Factors affecting surface tension of a liquid (i) Effect of contamination: If water surface has dust, grease or oil, the surface tension of water reduces. A small piece of camphor put in clear water dances vigorously due to decrease of surface tension of water. (ii) Effect of solute: (a) A highly soluble substance like sodium … Read more
Detergents Oil stains and grease on dirty clothes cannot be removed by simply washing the clothes with water because water does not wet them. By adding detergent or soap to water, the greasy dirt can be easily removed. Cleansing action of detergents The cleansing action of detergents can be explained as follows: (i) Soap or … Read more
What is Uniform Motion? An object is said to be in uniform motion if it covers equal distances in equal intervals of time, however small these time intervals may be, in the same fixed direction. So, if an object in uniform motion covers 1200 m in 1 minute in a given direction, it indicates that … Read more
What is velocity? The rate of change of position of an object with time in a given direction is called its velocity. It can also be defined as the speed of an object in a given direction. It is equal to the displacement covered per unit time. Velocity = Displacement / Time As velocity has … Read more
What is speed? The rate of change of position of an object with time in any direction is called its speed. It is equal to the distance travelled by the object per unit time. Speed = Distance / Time Speed has only magnitude and no direction, so it is a scalar quantity. Also the distance … Read more
What is acceleration ? The rate of change of velocity on object with time is called its acceleration. It tells how fast the Velocity of an object changes with time. Acceleration = Change in velocity / Time taken Acceleration is a vector quantity. It has the same direction as that of the change in velocity. … Read more
Distance or path length It is the length of the actual path traversed by a body between its initial and final positions. As shown in Fig. 3.4, suppose a body moves from position A to B through C. Then Distance covered = AC + CB Important Points Regarding Distance: Distance is a scalar quantity because … Read more
Rest An object is said to be at rest if it does not change its position w.r.t. its surroundings with the passage of time e.g., a book lying on a table. Motion An object is said to be in motion if it changes its position w.r.t. its surroundings with the passage of time e.g., a … Read more
Atoms Atoms 12.2 Alpha-Particle Scattering and Rutherford’s Nuclear Model of Atom 12.3 Atomic Spectra 12.4 Bohr Model of the Hydrogen Atom 12.5 The Line Spectra of the Hydrogen Atom 12.6 De Broglie’s Explanation of Bohr’s Second Postulate of Quantisation Topicwise Analysis of Last 10 Years’ CBSE Board Questions (2016-2007) M Maximum weightage is of Bohr … Read more
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
