Physics IV
Electric Charges and Field
The word 'electric' is derived from the Greek word 'elektron' meaning amber. The existence of charges were known when charged particles were produced by rubbing (due to friction) of suitable materials. These facts are demonstrated by simple experiments.
Electrostatic Potential and Capacitance
Just as the electric field is described as force per unit charge, electric potential at a point can be described as electrical potential energy per unit charge.
Current Electricity
Electric current is a means by which electrical energy is transferred from one place to another for utilisation. Charges in motion constitute an electric current.
Thermal and Chemical Effects of Currents
When a potential difference is applied across the ends of a conductor, the free electrons are accelerated and acquire kinetic energy. As the electrons move through, they collide with the positive ions and atoms of the conductor and transfer their kinetic energy to them.
Moving Charges and Magnetism
The branch of physics which deals with magnetism due to the electric current is called electromagnetism. For a long time it was hard to believe if there existed a relation between electricity and magnetism.
Magnetism and Matter
The first magnetic phenomenon observed were those associated with naturally occurring magnets, fragments of iron ore found near the ancient city of Magnesia. These attracted unmagnetised iron. The attraction was maximum at certain regions of the magnet called the poles.
Electromagnetic Induction
We have seen in the previous lesson that a current carrying conductor when kept in a magnetic field experiences forces and torques.
Alternating Currents
Do we use dry cells for operating electrical appliance? It is not impossible to tap continuous supply of energy from electrochemical cells. Electrical circuits in homes, factories and offices receive such energy form local power companies. In most countries the energy is supplied via oscillating e.m.fs and currents. These oscillating currents are called as alternating currents, shortly as a.c.
Optics
It is the phenomenon of change in the path of light without any change in medium. It is a part of a hollow sphere, whose one side is reflecting and other side is opaque.
Relation between Relative Refractive Index and Absolute Refractive Index
Let light travel from air to medium 1. If c and v1 are the velocities of light in these media, the refractive index of medium 1 with respect to air, or the absolute refractive index of medium 1.
Dual Nature of Radiation and Matter
When light of sufficiently small wavelength is incident on a metal surface, electrons are ejected from the metal. This phenomenon is called as 'photoelectric effect' and the ejected electrons are called as 'photoelectrons'.
Atoms and Nuclei
In the nineteenth century scientists saw enough evidence to prove that each element has its distinctive atom. But all tem atoms contain identical electrons. In spite of the fact that electrons carry negative charge, atoms as whole were found to be neutral.
Semiconductor Devices
In the chapter on current electricity, we had learnt about the flow of charges, conditions to produce the flow and how different materials respond to an external electric field. We had seen how materials are classified as conductors and insulators.
Communication Systems
The concept of information is central to communication. There is no precise definition of the word "information". So, instead of information, we deal with "message".
