# NCERT SOLUTIONS FOR CLASS 12 PHYSICS

PHYSICS

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“IN SCIENCE THERE IS ONLY PHYSICS ALL THE REST IS STAMP COLLECTING”

-LORD KELVIN

CHAPTERS

CHAPTER 1  Electric Charges and Fields

All folks have experienced seeing a spark or hearing a crackle once we initiate our synthetic clothes or sweater, particularly in dry weather. this can be almost inevitable with ladies garments like saree. Another common example of electrical discharge is that the lightning that we see within the sky. the rationale for these experiences is due to the discharge of electrical charges through our body, which was accumulated thanks to rubbing of insulating surfaces. you have got also heard that this is often because of the generation of electricity. Static means thing that doesn’t move or change with time. Electrostatics deals with the study of forces, fields, and potentials happening thanks to static charges.

CHAPTER 2 Electrostatic Potential and Capacitance

When an external force does work in taking a body from one point to another against a force like spring force or gravitational force, that work gets stored as the potential energy of that body. When that external force is removed, the body moves, gaining kinetic energy and losing an equal amount of potential energy. The sum of kinetic and potential energies is hence conserved. Forces of these kinds are called conservative forces. Spring force and gravitational force are examples of conservative forces. Coulomb force between two (stationary) charges is too a conservative force.

CHAPTER 3 CURRENT ELECTRICITY

Charges in motion constitute the electric current. Such currents occur naturally in most situations. Lightning is one such example  in which charges flow from the clouds to the earth through the atmosphere, sometimes with disastrous results. The flow of charges in lightning isn’t steady, but in our everyday life, we see many devices where charges flow in a steady manner, like water flowing smoothly in a river. A torch and a cell-driven clock are examples of such devices.

CHAPTER 4 MOVING CHARGES AND MAGNETISM

In this chapter, it is explained how magnetic field exerts forces on moving charged particles, like electrons, protons, and current-carrying wires. We shall also learn how currents produce magnetic fields. We will see how particles can be accelerated to very high energies in a cyclotron. We will study how currents and voltages are detected by a galvanometer. In this and subsequent Chapter on magnetism, we adopt the following convention: A current or a field (electric or magnetic)coming out of the plane or  the paper is depicted by a dot. A current or a field going into the plane or the paper is depicted by a cross.

CHAPTER 5 MAGNETISM AND MATTER

In the previous chapter,we learned that moving charges or electric currents produce magnetic fields. In the present chapter, we will  take a look at magnetism as a subject in its own right. The earth always behaves as a magnet with the magnetic field pointing approximately from the geographic south to the north. When a bar magnet is freely suspended, it’s needle point in the north-south direction. The tip which points towards the geographic north is called the north pole and the tip which points towarrds the geographic south is called the south pole of the magnet.

CHAPTER 6 ELECTROMAGNETIC INDUCTION

The phenomenon of electromagnetic induction is not only theoretical or academic interest but also of practical utility. Let us Imagine a world where there is no electricity – no electric lights, no trains, no telephones, and no personal computers. The interesting experiments of Faraday and Henry have led directly to the development of modern-day generators and transformers. Today’s civilization owes its progress to a great extent to the discovery of electromagnetic induction.

CHAPTER 7 ALTERNATING CURRENT

The electric mains supply in our homes and offices are voltage that varies like a sine function with time. Such a voltage is called alternating voltage (ac voltage) and the current driven by it in a circuit is called the alternating current (ac current)*. Most of the electrical devices we use today requires ac voltage. This is mainly because most of the electrical energy sold by power companies is distributed as alternating current. The main reason for preferring use of ac voltage over dc voltage is that ac voltages can be easily and efficiently converted from one voltage to the other by means of transformers. Further, electrical energy can also be transmitted economically over long distances. AC circuits exhibit characteristics which are exploited in many devices of daily use. For example, whenever we tune our radio to a favorite station, we are taking advantage of a special property of ac circuits – one of many that you will study in this chapter.

CHAPTER 8 EM WAVES

We learned that an electric current produces the magnetic field and that two current-carrying wires exert a magnetic force on each other. Also, we have seen that a magnetic field changing with time gives rise to an electric field. James Clerk Maxwell (1831-1879), argued that this was indeed the case – not only electric current but also a time-varying electric field generates a magnetic field. While applying the Ampere’s circuital law to find a magnetic field at a point outside a capacitor connected to a time-varying current, Maxwell noticed an inconsistency in the Ampere’s circuital law. He suggested the existence of an additional current, called by him, the displacement current to remove this inconsistency.

CHAPTER 9 RAY OPTICS AND OPTICAL INSTRUMENTS

In this chapter, we consider the phenomena of reflection, refraction, and dispersion of light, using the ray picture of light. Using the basic laws of reflection and refraction, we shall study the image formation by plane and spherical reflecting and refracting surfaces. We then go on to describe the construction and working of some important optical instruments, including the human eye.

CHAPTER 10 WAVE OPTICS

In this chapter, we are going to first discuss the initial formulation of the Huygens principle and derive the laws of reflection and refraction. we’ll also discuss the phenomenon of interference which is predicated on the principle of superposition. and that we will discuss the phenomenon of diffraction which relies on HuygensFresnel principle. Finally, we’ll discuss the phenomenon of polarisation which relies on the actual fact that the sunshine waves are transverse electromagnetic waves.

CHAPTER 11 DUAL NATURE OF RADIATION AND MATTER

It was found that certain metals, when irradiated by UV, emitted charged particles having small speeds. Also, certain metals when heated to hot temperature were found to emit charged particles. the worth of e/m of those particles was found to be the identical as that for ray particles. These observations thus established that each one these particles, although produced under different conditions, were identical in nature. J. J. Thomson, in 1897, named these particles like electrons and suggested that they were fundamental, universal constituents of matter.It was found that certain metals, when irradiated by ultraviolet, emitted charged particles having small speeds. Also, certain metals when heated to warmth were found to emit charged particles. the worth of e/m of those particles was found to be the identical as that for ray particles. These observations thus established that each one these particles, although produced under different conditions, were identical in nature. J. J. Thomson, in 1897, named these particles like electrons and suggested that they were fundamental, universal constituents of matter.

CHAPTER 12 ATOMS

Rutherford’s nuclear model was a major step towards how we see the atom today. However, it could not explain why atoms do emit light of only discrete wavelengths. How could an atom as simple as hydrogen, consisting of a single electron and a single proton, emit a complex spectrum of specific wavelengths? In the classical picture of an atom, the electron revolves around the nucleus much like the way a planet revolves around the sun. However, we shall see that there are some serious difficulties in accepting such a model.

CHAPTER 13 NUCLEI

We have learnt in previous chapter that in every atom, the positive charge and mass are densely concentrated at the centre of the atom forming its nucleus. The overall dimensions of the nucleus are much smaller than those of an atom. Experiments based on the scattering of α-particles demonstrated that the radius of a nucleus was smaller than the radius of an atom by a factor of about 104. This means the volume of a nucleus is about 10-12 times the volume of the atom. In other words, an atom is almost empty. If an atom is zoomed to the size of a classroom, the nucleus would be of the size of a head of pin.

CHAPTER 14 SEMICONDUCTOR

In this chapter, we will learn the basic concepts of semiconductor in physics and discuss some of important semiconductor devices like junction diodes (a 2-electrode device) and bipolar junction transistor (a 3-electrode device). A few circuits illustrating their applications will also be described.

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