graph between V and I | experiment to verify ohm's law| good conductors, resistors and insulators скачать в хорошем качестве

graph between V and I | experiment to verify ohm's law| good conductors, resistors and insulators

If a graph is drawn between the potential difference readings (V) and the corresponding current values (I), the graph is found to be a straight line passing through the origin. A straight line graph can be obtained only if the two quantities are directly proportional to one another. Since the ‘current potential difference’ graph is a straight line, we conclude that current is directly proportional to the potential difference. It is clear from the graph OA that as the potential difference V increases, the current I also increases, but the ratio V I remains constant. This constant is called resistance of the conductor. If we can show that for a given conductor, say a piece of resistance wire (such as a nichrome wire), the ratio potential difference/current is constant, then Ohm’s law will get verified. Alternatively, we can draw a graph between the potential difference (V) and current (I), and if this graph is a straight line, even then Ohm’s law gets verified. Let us see how this is done in the laboratory. Suppose we have a piece of resistance wire R (which is the conductor here) (and we want to verify Ohm’s law for it, that is, we want to show that the conductor R obeys Ohm’s law. For this purpose we take a battery (B), a switch (S), a rheostat (Rh), an ammeter (A), a voltmeter (V) and some connecting wires. Using all these and the conductor R we make a circuit To start the experiment, the circuit is completed by pressing the switch S. On pressing the switch, a current starts flowing in the whole circuit including the conductor R. This current is shown by the ammeter. The rheostat Rh is initially so adjusted that a small current passes through the circuit. The ammeter reading is now noted. This reading gives us the current I flowing through the conductor R. The voltmeter reading is also noted which will give the potential difference V across the ends of the conductor. This gives us the first set of V and I readings. The current in the circuit is now increased step by step, by changing the position of the sliding contact C of the rheostat. The current values and the corresponding potential difference values are noted in all the cases. The ratio potential difference /current found that the ratio V/ I or V/ I is calculated for all the readings. It is has constant value for all the observations. Since the ratio of potential difference and current, V /I is constant, Ohm’s law gets verified because this shows that the current is directly proportional to potential difference. The constant ratio V/ I gives us the resistance R of the conductor. So, this Ohm’s law experiment can also be used to determine the resistance of a conductor. If a graph is drawn between potential difference readings and corresponding current readings, we will get a straight line graph showing that current is directly proportional to potential difference. This also verifies Ohm’s law. On the basis of their electrical resistance, all the substances can be divided into three groups : Good conductors, Resistors and Insulators. Those substances which have very low electrical resistance are called good conductors. A good conductor allows the electricity to flow through it easily. Silver metal is the best conductor of electricity. Silver metal is the best conductor of electricity. Copper and aluminium metals are also good conductors. Electric wires are made of copper or aluminium because they have very low electrical resistance. Those substances which have comparatively high electrical resistance, are called resistors. The alloys like nichrome, manganin and constantan (or eureka), all have quite high resistances, so they are called resistors. Resistors are used to make those electrical devices where high resistance is required. A resistor reduces the current in a circuit. Those substances which have infinitely high electrical resistance are called insulators. An insulator does not allow electricity to flow through it. Rubber is an excellent insulator. Electricians wear rubber handgloves while working with electricity because rubber is an insulator and protects them from electric shocks. Wood is also a good insulator.