Why are there only two types of electric charges?

There are two types of charges because we can establish charges only by loss or gain of electrons present in the orbits of an atom.

By losing electrons a body gets positively charged and by gaining electrons it gets negatively charged.

Electron is the fundamental charge. It's taken as negatively charged.

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MIRAGE. HOW IS IT FORMED ?

MIRAGE is formed by the phenomenon of total INTERNAL reflection of light. Mirage is formed in extremely high or low temperature conditions. For example: When a sand surface (desert) or road surface is heated, the air above this surface is also heated and rises up. As a consequence, the density of air in the lower level is less than that of upper level. Now , the light from any object starting from the upper layers (denser medium) travels to lower layers ( rarer medium), total internal reflection takes place i.e, the light is reflected back towards the denser medium. When these light rays reflected back, it seems that the light rays are refected from some bright reflecting surfaces on the ground. Hence the image is seen below the object.

PRESSURE COOKING

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.

UNIFORM CIRCULAR MOTION

In uniform circular motion, 1. Speed is constant. 2. Velocity is variable and acts along tangential direction at a point. 3. Centripetal Force and acceleration act along the radius towards the centre if the circular path. 4. Centrifugal force appears to act radially outwards. It is a virtual ,fictitious force, not a real force.

PHYSICS

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