eV and Mo: 4.175 eV.  Which of these will not give photoelectron emission from a radiation of wavelength 3300 Å from a laser bean?

23. Monochromatic light of frequency 6 x 1014 Hz is produced by a laser. The power emitted is 2.0 x 10-3 W. How many photons per second on an average are emitted by the source?

24. (i) Define the term 'intensity of radiation' in photon picture.
(ii) Plotagraph showing the variation of photo current vs collector potential for three
different intensities I1 > I2> I3 two of which (I1 and I2) have the same frequency v and the third has frequency v1 > v.
(iii) Explain the nature of the curves on the basis of Einstein's equation.

25. 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.

26. Write briefly the underlying principle used in Davision - Germer experiment to verify wave nature of electrons experimentally. What is the de-Broglie wavelength of an electron with kinetic energy (KE) 120 eV?

27. What are the drawbacks of Rutherford atom model?

28. The binding energies per nucleon for deuteron $(_{ 1 }^{ 2 }{ H })$ and helium $(_{ 2 }^{ 4 }{ He) }$ are 1.1 MeV and 7 MeV respectively. Determine the energy released when two deuterons fuse to form a helium nucleus $(_{ 2 }^{ 4 }{ He) }$

29. The half-life of radium is 1600 years. After how many years 25% of radium block remains undecayed?

30. A power reactor develops energy at the rate of 30,000 kW. How many gram of 235U would be consumed daily? Assuming that on an average 200 MeV energy is released per fission.

31. Explain current transfer characteristics.

32. Write the applications of mobile communication.