class 12 physics Conceptual questions in EMI

 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 induced current will be large

5. How does the self inductance of a coil change when an iron rod is introduced in it?

Iron has a large relative permeability. It increases the magnetic flux and so the self inductance of the coil also increases.

6. Why is spark produced in the switch of a fan when it is switched off? .

The break of circuit is sudden.  A large induced emf is set up across the gap in the switch and thus spark occurs.

7. A lamp connected in parallel with a large inductor glows brilliantly before going off when the switch is put off. why?

A very large induced emf is set up when the circuit breaks.  This makes the bulb glow brilliantly before going off.

8. Self inductance is called the inertia of electricity. Why?

Self induction  is the property by which it tends to maintain the magnetic flux linked with it and opposes any change in the flux by inducing current in it.  This is similar to inertia.

9. When is the magnetic flux crossing a given surface area held in a magnetic field maximum?

When area is held perpendicular to the direction of the magnetic field.

10. A wire cuts across a flux of 0.2 x 10  Wb in 0.12 seconds. Find the emf induced in the wire.




11. A bicycle generator creates  3 V when the bicycle is travelling at a speed of 9 km/h.  How much emf is generated when the bicycle is travelling at a speed of 15 km/h?




12. State the law that gives the polarity of the induced emf.

Lenz's law states that the direction of induced current is such that it opposes the cause which produces it.

13. Show that the SI unit of inductance, henry is equal to volt second per ampere.



14. When a current in a coil changes with time, how is the back emf induced in the coil related to it?

Back emf induced = Rate of change of current



15. Mention the methods of generating induced emf.

1. Changing the magnetic field B
2. Changing the area a of the coil
3. Changing the relative orientation θ of B and A.

Refer textbook for the following questions:

16. Define:

EMI
Motional emf
Self induction
Mutual induction

17. State  

Faraday's laws of EMI
Lenz's law
Flemings right hand rule

18. Write the formula for

Magnetic flux
Induced emf
Average induced emf
Induced current
Motional emf

Maximum induced emf
Maximum induced current

Flux for self induction
Self induced emf
Flux for mutual induction
Mutual induced emf
Self inductance of a long solenoid
Mutual inductance of two closely wound solenoids

       

Comments

Post a Comment

Popular posts from this blog

CBSE CLASS 12 PHYSICS NUMERICALS (SOLVED)

Image
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...
Read more

CLASS 10 SCIENCE Short and Very short Answers

Class 10 Students can go through this as a ready reckoner for their Science Board Examination  All answers are given in blue 1. What happens when Silver chloride is put under sunlight? Silver metal and chlorine gas are formed . 2. Acid used in refining of petroleum to remove sulphur and other compounds Sulphuric acid 3. The magnetic field lines de to straight wire carrying a current are ___ Circular: Concentric circles with centre at the axis of the conductor. 4. When more than one resistors are in series, the quantity that remains same in them is ________ Current:  Resistors in series have same current 5. The percentage of solar radiation absorbed by all the green plants for the process of photosynthesis is about _________ 1 percent : The green plants convert this into food energy and make this energy available to the rest of the ecosystem. 6. The property of a proton that can change while it moves freely in a magnetic field Momentum When a proton moves in a magnetic field, i...
Read more

CLASS 12 PHYSICS ONE MARK QUESTIONS WITH ANSWERS

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....
Read more