Where,

V is the voltage in volts (V)

I is the current in amperes (A)

R is the resistance in ohms (Ω)

Unit Of Resistance

The S.I. unit of resistance is measured as volts per ampere or ohm (Ω).

• 1 Ω = 1 Volt∕1 Ampere = 10⁹ emu of resistance
• The dimensions of resistance are thus calculated as [ML²T^-3A^-2].

How Resistance Works?

• The temperature, length, and the type of the substance through which electricity is flowing determine the resistance of a substance.
• Electricity flows more freely through metals in general due to their low electrical resistance.
• The flow of electric current in metals depends on the type of metal, and it increases in the following order: silver -> copper -> gold -> aluminium -> iron.
• Furthermore, resistance decreases with a fall in temperature, while it increases with a temperature rise.
• Furthermore, there is an increase in resistance depending on the length over which current needs to travel.
• Because electricity flows more freely across a large cross-sectional area, conductors with a large area have lower resistance, whereas conductors with a smaller area have higher resistance.

Types Of Arrangement Of Resistance 

There are two basic and easy ways to connect or arrange the cells and resistance in a circuit diagram. These are: 

• Series Combination 
• Parallel Combination 

1.  Resistance in Series Combination

• In electronics, a series resistance will indicate that the resistors are all connected in order and that the current can only pass through one passage.
• The overall circuit resistance is the sum of individual resistances.
• The current that flows through each point in the circuit is the same.
• The sum of all individual voltages in the circuit gives the total voltage.
• The total resistance (R_Total) in a series circuit can be calculated using the formula: R_Total = R₁ + R₂ +R₃ 

2. Resistance in Parallel Combination

• The total resistance (R_Total) of the circuit is calculated by adding the reciprocals of all the individual resistances.
• The voltage at each point in the circuit is the same.
• The total current drawn is the sum of individual current that flows across the circuit.
• The total resistance in a parallel circuit can be calculated using the formula: 

1/R_Total = 1/R₁ + 1/R₂ + 1/R₃ + …

Resistance Properties

There are several factors on which the resistance properties may depend on a conductor. These factors have been discussed below.

1. The length – The resistance is always directly proportional to the length of the conductor in use. This means R∝ L.

• For example, a wire with conducting properties and the resistance R is divided into n equal parts. As a result, the resistance of each component will be R∕n.

3. The cross-sectional area – The resistance is always inversely proportional to the area (cross-sectional) of the conductor in use. This means R∝ 1∕A.
4. The material – The resistance is dependent on the nature of the material of the conductor in use. This means R∝ 1∕n.

• For various conductors, the value of n will be different. 
• As a result, the value of resistance (R) will also vary.

4. The temperature – Whenever a metallic conductor gets heated, the metal’s atoms vibrate with higher amplitude and frequency about their mean positions. As a result, the number of collisions amongst all the free electrons and atoms grows.

• This phenomenon causes a reduction in the relaxation time of the conductor (τ).
• As a result, the value of resistance (R) will increase.
• This means, for a conductor, the Resistance ∝ temperature.

5. The potential difference – The resistance of a conducting body is not unique.

• It is determined by the length and cross-sectional area of the conductor.
• That is, how the potential difference is applied makes a significant difference.

The Resistance Of Various Electrical Materials 

The resistance of various electrical materials is discussed below, w.r.t. their variance with temperature.

• For metallic bodies – Metals have a temperature coefficient of resistance greater than zero. As a result, resistance will rise as the temperature climbs.
• For non-metallic solid bodies – Because of the absence of free electrons in non-metallic solids, the resistance will be independent of temperature in these bodies.
• For semi-conducting bodies – Because of the breaking of covalent bonds in semi-conducting bodies, the resistance will decrease if the temperature increases.
• In electrolytes – As the degree of ionisation increases and the viscosity of the solution decreases, the resistance will decrease if the temperature increases.
• For ionised gases – It depends on the extent to which ionisation increases; the resistance will decrease if there is an increase in temperature.
• For alloys – The resistance of alloys increases almost linearly with temperature. Alloy resistance is slightly higher than pure metal resistance.

Alloys are used to make standard resistances, resistance box wires, potentiometer wires, metre bridge wires, and so on.

• For superconductors – The resistance of certain substances (known as superconductors) becomes exactly zero at low temperatures. This temperature is referred to as the critical temperature and is determined by the nature of the substance.

Conclusion

The question relative to ‘what is resistance’ was answered by the famous physicist Georg Simon Ohm. He stated that the resistance of an electric circuit serves as an indicator that gives an estimate of how well current can flow through a circuit using the S.I. unit ohms. It is observed that there is an increase in current when the resistance decreases, and vice-versa. To make sure that current is flowing at appropriate levels in electric circuits, it is important to make use of resistors. The reader may undertake a detailed study on the myriad type of resistors and their usage to measure resistance in specific applications.