Resistivity affects the resistance. The resistance is a property of the wire or other electrical components, whereas the resistivity is a property of the material used to make the wire or component. \(R= ρ\frac{l}{a}ohms\)As per the formula, both are directly proportional when other factors like length and area of cross-section have remained constant.

 As resistance and current are inversely proportional, as the resistance is halved, the resistance automatically becomes double.

Resistance is used to limit the current in the circuit, it opposes the flow of current to a level depending upon its value, and voltage drop, and its the basic property of all the conducting materials.

Resistive elements are used in almost all electrical and electronic circuits, and they are conductors that resist current flow, produce heat and light in filament lamps, and are used as heating elements.

Unknown resistor can be calculated using colour coding of resistors and using a multimeter. In some cases, we can perform some circuit calculations like the ohms law experiment.