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#### Sample 3 Mark Book Back Questions (New Syllabus) 2020

12th Standard EM

Reg.No. :
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Physics

Time : 01:00:00 Hrs
Total Marks : 53

Part A

31 x 3 = 93
1. Calculate the number of electrons in one coulomb of negative charge.

2. Calculate the electric field at points P, Q for the following two cases, as shown in the figure.
(a) A positive point charge +1 μC is placed at the origin.
(b) A negative point charge -2 μC is placed at the origin.

3. Explain in detail Coulomb’s law and its various aspects.

4. Discuss the various properties of conductors in electrostatic equilibrium.

5. A potential difference across 24 Ω resistor is 12 V. What is the current through the resistor?

6. Resistance of a material at 100C and 400C are 45 Ω and 85 Ω respectively. Find its temperature co-efficient of resistance.

7. How the emf of two cells are compared using potentiometer?

8. Let the magnetic moment of a bar magnet be $\overset { \rightarrow }{ { p }_{ m } }$ whose magnetic length is d = 2l and pole strength is qm. Compute the magnetic moment of the bar magnet when it is cut into two pieces
(a) along its length
(b) perpendicular to its length.

9. Show the time period of oscillation when a bar magnet is kept in a uniform magnetic field is
$T=2\pi \sqrt { \frac { 1 }{ { p }_{ m }B } }$ in second, where I represents moment of inertia of the bar magnet, pm is the magnetic moment and is the magnetic field

10. Two materials X and Y are magnetised, whose intensity of magnetisation are 500
A m-1 and 2000 A m-1, respectively. If the magnetising field is 1000 A m-1, then which
one among these materials can be easily magnetized?.

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

12. Explain the principle and working of a moving coil galvanometer.

13. A circular antenna of area 3 m2 is installed at a place in Madurai. The plane of the area of antenna is inclined at 47o with the direction of Earth’s magnetic field. If the magnitude of Earth’s field at that place is 40773.9 nT find the magnetic flux linked with the antenna.

14. The self-inductance of an air-core solenoid is 4.8 mH. If its core is replaced by iron core, then its self-inductance becomes 1.8 H. Find out the relative permeability of iron.

15. Obtain an expression for motional emf from Lorentz force.

16. How are the three different emfs generated in a three-phase AC generator? Show the graphical representation of these three emfs.

17. Compare the electromagnetic oscillations of LC circuit with the mechanical oscillations of block-spring system to find the expression for angular frequency of LC oscillators mathematically.

18. Explain the Maxwell’s modification of Ampere’s circuital law.

19. Derive the equation for effective focal length for lenses in out of contact

20. Discuss about simple microscope and obtain the equations for magnification for near point focusing and normal focusing.

21. Light travelling through transparent oil enters in to glass of refractive index 1.5. If the refractive index of glass with respect to the oil is 1.25, what is the refractive index of the oil?

22. A monochromatic light is incident on an equilateral prism at an angle 30o and emerges at an angle of 75o. What is the angle of deviation produced by the prism?

23. Explain how frequency of incident light varies with stopping potential.

24. Briefly explain the principle and working of electron microscope.

25. Derive the energy expression for hydrogen atom using Bohr atom model.

26. Describe the working of nuclear reactor with a block diagram.

27. Calculate the radius of $_{ 79 }^{ 197 }{ Au }$ nucleus.

28. Explain the construction and working of a full wave rectifier.

29. State Boolean laws. Elucidate how they are used to simplify Boolean expressions with suitable example.

30. Elaborate on the basic elements of communication system with the necessary block diagram.

31. Elaborate any two types of Robots with relevant examples