# Part III Applied Science

## Magnetic Keepers, magnetic lines of force and their properties. Plotting the lines of force Terrestriel magnetism

Magnetic keepers A magnet keeper, also known historically as an armature, is a ferromagnetic bar made from soft iron or steel, which is placed across the poles of a permanent magnet to help preserve the strength of the magnet by completing the magnetic circuit; it is important for magnets that have a low magnetic coercivity, such as Alnico magnets. Keepers also have a useful safety function, as they stop external metal being attracted to the magnet.Â  Most magnets do not need a keeper, only those with low coercivity, meaning that they are easily susceptible to stray fields.Â  Magnet can be ... Read more

## determination of focal length of concave miror by single pin method. [Relation between u-v-f [numerical examples]

Determination of focal length of concave miror by single pin method. [Relation between u-v-f (numerical examples) Spherical mirrors It is a mirror which has the shape of a piece cut out of a spherical surface. Two types of spherical mirrors are; Concave mirror: Its inner concave surface reflects, and has polished outer surface. Convex mirror: Its outer convex surface reflects, and has polished inner surface. Pole (P): The centre of the spherical mirror. Centre of curvature (C): The centre of the sphere, of which the mirror is a part. Principal focus (F): The point on the principal axis, on which ... Read more

## General studies of alternating current and direct current

General studies of alternating current and direct current Alternating Current Alternating Current (AC) Alternating current describes the flow of charge that changes direction periodically. As a result, the voltage level also reverses along with the current. AC is used to deliver power to houses, office buildings, etc. AC can be produced using a device called an alternator. This device is a special type of electrical generator designed to produce alternating current. A loop of wire is spun inside of a magnetic field, which induces a current along the wire. The rotation of the wire can come from any number of ... Read more

## electro magnetic induction, electric motor

Electro magnetic induction When a DC current passes through a long straight conductor a magnetising force, H and a static magnetic field, B is developed around it If the wire is then wound into a coil, the magnetic field is greatly intensified producing a static magnetic field around itself forming the shape of a bar magnet giving a distinct North and South pole. The magnetic flux developed around the coil being proportional to the amount of current flowing in the coils windings as shown. If additional layers of wire are wound upon the same coil with the same current flowing ... Read more

## Thermal effect of current itâ€™s use, calculation of power and electrical energy

Thermal effect of current itâ€™s use, calculation of power and electrical energy Spent When an electric current flows through a conductor, electrical energy is expended n over coming the frictional resistance between eh electrons and the molecules of the wire. If potential difference of V volts is applied across a conductor and current of I amperes flows through it for time of t seconds, then energy expended will be equal to VIt watt-secs or joules. If R is the resistance of the conductor through which a current of I amperes flows and V is the potential difference applied across its ... Read more

## Electricity and its effects -electric intensity, potential, potential difference

Electricity and its effects -electric intensity, potential, potential difference Electricity is the physical flow of electrons, referred to as an electrical current. Electricity is an energy carrier that efficiently delivers the energy found in primary sources to end users, who in turn convert it into energy services. Electricity can be created in three ways: The most common is through electro-magnetic conversion, where electricity is generated by moving an electric conductor, such as a wire, inside a magnetic field. The most practical example of this method is a generator connected to a turbine. The turbine provides the motion required to move ... Read more

## Primary and secondary cells their properties and drawback

Primary and secondary cells their properties and drawback Primary Cell Primary cells are those that cannot be recharged and needs to be discarded after the expiration of their lifetime. If the electrolyte is not in liquid form, we are talking about dry cells. Primary cells usually have high energy density, capacity, are slowly to discharge, easy to use and not excessively expensive. Alkaline are probably most commonly used primary batteries.Â  They usually have zinc anode, carbon cathode and electrolyte. The voltage curve for discharging alkaline batteries is very steep (almost linear. When the battery empties, its voltage drops almost linearly. ... Read more

## Electric discharge in gases, discharge tube, cathode rays, X-rays and their properties

Electric discharge in gases Electrical discharge through gases is studied by using a specially designed glass tube commonly called as a discharge tube. It consists of a cylindrical glass tube having a side tube, and two metallic electrodes one at each end. These electrodes can be connected to the respective terminals of a high tension power supply. Air from inside the tube can be pumped out by connecting the side tube to a vacuum pump, and a desired pressure can be maintained inside the tube. It was found that gases could not conduct electricity even when an electrical potential of ... Read more

## Working principle and use of generator

working principle and use of generator Generator is a machine that converts mechanical energy into electrical energy. It works based on principle of faraday law of electromagnetic induction. The faradays law states that whenever a conductor is placed in a varying magnetic field, EMF is induced and this induced EMF is equal to the rate of change of flux linkages. This EMF can be generated when there is either relative space or relative time variation between the conductor and magnetic field. Working of Generators Generators are basically coils of electric conductors, normally copper wire, that are tightly wound onto a ... Read more

## Simple telescope and astronomical telescope, Construction working, uses, ray diagram

Simple telescope and astronomical telescope, Construction working, uses, ray diagram Simple telescope A simple working telescope requires nothing more than a pair of lenses mounted in a tube. The lens in front, known as the objective, focuses an image; the lens in back, known as the eyepiece, magnifies the image. Although it may seem like a crude device, a simple telescope nicely illustrates the basic working principles of more powerful astronomical instruments. LENSES Light normally moves in straight lines, but there are situations in which this is not true. You are already familiar with some: for example, the distortions you ... Read more