SCIENCE CAPSULES

    Consider a source of light like a candle.  The light (intensity) spread as the spherical wave .  We know  the brightness decreases as we move away from the candle.  We want to know exactly what is the intensity of the light  falling on the unit area at a particular distance from the source.  It can be obtained by dividing source's strength by the area of the sphere at that distance. Intensity on the unit area  = source's strength / area of the sphere                                         I=S/4𝚷R²                             R-Distance from source                                        I proportional  1/R²               sin...

    Water flows from mountain top to valley down.  All fluids flow from high pressure to low pressure.  Heat flows from high temperature to low temperature.  Similarly, the electrons flow from surplus point to starving point.  In chemical reactions of a battery, there are more electrons at negative electrode and there is lack of electrons at positive electrode.  Then the electrons try to flow from negative to positive electrode.  When we connect negative and positive point by a wire, the current (electrons) flow from high electric potential to low electric potential.   (Note: Electrons flow from negative to positive end and the conventional current is taken to flow from positive to negative).        Resistance:  We know the current flows through the metal wire.  The atoms in the metal are never at rest.  They vibrate due to temperature.  The electrons that move through these vibrating ato...

     We know electron whirls and spins in an atom.  When an electron revolves, the electric fields also circulates.  Consequently a magnetic field is created perpendicular to the plane of rotation(maxwell's equation).       Suppose in a loop of wire, a current (bunch of electrons) flows, a magnetic field will be created through the loop.  One side north pole and the other side south pole.  We will extend this principle further.  If we have a coil of wire (more number of loops).  The magnetic fields are added up and we get a strong magnetic field.  In short, the current carrying coil acts like a bar magnet with north pole at one end and the south pole at the other end.      Now we will do a simple experiment to demonstrate magnetism created by a coil. Wire the circuit as given below.       Here, when the switch is closed, the current flows through the coil only...

  ELECTRONS AT WORK  Electron was discovered by J.J. Thomson  more than 100 years ago.  It is said to carry negative charge and negligible mass.  It is present in all the elements      When electron flows in a conductor, it is electric current.  We know, nothing serves like electricity.       Around the moving electrons magnetic field is formed and it gives rise to electromagnet.   When the electron oscillates electromagnetic waves like radio waves are radiated.  It is used for communication purpose.     While the electrons are moving in a conductor, they collide with the atoms and produce heat.  Many heating devices are made using this principle.  In atoms, when electron jumps from higher orbit to lower orbit, it loses energy in the form of light waves, X-rays etc,.   When the electrons moves in the magnetic field  at an angle, it experiences a force called Lore...

      A motor mainly contains two components, a permanent magnet and a coil of wire.  We know that when a current is passed through the coil, a magnetic field is created. Action:      Alternating current is passed through the coil in the motor.  The direction of the current alternates frequently and hence the direction of the magnetic field created by the coil also changes.  The permanent magnet attracts or repels the coil according to the direction of the magnetic field.  Since the attraction and repulsion alternately happens, the coil begins to rotate .  This is the simplified explanation of the working of a motor.      Motor is main part in many house hold electric appliances.  For example:  hair drier, water pump, washing machine, fridge, AC, mixie, grinder, fan, vacuum cleaner and so on.      So a coil and the electromagnetic force plays the main role in  electrical engine...

   J ust a pair of metal plates separated by a small distance is called "capacitor".  It can store electric field(charges) and release it.         A coil of wire can create magnetic field when electric current is passed through it.  Magnetic field depends on the strength of the current.  A coil of conductor is called an "inductor".        Let us connect a battery for some time to the capacitor till it fully charges up.  Next we will connect the capacitor and the inductor in parallel.  Now the actions starts.        The capacitors slowly discharges, current flows in the circuit and magnetic field builds up in the coil.      When the capacitor is fully discharged, the magnetic field of the coil starts to collapse and the current flows(Faraday's law)  in the same direction.  At the same time the capacitor is charged up in the opposite direction.   ...

    Water flows in the river and finally drains into the ocean without any use.  We build a dam across it.  Water is blocked by the dam and hence water pressure rises.  The high pressure water can be used to generate electricity.      Similarly, the current (electron) flows from positive to negative terminal of a battery when they are connected.  Now, insert a resistor in the path of current.   The resistor resists the flow of electrons and builds up electrical pressure (voltage , potential)across it.  It is according to ohms law V = IR. This electrical voltage can be extracted from resistor and can be used for any purpose.      So resistors are like dams that controls the flow of current and builds up required electrical potential.  There are no circuits without resistors.