We will publish here the portions one cannot afford to miss while preparing for the CBSE class 12  Physics Examination

The Chapters will be posted below. On Clicking the name of the chapter a new page will open. On that page there will be a set of collected questions. On clicking the questions, the complete solution to the questions will open.

Please note that this system is under preparation. We hope to complete this within a month. The link will be activated only after completing the project.

1. ELECTROSTATICS
2. CURRENT ELECTRICITY
3. MAGNETIC EFFECTS OF CURRENT
4. ELECTROMAGNETIC INDUCTION
5. ALTERNATING CURRENT
6. ELECTROMAGNETIC WAVES
7. OPTICS
8. DUAL NATURE OF MATTER AND RADIATION
9. ATOMS AND NUCLEI
10. ELECTRONIC DEVICES
11. COMMUNICATION SYSTEMS

If you find these question easy to answer, well and good. If you don’t, please revise these portions thoroughly. These are based on just the minimum level of learning expected from a Class XII student.

1. State Gauss theorem in magnetism.
2. Define the terms retentivity and coercivity.
3. Which direction will a magnetic compass show when it is kept horizontally at the magnetic north pole of earth?
4. Determine the magnitude and direction of magnetic field to be applied in a region with a vertical electric field 1000 V/m (downwards) where a proton has to move towards east with a speed of 100 m/s without any deflection. (Disregard the presence of earth’s magnetic field.)
5. Derive expression for the force on a current carrying conductor in a uniform magnetic field.
6. Using Ampere’s circuital law, derive an expression for the magnetic field at a point due to a straight conductor carrying current.
7. The radius of the first electron orbit of a hydrogen atom is 0.5 A. The electron moves in this orbit with a uniform speed of 2.2 x 10⁶ m/s. What is the magnetic field produced at the centre of the nucleus due to the motion of this elecetron?
8. Derive the relation m_r = 1+c_m (relation between magnetic permeability and magnetic susceptibility)
9. Mention the magnetic elements of earth and define each.
10. Derive expression for the magnetic dipole moment of a revolving electron.
11. Describe the principle, construction and working of a cyclotron. Why electrons cannot be accelerated using a cyclotron?

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ANSWERS

1. Gauss theorem in magnetism states that closed surface integral of magnetic field in a closed surface is zero. That is, the net magnetic flux through a closed surface is always zero.  Mathematically,
2. Retentivity is the magnetization retained by a specimen when the magnetizing field is zero. Coercivity is the reverse magnetizing force required to completely demagnetize and specimen.
3. The compass needle will not show any particular direction as the horizontal component is zero at the magnetic poles. It can rest in any direction in which it is placed just like a non-magnetic needle.

COMMUNICATION SYSTEMS

Max. Marks :: 30 Time:: 75 minutes

1 mark questions

1. Define bandwidth of a signal.
2. Define modulation index.
3. What is the function of a modem?
4. Why is short wave band used for long distance transmission?
5. Name the type of modulation prefered for digital communication.
6. Draw diagram to represent a digital signal and an analogue signal.
7. What do you mean by sampling of signal?
8. Name the appropriate communication channel needed to send a signal of band width 100 kHz over a distance of 8 km.2 Marks Questions
9. Derive an expression for the maximum distance up to which TV signals can be transmitted using a transmitting antenna of height h.
10. Distinguish amplitude modulation and amplitude modulation.
11. Draw a block diagram of a simple amplitude modulation system and explain briefly how amplitude modulation is achieved.
12. What is the need for modulating a message signal for long distance transmission?3 marks questions
13. 5 Marks Questions

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1. State the Principle of a cyclotron
2. Calculate the range of an ammeter of resistance 24 ohms and can allow a maximum current of 500mA through its coil, when shunted by a resistance of 3 ohms.
3. Write the dimensional formula of μ0
4. Define 1 ampere as defined in SI (based on force between two straight parallel conductors of infinite length)
5. State Fleming’s left hand rule.
6. State the principle of a moving coil galvanometer
7. Why a cyclotron cannot be used to accelerate electrons.
8. Write the resistance of (a) an ideal ammeter (b) an ideal voltmeter.

   2 Marks Questions

9. Derive an expression for cyclotron frequency.
10. Write the difference between paramagnetism and ferromagnetism
11. State the factors affecting the strength of an electromagnet.
12. Calculate the magnetic moment of the electron in the ground state of hydrogen atom.

    3 marks questions

13. State Ampere’s circuital law and apply it to find the magnetic field inside a torroid.
14. Discuss the equivalence of a bar magnet and a current carrying solenoid.
15. What are the magnetic elements of earth. Define each.

    5 Marks Questions

16. State Biot Savart law and apply it to find the magnetic field at a point on the axis of a circular loop carrying current.

1. The drift velocity is of the order of a few cm/s. But when we switch on a bulb, it glows instantly. How is this possible?
2. Define internal resistance.
3. If n identical resistors are connected in series first and then in parallel, Calculate the ratio of effective resistance in series to the effective resistance in parallel.
4. Define mobility.
5. State Ohm’s law.
6. State the principle of a potentiometer.
7. Write the colour coding of a carbon resistor of resistance 18000 Ω and a tolerance 10%
8. What is a thermistor?

   2 Marks Questions

9. Deduce Ohm’s law using the concept of drift velocity.
10. State Kirchhoff’s laws for electric networks.
11. Distinguish emf and terminal voltage.
12. Derive an expression for drift velocity.

    3 marks questions

13. A battery om emf E and internal resistance r gives a current 0.5 A with an external resistance of 12 Ω and a current 0.25 A with an external resistance of 25Ω. Calculate the internal resistance and emf of the cell.
14. An electric motor operating on a 50 V dc supply draws a current of 12A. If the efficiency of the motor is 30%, estimate the resistance of the windings of the motor.
15. Draw the diagram showing the experimental arrangement for determining the resistance of a given wire of unknown resistance.

    5 Marks Questions

16. (a)Explain how a potentiometer is used to determine the internal resistance of a primary cell.

    (b)State the factors affecting the internal resistance of a cell