PHYSICS

 TRIBO-ELECTRIC SERIES  The series in which the substances are arranged according to their tendency to lose or gain electrons on rubbing each other. The higher the position of the substance, it has the tendency to lose electrons and to gain positive charge on rubbing. The series of common substances  follows, Air Human hair Rabbit's fur Glass Hair Silk Paper Cotton Steel Wood Amber Rubber balloon Plastic wrap Ebonite Example: When glass rod is rubbed with silk, the rod loses electrons and get positively charged whereas silk gains electrons from the rod and gets negatively charged. Please check the position of glass in relation with silk. Glass is placed above silk.

 LONGITUDINAL WAVES The waves in which the particles of a medium vibrate in the  direction of propagation of wave are called a longitudinal wave. These waves propagate in the form of compressions and rarefactions. Example: Sound waves in air. TRANSVERSE WAVES The waves in which the particles particles of a medium vibrate in the direction perpendicular to the direction of propagation of waves are called transverse waves. These waves propagate in the form of Crests and troughs  Example: water ripples

 QUESTION  Why is food cooked quickly in a pressure cooker ? Boiling:  The process in which a liquid changes into gaseous state at a constant temperature and pressure is called boiling.  Example: water boils at 100°C to change into steam. Boiling  point: The temperature at which boiling takes place at a given pressure is called boiling point.  Example: The boiling point of water is 100°C.  Boiling of  a liquid starts when the vapour pressure of the liquid heated is equal to the air pressure above the liquid surface. If we can increase the pressure above the liquid surface then boiling is  delayed and hence the boiling point is increased.  So, when steam is retained inside the cooker, boiling point of the liquid increases to 120-125°C. As the food is cooked at higher temperature in the pressure vessel, it is cooked easily and quickly.

 PRISM Prism is a transparent retracting medium bounded by at least two plane surfaces inclined at a certain angle. ANGLE OF PRISM The angle between two retracting surfaces of a prism is called angle of prism. ANGLE OF DEVIATION The angle between the direction of incident ray and the emergent ray is called angle of deviation.  The angle of deviation depends on 1. Angle of incidence.  With the increase in the angle of incidence , the angle of deviation first decreases ,then reach a minimum value then it also increases. 2.Refractive index of the material of the prism. With the increase in the refractive index angle of deviation increases. 3. Colour o wavelength  of light  With the increase in wavelength of light used, the angle of deviation decreases . Red is deviated the least and violet the most.  4. Angle of prism or thickness of the prism  The angle of deviation increases with increase in the  the angle of  de prism.

  PASCAL'S LAW : The pressure exerted at any point in a confined liquid is transmitted equally and undiminished in all direction throughout the liquid. Pressure at a point in a liquid =F/A, Pressure at any other point in the liquid=F'/A' As pressure is transmitted equally,   F/A=F'/A' Applications 1.Hydraulic press. 2. Hydraulic lift. 3.  Hydraulic brakes.

 CRITICAL ANGLE: The critical angle is the angle of incidence in the denser medium for which the angle of refraction in the rarer medium is 90°. FACTORS: The critical angle of a medium depends on 1. The relative refractive index of the denser medium with respect to the rarer medium. Greater the refractive index, smaller the critical angle.  For example: refractive index of glass is 1.5, critical angle is 42° and for diamond, refractive index is 2.4, the critical angle is 24° 2. The colour(wavelength) of the light. Longer the wavelength, greater  is the the value of the critical angle. For example:  Red has longest wavelength among seven colours, so it has maximum value of the critical angle for a medium.

 What is atmospheric pressure? Answer: The force exerted per unit area on the surface of the earth due to the weight of air  column above it is called atmoshpheric pressure. Its SI unit is N/m² or pascal. Other units are dyne/cm², mm of mercury, bar, torr,