LEARNING-CARE CENTRE: Educational materials for science students in Senior Secondary School

  ELECTRIC CELLS Cells and batteries are portable sources of electrical energy. They are used in areas where a normal electrical supply is not available. Generally, in the rural areas, people use dry cells for their torches. A cell comprises an arrangement of chemically active materials whose reaction produces electric energy when the external electric circuit is completed. Basic parts of an electric cell are: (a)        a positive electrode (anode),     (b)    a negative electrode (cathode),      (c)        an electrolyte (active reagent). The electrolyte reacts with either one or both electrodes to produce electric energy. Reaction stops when the electric circuit is opened. There are two types of cells: 1.        Primary Cells                 ...

  SOUND WAVES AND SOUND INSTRUMENTS Sound is a form of energy produced by vibrating bodies. For example, when we strike a turning fork, its prongs vibrate. These vibrations give rise to sound waves. Transmission of sound waves Sound is produced by vibrating bodies. The vibrations cause the surrounding air to vibrate also producing a disturbance of the air. This disturbance travels out from the source of vibration in the form of longitudinal waves. We can demonstrate the production of sound in the laboratory using a turning fork. The  turning fork has two steel prongs which vibrate when struck with a hard rubber giving some sound. During the vibration the prongs of the turning fork present a hazy appearance due to their rapid to and fro movements. If the vibrating prongs are dipped into a beaker of water, the water is seen to be violently agitated. Also when a smaller rubber ball suspended by a thread is brought near the vibrating prongs, the ball is seen to be immediat...