A current is any motion of charge from one region to another. The illustration below shows two bodies at different potentials. When these are connected with a wire, free electrons flow from B to A until both bodies attain the same potential, after which the current ceases to flow. Current flows if a potential difference exists throughout a conductor. This branch of physics dealing with charges in motion is called current electricity.
The amount of charge flowing through a given cross-section of a conductor per unit time constitutes electric current.
When a battery or a cell is connected across the ends of a conductor, the direction thus set up exerts a force on the free
electron causing them to move as shown in the figure. The arrows give the direction of the conventional current.
The electrons do indeed flow.When the circuit is closed, an electric field is set up in the entire wire from the generating plant to the user and back again on another wire -- a closed circuit is required!A wire is a
conductor precisely because some of the electrons are free to move when pushed by an electric field.
The closed circuit is required so the electrons can flow in a closed circuit; no electrons are lost!
Electricity is one of the most important sources of energy. Lights, fans, motors, radios and television are some common appliances which work on electricity. In general usage, the word "electricity" is adequate to refer to a number of physical effects. In scientific usage, however, the term is vague, and these related, but distinct, concepts are better identified by more precise terms.
It can also define as, Electricity is a form of energy produced by the movement of electrons. Electricity is electrical power or an electric current. This form of energy can be sent through wires in a flow of tiny particles. It is used to produce light and heat and to run motors.
The word'electric' is derived from the Greek word 'elektron' meaning amber. The existences of charges were known when charged particles were produced by rubbing (due to friction) of suitable materials. These facts are demonstrated by simple experiments.
a) uspend a glass rod rubbed with silk. Bring another glass rod rubbed with silk nearer to the suspended rod. It is observed that, the suspended rod will swing away, showing repulsion.
b)Similarly, suspend a plastic rod rubbed with fur and bring another plastic rod rubbed with fur closer to it, we observe that the rods repel.
c)Again, if we suspend a glass rod rubbed with silk and bring a plastic rod rubbed with fur nearer to the glass rod, we observe that the rods attract.
From the above, we find that glass rod rubbed with silk acquire 'something' different from that of plastic rubbed with fur. That 'something' is called 'charge'.
To know about the electric charges we must know the structure of atom.It was discovered in 1911, by Rutherford performed by Hans Geiger and Earnest Marsden, under the direction of Rutherford that an atom is made up from the protons and neutrons in the nucleus, with a very small contribution from the or biting electrons
An atom consists of nucleus centrallyplaced with protons consisting positive charge. They seem to be surrounded by a kind of invisible force field.
This is called a a electrostatic field
The neutral particles are neutrons.
The electrons are the negative charged that revolves around the nucleus.This negatively charged electrostatic field is exactly the same strength as the electrostatic field in protons.
The negative charge of an electron is the same as the positive electrical charge of the much larger in size proton. This way the atom stays electrically neutral. The value of one charge is 1.6×10−19 coulombs (+ for protons and – for electrons).
In Physics we usually call the charge as electric charge, electrostatic charge, electrical charge or simply charge. We denote it by q. +q means protons and –q means electrons.
In a neutral atom the number of protons and number of electrons are same hence it does not carry any charge. But when the number or protons and number or electrons vary then atom acquires charge. If there are fewer electrons than protons, the atom has a positive charge. The amount of charge carried by an atom is always a multiple of the elementary charges, the elementary charge is e (e = ± .6×10−19 coulombs). When an atom losses electrons than it acquires positive charge and when it gains electrons it acquires negative charge. Hence, the net charge on an atom is q = ne, where n is number or electrons lost or gained.
Thermal expansion is the tendency of matter to change in volume in response to a change in temperature. When a substance is heated, its particles begin moving and become active thus maintaining a greater average separation. Materials which contract with increasing temperature are rare; this effect is limited in size, and only occurs within limited temperature ranges. The degree of expansion divided by the change in temperature is called the material's coefficient of thermal expansion and generally varies with temperature.
It is our common experience that most substances expand on heating and contract on cooling. A change in the temperature of a body causes change in its dimensions. The increase in the dimensions of a body due to the increase in its temperature is called thermal expansion. The expansion in length is called linear expansion. The expansion in area is called area expansion. The expansion in volume is called volume expansion
A reference scale with respect to which the temperatures can be measured is known as 'scale of temperature'. Various scales of temperatures are in use. Important scales of temperature are:
Celsius scale
Fahrenheit scale
Kelvin Scale
Lower and upper fixed point of temperature
To devise a scale of temperature, fixed reference points (temperature) are required, with respect to which all other temperatures are measured. For both Celsius and Fahrenheit Scales of temperatures, the fixed points are as follows:
Lower fixed point:
Melting point of pure ice at normal atmospheric pressure is regarded as the lower fixed point.
Upper fixed point
Boiling point of pure water at normal atmospheric pressure is regarded as the lower fixed point.
Celsius Scale of TemperatureCelsius scale of temperature was devised by a Swedish astronomer Anders Celsius (1701 1744). In this scale, the lower fixed point (the temperature of melting ice at normal atmospheric pressure) is taken as zero degree Celsius, written as 00C. The upper fixed point (the temperature of pure boiling water at normal pressure of 76 cm of mercury) is considered to be hundred degree Celsius, written as 100OC. The interval between 00C and 1000C is divided into hundred equal parts. Each part represents 10C. This is a convenient scale of temperature, which is widely used.
Fahrenheit Scale of Temperature
This scale of temperature was devised by Gabriel Fahrenheit (1687-1736). The lower and upper fixed points in this scale are considered as 320F and 2120F respectively. The interval of 1800 F is divided into 180 equal parts. Each part is known as 10F. This is widely used by doctors.
