Resistance,+Voltage+and+Current

=R=V/I=

In a circuit,when current flows and there is a load in a circuit, there is a potential difference in the circuit as energy is transferred to the load. Using the formula R=V/I, we can understand the relationship between voltage, resistance and current in a circuit

Voltage/potential difference
When a dry cell is connected to a light bulb, the electrical energy provided by the dry cell is converted into light and thermal energy by the bulb. This amount of energy converted accross the light bulb for each unit charge is called the potential difference. The SI unit for voltage is volt(V).

Resistance
Resistance is a measure of how difficult it is for an electric current to pass through a material. Hence it is a property of a material that restricts the movement of free electrons. Resistance is measured by calculating the ratio of the potential difference V across it to a current I flowing through it. The SI unit for resistance is ohm(Ω)

Resistivity
The resistance of a material is also dependent on its: (i)Length (ii)Cross-sectional area or thickness of wire (iii)type of material

Experimental results have shown that the larger the cross-sectional area of a wire, the lower its resistance. It has been found that the resistance R is inversely proportional to the cross-sectiional area A when the length and type of material are the same. Therefore, R is inversely proportional to A,


 * R=k/A**

Experimental results have also shown that the longer the wire, the greater the resistance. The resistance R is found to be directly proportional to the length L when the cross-sectional area and the type of material are the same. Therefore, R is directly proportional to L,


 * R=kA**

Combining both equations, we get


 * R=kL/A**

Materials with lower resistivities are better conductors of electricity. Therefore, copper is a much better conductor of electricity than nichrome and this is why connecting wires in electric circuits are usually made of copper.