# Class 12 Physics Most Important Topics & Questions

Class 12 Physics most important topics & questions: Physics subject is one of the highest scoring and toughest papers for class 12th. Many students confused about, how to score better marks in Physics subjects.

As of last year experts says most of the questions in the Physics subjects exams have been asked from the NCERT textbook and previous years questions bank. Therefore, students are advised to prepare only from the NCERT Book and refer to the question paper of previous year. If you do this much, then you can complete exam through good marks.

More students get Physics as a disgusting subject, but you do not know that every year the maximum marks in the Board exam comes from the subject of Physics.

## List of Class 12 Physics Most Important Topics

CBSE Board class 12th examination will probably start in the last month of February and the Physics subject examination is held in the month of March. So let’s talk about class 12 Physics most important topics.

CBSE Board class 12th Physics subject has a huge syllabus and it divided in to total 9 units and 14 chapters.

### Chapter1. Electric Charges and Fields

• Coulomb’s law
• Forces between multiple charges
• Electric field due to system of charges
• Electric field at a point on the axial line and equatorial line due to electric dipole
• Electric flux and Gauss’ theorem application

#### Important Questions:

1. Define dipole moment of an electric dipole. Is it a scalar or a vector quantity? Deduce an expression for the electric field at a point on the equatorial plane of an electric dipole of length 2 a.
1. In which orientation, a dipole placed in a uniform electric field is in (i) stable equilibrium (ii) unstable equilibrium?
1. If the radius of the Gussain surface enclosing a charge is halved, how does the electric flux through the Gaussian surface change?
1. Define electric flux. Write it’s SI unit. Explain Gauss theorem and it’s application.
1. Using Gauss’s law, deduce the expression for the electric field due to uniformly charged spherical conducting shell of radius R at a point (i) outside the shell (ii) inside the shell. Plot a graph showing variation of electric field as a function of r<R and r>R. r being the distance from the centre of the shell).

### Chapter2. Electrostatic Potential and Capacitance

• Potential due to a Point Charge
• Equipotential Surfaces
• Dielectrics and Polarization
• Combination of Capacitors
• Energy stored in a capacitor

#### Important Questions:

1. Define the dielectric constant of a medium. What is its unit?
1. What is the geometrical shape of equipotential surfaces due to a single isolated charge?
1. Draw the equipotential surfaces due to an electric dipole and write two characteristics of equipotential surfaces.
1. Derive the expression for the capacitance of a parallel plate capacitor having plate area A and plate separation d.
1. A parallel plate capacitor is charged to a potential difference V by a DC source. The capacitor is then disconnected from the source. If the distance between the plates is doubled, state with reason, how the following will charge? (i) Electric field between the plates (ii) Capacitance (iii) Energy stored in the capacitor.

### Chapter3. Current Electricity

• Ohm’s Law
• Limitations of ohm’s law
• Expression for drift velocity
• Combination of resistors
• Combination of cell
• Kirchhoff’s law
• Potentiometer and its application
• Meter Bridge

#### Important Questions:

1. Show variation of resistivity of copper as a function of temperature in graph.
1. Using the concept of drift velocity of charge carriers in a conductor, deduce the relationship between current density and resistivity of the conductor.
1. (i) State of Kirchhoff’s rules. (ii) A battery of 10 V and negligible internal resistance is connected across of the diagonally opposite corners of a cubical network consisting of 12 resistors each of 1 ohm’s resistance. Use Kirchoff’s rules to determine (a) the equivalent resistance of the network and (b) the total current in the network.
1. Draw the circuit diagram of a potentiometer which can be used to determine the internal resistance r of a given cell of emf E and explain it. How can we increase the sensitivity of a potentiometer?
1. (i) State the principle of a potentiometer. Draw a circuit diagram to compare emf of two cells. Derive the formula used. (ii) State with the help of a circuit diagram, the working principal of a meter bridge. Obtain the expression used for determining the unknown resistance.

### Chapter4. Moving Charges and Magnetism

• Applications of Ampere’s Circuital Law
• Lorentz force and Cyclotron
• Magnetic force and Torque between two Parallel Currents
• Moving coil Galvanometer into an Ammeter & Voltmeter

#### Important Questions:

1. (i)Use Biot-Savart’s law to drive the expression for the magnetic field on the axis of a current carrying circular loop of radius R. (ii) Draw the magnetic field lines due to a current carrying loop.
1. Using Ampere’s circuit al law, ibrahim the expression for the magnetic field due to a long solenoid at a point inside the solenoid at a point inside the solenoid on its axis.
1. Draw a schematic sketch of cyclotron. Explain briefly how it works and how it is used to acceder ate the charge particles? (i) Show the time period of ions in a cyclotron is independent of both the speed and radius of circular path.
1. Draw a labelled diagram and principle of a moving coil galvanometer and explain its working. What is the function of radial magnetic field inside the coil?
1. Why is it that while using a moving coil galvanometer as a voltmeter, a high resistance in series is required whereas in an ammeter a shuny is used?

### Chapter5. Magnetism and Matter

• Bar Magnet as an equivalent Solenoid
• Magnetic Dipole an Magnetic Field Lines
• Earth as a Magnet
• Properties of Diamagnetism, Paramagnetism, Feromagnetism Substances
• Permanent Magnets and Electromagnets

#### Important Questions:

1. Show diagrammatically the behaviour of magnetic field lines in the presence of paramagnetic and diamagnetic.
1. Name the properties of a magnetic material that makes it suitable for making (a) a permanent magnet and (b) a core of an electromagnet.

Best Method to Letter Writing Format in English

Best Method to Notice Writing Format & Topic for class 12th

1. The horizontal component of the earth’s magnetic field at a place equals to its vertical component there. Find the value of the angle of dip at that place.
1. Give two points to distinguish between a paramagnetic and diamagnetic substance.
1. Give two points distinguish between a diamagnetic and ferromagnetic substance with examples.

### Chapter6. Electromagnetic Induction

• Magnetic Flux
• Electromagnetic Induction and Lenz’s Laws
• Self inductance and mutual inductance
• Motional EMF or Induced EMF
• AC Generator

#### Important Questions:

1. State the Faraday’s law of electromagnetic induction.
1. Derive the expression for the induced emf and the current in the rod.
1. Define the term self-inductance of a coil. Write it’s SI unit.
1. Two concentric circular coils, one of small radius r and the other of large radius R, such that R>>r, are placed coaxially with centres coinciding. Obtain the mutual inductance of the arrangement.
1. Define the term self-inductance of a solenoid. Obtain the expression for the magnetic energy stored in an indicator of self-inductance L to build up a current I through it.

### Chapter7. Alternating Current

• Peak and RMS value of alternating Current/ Voltage
• L-C-R, L-R, L-C Series Circuit
• Resonance Power in AC Circuits
• Transformer

#### Important Questions:

1. Define the term rms value of the current. How is it’s related to the peak value?
1. A series L-C-R circuit is connected to an AC source. Using the phasor diagram, derive the expression for the impedance of the circuit. Plot a graph to show the variation of current with frequency of the source, explaining nature of its variation.
1. An alternating voltage given by V=140 sin 314t is connected across a pure resistor of 50Ώ. Find (i) the frequency of the source. (ii) The rms current through the resistor.
1. Calculate the quality factor of a series L-C-R circuit with L= 2.0 H, C= 2μF and R= 10 Ώ. Mention the significance of quality factor in L-C-R circuit.
1. An AC voltage V = Vᴑ sin ῳt is applied across a pure inductor L. Obtain an expression for the current I in the circuit and hence obtain the inductive reactance of the circuit.

### Chapter8. Electromagnetic Waves

• Displacement Current
• Oscillating electric and Magnetic fields
• Electromagnetic Waves
• Electromagnetic spectrum

#### Important Questions:

1. How are the magnitude of the electric and magnetic fields repeated to velocity of the electromagnetic waves?
1. How are X-rays, infrared and microwaves produced? Write their two important uses.
1. Give one uses of each of the following. (a) Microwaves (b) Ultraviolet rays (c) Infrared rays (d) y-rays.
1. Identify the different types of electromagnetic radiations, which are used to kill germs and, for physical therapy.
1. The small ozone layer on top of the stratosphere is crucial for human survival. why?

### Chapter9. Ray Optics and Optical Instruments

• Total Internal Reflection
• Image formation by Spherical Mirrors
• Power and combination of thin lenses
• Refraction of light through a Prism
• Scattering of light (Blue colour of sky and reddish appearance of the sun at sunrise and sunset)
• Optical Instrument: Microscopes and astronomical telescopes

#### Important Questions:

1. State the criteria for the phenomenon of total internal reflection of light to take place.
1. Draw a ray diagram of reflecting type telescope. State two advantages of this telescope over a refracting telescope.
1. Define the revolving power of a telescope. Write any two advantages of a reflecting telescope over a refracting telescope.
1. Draw a labelled ray diagram showing the formation of a final image by a compound microscope at least distance of distinct vision.
1. Draw a labelled ray diagram to obtain the real image formed by an astronomical telescope in normal adjustment position. Define it’s magnifying power.

### Chapter10. Wave Optics

• Wave fronts
• Refraction and Reflection of Plane Waves using Huygens Principle
• Interference of Light Waves
• Diffraction of light
• Polarisation

#### Important Questions:

1. Define a wavefront. Using Huygen’s principle showing how a plane wave gets refracted when it is incident on the surface separating a rarer medium from a denser medium? Hence, verify Snell’s laws of refraction.
1. In Young’s slit experiment, deduce the conditions for constructive and destructive interference. Hence, write the expression for the distance between two consecutive bright or dark fringe.
1. Compare the interference pattern observed in Young’s double slit experiment with single slit diffraction pattern, pointing out two distinguishing features.
1. Define a linearly polarised or plane polarised light. Why is the phenomenon of polarisation not observed by sound waves?
1. What is linearly polarised light? Describe briefly using a diagram how sunlight is polarised.

### Chapter11. Dual Nature of Radiation and Matter

• Experimental Study of Photoelectric Effect
• Einstein’s Photoelectric equation: Energy Quantum of Radiation
• de Broglie Hypothesis
• Davisson-Germer Experiment
• Laws of Photoelectric Emission

#### Important Questions:

1. Define intensity of radiation on the basis of photon picture of light. Write it’s SI unit.
1. State the variation of photoelectric current with collector plate potential for different intensities but same frequency of incident radiation.
1. Write Einstein’s photoelectric equation. State clearly the three salient features observed in photoelectric effect which can be explained on the basis of above equation.
1. Define the terms threshold frequency and stopping potential.
1. Derive an expression for the de-Broglie wavelength associated with an electron accelerated through a potential V. Draw a schematic diagram of a localised wave describing the wave nature of the moving electron.

### Chapter12. Atoms

• Alpha-particle scattering experiment by Rutherford
• Bohr’s Model of Hydrogen Atom
• Energy Level Diagram
• Limitations of Bohr’s Model

#### Important Questions:

1. The ground state energy of hydrogen atom is -13.6 eV. What are the kinetic and potential energies of electron in this state?
1. State Bohr’s postulate of hydrogen atom that gives the relationship for the frequency of emitted photon in a transition.
1. Using Bohr’s postulates, obtain the expression for the total energy of the electrons in the stationary states of the hydrogen atom. Hence, draw the energy level diagram showing how the line spectra corresponding to Balmer series occur due to transition between energy levels.
1. Draw a schematic arrangement of the Geiger-Marsden experiment. How did the scattering of alpha particles by a thin foil of gold provide an important way to determine an upper limit on the size of nucleus? Explain briefly.
1. Which transition corresponds to emission of radiation of maximum wavelength?

### Chapter13. Nuclei

• Nuclear binding energy
• Nuclear Force
• Nuclear fission and nuclear fusion

#### Important Questions:

1. Define the terms (a) half-life (b) average life. Find out the relationship with the decay constant (ʎ).
1. State the law of radioactive decay. Plot a graph showing the number N of undecayed nuclei as a function of time t for a given radioactive sample having half-life T1/2. Depict in the plot, the number of undecayed nuclei at (i) t = 3 T1/2 (ii) t = 5T1/2
1. Distinguish between nuclear fission and fusion. Show how in both these processes energy is released. (i) Write three properties of nuclear force.
1. Draw a plot BE/A versus mass number A for 2 ≤ A ≥ 170. Use this graph to explain the release of energy in the process of nuclear fusion of two light nuclei.
1. Draw a plot of a potential energy of a pair of nucleons as a function of their separations. Mark the regions where the nuclear force is (i) attractive and (ii) repulsive.

### Chapter14. Semiconductor Electronics: Materials, Devices and Simple Circuits

• Semiconductor diode: I-V characteristics in forward bias and reverse bias
• Diode as a rectifier; Special Purpose
• p-n Junction diode in forward bias and reverse bias
• Zener Diode as a voltage regulator
• Transistor as an amplifier

#### Important Questions:

1. With the help of a suitable diagram, explain the formation of depletion region in a p-n junction. How does it’s width change when the junction is (i) forward biased and (ii) reverse biased?
1. Why is a Zener diode considered as a special purpose semiconductor diode? Draw the I-V characteristics of Zener diode and explain briefly, how reverse current suddenly increase at the breakdown voltage?
1. The output of a 2-input AND gate is fed to a NOT gate. Give the name of the combination and it’s logic symbol. Write down it’s truth table.
1. Draw a circuit diagram of a CE transistor amplifier. Briefly explain it’s working and write the expression for (i) current gain (ii) voltage gain of the amplifier.
1. Give the circuit diagram of a common-emitter amplifier using n-p-n transistor. Draw the input and output waveforms of the signal. Write the expression for its voltage gain.

#### Conclusion

The entire given “CBSE Class 12 most important topics & questions” are necessary for CBSE class 12th exam. Student does not miss all these class 12 physics most important topics and questions.

If you have aggregate just passed marks in the examination, you can ignore it. But you will have aggregates good marks in the exams, and then understand these topics and questions. You will be definitely aggregates the Ace number.