Archive for June, 2011

Frictional Electricity

June 14th, 2011

Frictional Electricity:

The word electricity is derived from the Greek word ‘electron’ which means amber.  In the sixth century BC, a Greek philosopher Thales found that when a piece of amber (a kind of resin) is rubbed with fur, it acquires a remarkable property; it attracts small pieces of leaves, cork or dust. Today, we know that many other materials, such as hard rubber, nylon, plastic, glass, sealing wax etc. shows the same effect. A substance which exhibits this effect is said to be electrified or charged.

It is possible to impart an electric charge to any solid material by rubbing it with another material and amber is just one of the substances which shows the effect much strongly. It should be noted that both the rubbing and rubbed materials are electrified simultaneously. They are said to have acquired electric charges. Electrification of bodies through friction is called frictional electricity. It is also called static electricity as the charges so developed cannot flow from one point to another.

You can see this kind of effect by doing a simple experiment. Place a few tiny pieces of paper on a table. Take a plastic ruler or comb and rub it with dry hair or a piece of wool and bring it near the pieces of paper. You will observe that the pieces of paper are attracted towards the rubbed ruler or comb.

You can also see this effect when you put off your sweater in winters. Put off the sweater in a dark room and sometimes, you will observes the sparks while doing this. This is due to the same reason i.e. frictional electricity.

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Physics XI | Frame of Reference

June 6th, 2011

Frame of Reference:

Suppose someone asked you a question “How far is India?” your reaction would be “from where?” Then the person who asked you the question would tell, from here or from United States. So in kinematics some reference is very necessary to measure distances.

Suppose, you are sitting inside a stationary train. At the same time other train is moving. It is very hard to tell which of the trains is moving. If you consider yourself stationary, other train is moving while for the passenger of the other train, your train is moving.

Same is true in case of ground. For a person standing on the ground, you are moving while sitting in the train. While for the passengers sitting in the train, you are stationary.

So motion and rest are related terms depending on the position of the observer.

One Dimensional frame of Reference:

Suppose you have to locate a point (Point P as shown in figure) on a line without touching it. The solution is to mark the line and mark one point as zero (point ‘O’ in figure) and measure the distance of the point ‘P’ from the zero point. In our case the distance of P from the point is 360m.

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So we always need a ‘reference point’ from which all the distances would be measured. Same is true with the 2-Dimensional motion. In the case of 2 Dimensional motion, we need a system of coordinate axes to explain the motion.

The definition of the Reference Frame is “A system of coordinate axes which defines the position of a particle or an event in two or three dimensional space is called a Frame of Reference”.

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