Why does arranging the resistors in parallel in a circuit decreases the resistance?

Question

Why does arranging the resistors in parallel in a circuit decreases the resistance?

Answer 1

if the resistors R1 and R2 are arranged in series, R(total) = R1+R2

lets say R1 = 5 Ohms, R2 =3 Ohms, then R(total)=8 Ohms.

if the resistors are in parallel, 1/R(total) = 1/R1 +1/R2 =1/5 +1/3 = (3+5)/15

and R(total)=15/8 =1.875 Ohms

Answer 2

Another good analogy is water in pipes...

Voltage = water pressure

Current = water flow rate

Resistance = pipe narrowness

A narrow pipe limits the flow rate. Put 2 pipes in parallel and you get double the flow rate.

Similarly, if you put 2 identical resistors in parallel you get half the resistance, and double the current.

Answer 3

In a simple electrical circuit consider the threee basic components

Voltage = The supply, or source

The Current =  the flow of electrons

The resistance =  the degree of difficulty the electrons experience trying to flow through the circuit.

Now consider series and parallel circuits using a racecourse scenario

racehorses represent the electrical current 1 horse = 1 amp

fences represent the resistors 1 fence = 1 ohm

Each fence is only the width of one horse so only one horse can jump at a time.

If we put the fences in series that is one after the other the horses must line up one behind the other to jump the fences one at a time

The flow rate is 1 horse per fence or electrically 1 amp

If the fences are put in parallel that is side by side then each horse can jump a fence at the same time that is 10 horses or ten amps

Consider a train with 100 passengers the train stops and only one exit door opens passengers exit one at a time

If we open 10 doors then passengers can exit 10 at a time the doors are similar to resistors in parallel  

If we arrange the fences in series the The horse jum  

Answer 4

Simply put, the more branches you add, the more paths there are for current. The more paths for current, the less overall resistance (to current) there is in the circuit.

It is kind of like adding more lanes to a highway. A four lane highway offers less resistance to the "flow" of traffic than a two lane highway, because there are more places for it to flow.

Answer 5

Some circuit application requires a precise resistance or wattage. This resistor is not existed in the market. Therefore,the designer has no choice but to use what existed resistors in the market to fulfil the design. Because resistor is a low cost part, to order a special value or wattage resistor from a manufacture is expensive or it requires to order 10,000 or more pieces to meet the minimum order.