Tuesday, 16 September 2014

important questions of magnetic effect and magnetism class 12


Q.1. Where on the surface of Earth is the angle of dip 90 ?
Q.2 Which material is used for making permanent magnet & why?
Q.3 An electron beam projected along +X-axis, experiences a force due to a magnetic field along the +Y-axis. What is the direction of the magnetic field?
Q.4 Why should the spring/suspension wire in a moving coil galvanometer have low torsional constant?
Q.5 Why a galvanometer cannot be used as an ammeter directly?
Q.6. How is the magnetic field inside a given solenoid made strong ?
Q.7 Write the expression for Lorentz magnetic force on a particle of charge 'q' moving with velocity V in a magnetic field B .Show that no work is done by this force on the charged particle.
Q.8 Draw magnetic field lines when a (i) diamagnetic, (ii) paramagnetic substance is placed in an external magnetic field. Which magnetic property distinguishes this behaviour of the field lines due to the two substances ?
Q.9 Derive an expression for magnetic field on the axial line of circular loop of radius ‘a’ and carrying current I at a distance x from the centre.
Q.10  Write the relation for the force  F acting on a charge carrier q moving with a Velocity V  through a magnetic field B  in vector notation. Using this relation, deduce the conditions under which this force will be (i) maximum (ii) minimum.
 Q.11 Compare hysteresis curve of soft iron and steel , which dissipate more energy and why ?
Q.12  Define the terms 'Magnetic Dip' and 'Magnetic Declination' with the help of relevant diagrams.
Q.13. What is radial magnetic field? What is its importance in a moving coil galvanometer? How is a radial magnetic field realized in moving coil galvanometers?
Q.14 An electron and a proton moving parallel to each other in the same direction with equal momenta enter into a uniform magnetic field which is at right angle to their velocities. Calculate the ratio of radii of the circular path.
Q.15. State and prove Ampere’s circuital theorem and apply it to find the magnetic field inside a solenoid .
Q.16 Obtain an expression for the magnetic moment of an electron moving with a speed ‘v’ in a circular orbit of radius ‘r’. How does this magnetic moment change when :
(i) the frequency of revolution is doubled?
(ii) the orbital radius is halved?
Q.17 Pooja went to the market with her mother and decided to come back home by metro. At Metro station they were made to pass through a gate way for security check. Pooja passed through it and was waiting for her mother to come. She heard a long beep when her mother passed through metal detector. Pooja was confused why metal detector beeped in case of her mother. She asked the duty staff, who explained her in detail. Both were satisfied with the security system.
• What values are displayed by pooja
• What is cause of sound through metal detector
• Write the Principle on which a Metal detector works
                                                                                                ( Value based Question )
Q.18 Describe the principle  and working of a cyclotron. Explain why an electron cannot be accelerated using a cyclotron , prove that time period does not depend upon speed of the particle.
Q.19 A galvanometer with a coil of resistance 120 ohm shows full scale deflection for a current of 2.5 MA. How will you convert the galvanometer into an ammeter of range 0 to 7.5 A? Determine the net resistance of the ammeter. When an ammeter is put in a circuit, does it read slightly less or more than the actual current in the original circuit? Justify your answer.                                          
Q.20 Derive an expression for the force between long straight conductors carrying current and hence define 1 ampere , what happen when direction of current reversed in one conductor.
Physics Classes By Er.Shyam Pachori add: C.L 81 D.D Nagar                           Mob.: 9039803981 Batches MWF Time: 3:30 - 5 Pm 
 

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