Tuesday, 16 September 2014

Class 12 important questions of EMI


                                                               "OM Sai Ram"
                                                             

Q.1. The magnitude of electric current is increasing from A towards B. If there is any induced current in the loop as shown in the fig what will be its direction?
Q.2 Which physical quantity is called the INERTIA OF ELECTRICITY? Why is its called so?
Q.3 Define 1 Henry.
Q.4 Two bar magnets are quickly moved towards a metallic loop connected across a
capacitor 'C' as shown in the figure. Predict the polarity of the capacitor.
 

Q.5 Name and state the law, which gives the direction of induced e.m.f. in
electromagnetic induction.
Q.6 What are eddy currents ? Write any two applications of eddy currents.
Q.7 What is the basic requirement to induce the electric current in a coil ?
Q.8 A current is induced in coil C1 due to the motion of current carrying coil C2.
(a) Write any two ways by which a large deflection can be obtained in the
galvanometer G. (b) Suggest an alternative device to demonstrate the induced current
in place of a galvanometer.


Q.9. In the figure given below, a bar magnet moving towards the right or left induces an e.m.f. in the coils (1) and (2). Find giving reason, the directions of the direction of the induced currents through the resistors AB and CD when the magnet is moving (a) towards the right, and (b) towards the left.
                                       
Q.10 The magnetic flux linked with a coil varies with time as Ф = 3t2 + 4t + 9 weber. What is the induced emf at t = 2 ?
 Q.11 A circular coil of radius 8 cm and 20 turns rotates about its vertical diameter with an
angular speed of 50 s-1 in a uniform horizontal magnetic field of magnitude 3 x 10-2 T. Find the
maximum and average value of the emf induced in the coil.
Q.12  Define self-inductance and give its S. I . unit. Derive an expression for self- inductance of
a long, air-cored solenoid of length l, radius r, and having N number of turns.
Q.13 A train is moving in the North-South direction with a speed of 72 km/hr. Find the amount of emf generated between two wheels, if the length of axle be 2m. Assume that the vertical component of earth’s field is 8x10-5wbm-2.
Q.14 What is the basic principle of Lenz’s Law, explain how it follow law of conservation of energy.
Q.15 What do you understand by Inductance and derive the expression for energy stored in an inductor.
Q.16 An a.c. generator consist of a coil of 50 turns, area 2.5m2 rotating at an angular speed of 60 rad/s in uniform magnetic field of B = 0.3 T between two fixed pole pieces. Given R = 500 Ώ
(i) Find the maximum current drawn from the generator?
(ii) What will be the orientation of the coil wrt. B to have max and zero magnetic flux?    
Q.17 Monica’s mother was heating food on a gas stove. Her friend Deepti came and saw her mother heating food on the gas stove. Deepti told Monica’s mother, “Why don’t you buy a microwave oven”? Monica’s mother replied at once that she doesn’t like to use microwave oven. Monica and Deepti made it clear that microwave is not harmful for cooking food. This is an easy and safe process. Monica’s mother got convinced and ordered for a microwave oven. Monica’s mother then arranged a small party for her friends and told them the advantages of a microwave oven.
• What value was displayed by Monica and her friend?
• What value was displayed by Monica’s mother?
• What value was displayed by Monica to her friends?
                                                                                                ( Value based Question )
Q.18 Derive expression of mutual inductance of two long coaxial solenoid.
Q.19 What is motional emf. Deduce an expression for it. State Fleming's right hand rule to find the direction of induced emf.
Q.20 Describe briefly, with the help of a labelled diagram, the basic elements of an A.C.
generator. State its underlying principle. Show diagrammatically how an alternating
emf is generated by a loop of wire rotating in a magnetic field. Write the expression
for the instantaneous value of the emf induced in the rotating loop.
Physics Classes By Er.Shyam Pachori Add: C.L 81 D.D Nagar Mob: 9039803981
Prime Focus on Weak Students Time : MWF 3:30 - 5 pm

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