Physics Education

Surface Tension - Liquid surface behaves like a stretched membrane. This is because liquid tries to occupy least surface area. This property of liquid is called surface tension (T). Examples Oil & water do not mix with each other. Liquid drops spherical in shape. Small insects can easily walk on the surface of water. Needle can float on the surface of water though density of steel is more than water. Cleaning of clothes by soaps & detergents; which lowers the surface tension of the water. Clinical test for jaundice. some definition from Surface Tension Molecular force - The force which keeps the molecules together is called molecular force.  Cohesive force - It is defined as the force of attraction between molecules of same substances. E.g. force of attraction bet two water molecules. Adhesive force - It is defined as the force of attraction between molecules of different substances. E.g. force of attraction between water molecules & glass molecules. Molecular...

Stress-Strain curve Region OA in the graph is linear. Hook's law is obeyed. Solid behaves like elastic body. Point A is the elastic limit . In region AB, stress & strain are not proportional. But body can  regain its original shape & size when the load is  removed.  Point B is called yield point & corresponding stress is  called yield strength .  When load is removed at point C between region B&D,  body does not regain original dimension. Even stress is zero, strain is not zero in the region BD. P oint C is called set point .  At point C the material is in a permanent set & the deformation is called Plastic deformation. Point D is called ultimate stress . At this point wire becomes thin. Point E represents break point . Where the body physically  breaks. If point D & E are very close, material is said to be brittle . If point D & E are far apart, material is said to be ductile . Ultimate stress ...

Deforming force - An applied external force which changes shape & size of  the   body; known as deforming force. The change of shape & size of the body after application of deforming force is called deformation . Restoring force - When a body is subjected to deforming force a restoring force is developed in the body. This restoring force is equal in magnitude but opposite in direction of deforming force.  Elastic body - If a body regains its original size & shape after removable of deforming force then the body is called elastic body. E.g.   spring, rubber, balloons, Jelly, tennis ball etc. Elasticity - It is defined as a property of a body through which body tends to regain its original size & shape on removal of deforming force. Plastic body - If a body does not regain its original size & shape after removable of deforming force then the body is called plastic body. E.g. wax, putty, toys made of clay etc. Plasticity - It ...

Elastic limit  - The maximum stress which can be applied on a body without permanent deformation is called elastic limit. Hook's law - Within the elastic limit stress developed in a body is directly proportional to strain produced in it. Elastic constants & their relation Corresponding to three different types of stress & strain; there are three different modulus of elasticity. (i)  Young's Modulus (Y)  (ii)  Bulk Modulus (K) (iii)  Modulus of rigidity (η)  Young's Modulus (Y) Within the elastic limits, ratio of longitudinal stress to  longitudinal strain is called as  Young's Modulus denoted by "Y". Bulk Modulus (K) Within the elastic limits, ratio of volume stress to  volume  strain is called as  Bulk Modulus denoted by "K". Negative sign indicates that when pressure   increase volume decrease and vice versa. Compressibility Reciprocal of bulk modulus of elasticity is know...

Young's double slit experiment Young's in 1801 demonstrated the phenomenon of interference of light by a simple experiment. S is a narrow slit (of width 1 about 1 mm) lighted by a monochromatic (same color and wave length) source of light of at a suitable distance (about 10 cm)  from s, there are two fine slits S 1  & S 2  about 0.5 mm, parallel to S. when a screen is placed at a distance (about 2m) from the slits S 1  & S 2 ; alternate bright & dark fringes appear on the screen. The fringes disappear when one of the slits S 1  & S 2  is covered. click here to know basic of interference Explanation - Young's experiment can be explained on the basis of interference of light. According to Huygens principle, source of light "S" sends out spherical wave fronts. Let the solid arcs represent the crest & dotted arcs represent the troughs. These wave fronts reach the S 1  & S 2  click here to know about wavefron t ...

Spherometer A spherometer is an instrument for the precise measurement of the radius of curvature of a spherical surface. It consist of a base circle of three outer legs; & a center leg, which can be raised or lowered. Pitch - It is the distance between two consecutive threads of a screw or It is the distance moved in one rotation by screw. zero Error - When the central leg touches the same surface as the other three legs are; & if zero of the circular scale does not coincide with the  zero of the  main scale then the instrument have zero error. It is of two types- (i)   Positive zero error= “0” of the circular scale lies below the "0” of the main scale. (ii)   Negative zero error= “0” of the circular scale lies above the "0” of the main scale. Total Reading(R)     Where L = the distance between the any two legs. h = height of curve surface from center leg. Formula for h = M.S.R + C.S.R x L.C C...

Huygens wave theory This theory tells us as to how new waves are formed & how they propagate. Light travel in form of longitudinal waves, with uniform velocity in homogeneous medium. Different colors are due to different wavelengths. When wave enter our eye & gives energy we have sensation of light. The waves are formed in a hypothetical medium "ether" which is present everywhere in universe Success – It could explain Interference, diffraction, Reflection & Refraction.     It predicts that in denser medium its wave length will be decreased hence velocity will decrease. Experiments proved it. (Supported it) Failure- It could not explain polarization, Compton effect, photo electric effect. And light is transverse. Existence of ether could not be proved as there are no traces of drag by Michelson Morley experiment. Energy of wave does not depend on its amplitude but depends on frequency. Color doe...

Newton's corpuscles theory 1) Every source of light emits large number of tiny particles known as corpuscles in a                medium surrounding the source.    2) The tiny particles travel with high velocity, perfectly elastic, & having negligible mass. 3) The corpuscles would travel faster in the denser medium than in rarer medium. 4). When the corpuscles hit our retina in the eye, we get a sensation called light. 5). Different colors of light are due to different size of corpuscles. Corpuscles theory could not explains 1) Reflection & refraction on the surface of liquid. 2) Could not explain about Interference, diffraction & Polarization. 3) Speed of light in denser medium as per corpuscular - theory should increase, but in              practice found to be decrease. 4) The mass of source must decrease after long emission but i...

Dispersion of light It is the phenomenon of splitting of a beam of white light into its constituent colors on passing through a prism. The band of seven colors so obtain is called the spectrum .  Cause of dispersion is each color has its own characteristics Wavelength (λ). The order of colors from lower end of the spectrum is Violet(V), Indigo(I), Blue (B), Green(G), Yellow (Y), Orange (O), & Red (R); & can be recollected by the word VIRGYOR. In the above figure violet color is deviates from maximum angle & Red color deviates from minimum angle. Dispersion is denoted by ઠ(Delta). ઠ = ( μ−1)A where μ= Refractive Index of Prism’s medium            A= Angle of Prism. Angle of Dispersion : Angle of Dispersion = ઠ V - ઠ R                                      Angle of Dispersion   = ( μ V...