Gravitational mass by a spring balance In a spring balance, the gravitational force on a body stretches the spring and we measure the elongation of the spring. The elongation depends on gravitational force which, in turn, is proportional to the gravitational mass of the body. Thus, the elongation of the spring gives a measure of … Read more
Method for the determination of distance of star This is a spectroscopic method based on inverse square law of intensity. According to this law, the intensity of illumination at a point is inversely proportional to the square of the distance from the source of light. Here we assume that the intrinsic brightness of all the … Read more
Practical units used for measuring large masses: 1 tonne or I metric ton = 1000 kg 1 quintal = 100 kg 1 slug = 14.57 kg 1 pound = 1 lb = 0.4536 kg 1 Chandra Shekher limit = 1 CSL = 1.4 times the mass of the sun. CSL is the largest practical unit … Read more
Practical units used for measuring time: (i) Solar day: It is the time taken by the earth to complete one rotation about its own axis w.r.t. the sun. (ii) Sedrial day: It is the time taken by the earth to complete one rotation about its own axis w.r.t. a distant star. (iii) Solar year: It … Read more
Physics in relation to society The fate of a society is closely linked to physics. Whatever is discovered in physics, it immediately affects the society. For example: 1. The developments of telephone, telegraph, telex enable us to quickly exchange messages between far off places. 2. The discoveries of radio and television have made possible the … Read more
Scope of Physics The scope of physics is very wide. Every event, which occurs around us in our daily life, is governed by one or the other principle of physics. One way of getting the idea of the scope of physics is to look at its various sub-disciplines. Another way is look at the vast … Read more
What is science? It is a systematised and organised knowledge about the various natural phenomena which is obtained by careful experimentation, keen observation and accurate reasoning. The Sanskrit word Shastra and Arabic word Ilm also have a similar meaning i.e., organised knowledge. What are physical and biological sciences? Two types of sciences. The knowledge of … Read more
Failure of Classical Wave Theory According to wave theory, light is an electro-magnetic wave consisting of electric and magnetic fields with continuous distribution of energy over the region over which the wave extends. This wave picture of light could not explain the basic features of light as explained below. According to the wave theory, when … Read more
On the basis of the experimental results on photoelectric effect, Lenard and Millikan gave the following laws of photoelectric emission: For a given photosensitive material and frequency of incident radiation, (above the threshold frequency), the photoelectric current is directly proportional to the intensity of light. The saturation current is directly proportional to the intensity of … Read more
What is electron emission? The phenomenon of emission of electrons from a metal surface is called electron emission. Different methods of electron emission For the emission of electrons from the metal surface, the energy of electrons must be higher than the work function of the metal. For their release from the metal surface, the electrons … Read more
