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CBSE CLASS 12 PHSICS  NUMERICALS (SOLVED)   1. A long straight wire carries a current of 35 A. What is the magnitude of the field B at a point 20 cm from the wire? 2.  What is the magnitude of magnetic force per unit length on a wire carrying a current of 8 A and making an angle of 30º with the direction of a uniform magnetic field of 0.15 T?    3. Two long and parallel straight wires, A and B, carrying currents of 8.0 A and 5.0 A in the same direction, are separated by a distance of 4.0 cm. Estimate the force on a 10 cm section of wire A. 4.  A square coil of side 10 cm consists of 20 turns and carries a current of 12 A. The coil is suspended vertically, and the normal to the plane of the coil makes an angle of 30º with the direction of a uniform horizontal magnetic field of magnitude 0.80 T. What is the magnitude of torque experienced by the coil? 5.  A short bar magnet placed with its axis at 30° with a uniform external magn...

  MAGNETIC EFFECT OF CURRENT  1. Is the source of magnetic field an analogue to the source of electric field? No. The source of electric field is an electric charge but the source of magnetic field is not a magnetic charge. 2. A current is set up in a long copper pipe.  Is there a magnetic field (i) inside (ii) outside the pipe? (i) The magnetic field is zero inside the pipe . (ii)  A finite magnetic field exists outside the pipe. 3. Why does a solenoid contract when a current is passed through it? The current in adjacent turns of the solenoid flows in the same direction. So different turns attract one another and thus the solenoid contracts. 4. Why are the pole pieces of galvanometer made concave? Concave poles produce strong, uniform and radial magnetic field. 5. What is the main function of soft iron cylinder between the poles of a galvanometer? Due to the high permeability of soft iron, the magnetic lines of force crowd through the soft iron core which increases...

  ELECTROMAGNETIC INDUCTION   Magnetic flux The magnetic flux through any surface placed in a magnetic field is the total number of magnetic lines of force crossing this surface normally. It is a scalar quantity denoted by ∅ ∅ = BAcosθ B and A are vector quantities and the direction of A is the direction of the outward drawn normal to the surface. SI unit is weber (Wb) 1. What is the cause of induced emf? The cause of induced emf is the change of magnetic flux linked with a circuit. 2. Induced emf is also called back emf.  Why? It is because induced emf always opposes any change in applied emf. 3. Predict the polarity of the plate A and B of the capacitor when a magnet is moved towards it as shown.    When North pole of the magnet is moved towards the loop, current is induced in the anticlockwise direction.  So the plate A has positive polarity and B has negative polarity. 4. The inductance coils are made of copper. Why? Copper has small resistance and so i...

ONE MARK QUESTIONS WITH ANSWERS  Hi students, I have made my best effort in this short time to post the Q&A given below.  The main aim is to help students answer one mark and also other conceptual questions with these points in mind. Kindly go through this after completely learning all chapters.   Note:  Students are advised to read all the chapters thoroughly and take points then and there.   Also note that the answers are marked in blue.   1. Coulombian force is a central and electric force. 2. An infinite number of capacitors  with capacitances 1 μF, 1/2  μF , 1/4  μF  , 1/8  μF .. etc are connected in parallel combination.  Their equivalent capacitance will be 2  μF. 3. The power of electric circuit is V²/R. 4. The radius of a circular path in which an electron will move, when subjected to a perpendicular uniform magnetic field B is mv/Be 5. Infrared  radiation causes heating effect in sunlight. 6....