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  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....

  QUESTIONS/SUMS BASED ON IMPORTANT CONCEPTS 1. Define Electronic device. State its two basic types. 2. Classify solids on the basis of their values of electrical conductivity and resistivity. 3. Classify semiconductors on the basis of their chemical composition. Give some examples of each. 4. Classify semiconductors on the basis of the source and the nature of the charge carriers. 5. Describe the mechanism of conduction in intrinsic semiconductors on the basis of valence bond model. 6. How do holes act as positive charge carriers? 7. Mention the limitations of intrinsic semiconductors. 8. What is doping? 9. What are the requisites of doping? 10. Mention the two types of dopants. 11.  Mention the various methods of doping. 12.  Mention the two types of extrinsic semiconductors. 13. Define 1. Valence band 2. Conduction band 3. Energy band 14. Distinguish between intrinsic and extrinsic semiconductors . 15. Distinguish between n-type and p-type semiconductors. 16. Write the...

 CLASS 12 PHYSICS   QUESTIONS/SUMS BASED ON IMPORTANT CONCEPTS (Refer text for answers) 1 Describe Thomson's Model of an atom. 2 Describe Rutherford's experiment on the scattering of alpha particles by a nucleus.  Explain the observations and conclusions of the experiment 3. Define Distance of closest approach Impact Parameter 4. Name the first atom model. 5. Name the experiment responsible for the discovery of atomic nucleus. 6. On what factors does the shape of trajectory of scattered alpha particles depend? 7. Write the formulae for 1. KE of alpha particle 2. Distance of closest approach 3. Impact Parameter  8. Mention the limitations of Rutherford's atomic model. 9. What is the distance of closest approach when a 5 MeV proton approaches a gold nucleus? 10. In a Geiger Marsden experiment, what is the distance of closest approach to the nucleus of a 7.7 MeV alpha particle before it comes momentarily to rest and reverses its direction. 11. Find the impact parameter...

    Questions/Sums on Important Concepts   Hi students,  just 9 days left for CBSE Class 12 Physics Board Exam 2025. So as a ready reckoner, I have given the answers to some of the questions here.  For derivations and graphs, please refer your textbook.                    1. Why do metals have a large number of electrons? In metals, the electrons in the outermost shells are loosely bound to the nucleus. Thus there are a large number of free electrons moving in a random manner inside the metals at room temperature. 2. Define work function of a metal. The minimum amount of energy required by an electron to just escape from the metal surface. 3. Name the different types of electron emission. Thermionic emission Field emission P hotoelectric emission Secondary emission 4. Draw the graph of effect of intensity of light on photoelectric current. Refer textbook. 5. Define Stopping potential. The value of the retarding p...

  CLASS 9 POLYNOMIALS  ASSIGNMENT  Factorise the following: 1. 2x 2  + 7x + 6 2. a 2  + 7a +10  3. x 2  – x – 6 4. t 2  – 5t – 14 5. 3y 2  + 2y – 8  6 . Find whether x-1 is a factor of  x 4  + 3x 3  – x – 3. 7. Find whether x+1 is a factor of x 3  + x 2  – 5x + 3 8. Find the values of the polynomial 3x 4  + 6x 3  – 12x 2  – 24x at x=-2, 3.  9. Evaluate 4x 4  + 14x 3  + 8x 2  – 8x at x = 1/4, -1/2. 10. Factorise y 3  + 2y 2  – 4y – 8 11. Factorise  2t 3  + 7t 2  + 4t – 4   12. Factorise m 3 – 3m 2 – 9m – 5