total resistance of a parallel circuit

[Virtualcom13at]

Hi,
Question- Why is the total resistance of a parallel circuit always lower than the lowest resistor?

I feel i have read lots on parallel circuits and googled it many times but still cant figure it out.
The four answers i have to use are:

A=The current is the same across each resistor
B=the total current is less than that used by the loads
C=Has the same effect as increasing the csa of a cable
D=has the same effect as decreasing the csa of a cable

Im thinking the answer is B.
Can someone please tell me the answer but also explain a little why?
Thanks

 

[mattmoo1974]

The Resistance cant be higher then the lowest value.
In series you add them ie 5ohms+10+10+10=35ohms
In parallel you divide the resistance into 1 so 1/5=0.2 +1/10=0.1 +1/10=0.1 +1/10=0.1 << add all these together= 0.5
And then 1/0.5=0.2
0.2 is less then 0.5 as above, The total current is less than that used by the loads.
I hope this makes sense, Iv confused myself a few times

I just remebered it as Series Higher then highest value!
Para Lower then lowest value!

 

[Des 56]

Think of the resistance as just a length of cable
Apply a voltage and a current flows,the value of the current that flows will depend on how much resistance there is to that flow
Connect another length of wire in parallel with the first.you are literally doubling the size of the first cable
Because the area is now larger the resistance to the flow is less even though the applied voltage remains the same

 

[mattmoo1974]

Now you ve confused me des! Am i right? iv had a few stella's this afternoon

 

[Virtualcom13at]

Thanks for the replys. think im sort of getting it. just trying to get that answer from the study books seemed impossible. makes me feel like i need a few stellas or Bulmers. :drool5:

 

[Des 56]

A way to see the effect of area to resistance is to look in the book for resistances of copper conductors,make a graph of cable size on the one axis and resistance on the other.
Choose some cable sizes plot the values that are given,then draw a line through them

You will see the resistances decrease as the cable gets bigger

 

[Jurasic Spark]

Hi,
Question- Why is the total resistance of a parallel circuit always lower than the lowest resistor?

I feel i have read lots on parallel circuits and googled it many times but still cant figure it out.
The four answers i have to use are:

A=The current is the same across each resistor
B=the total current is less than that used by the loads
C=Has the same effect as increasing the csa of a cable
D=has the same effect as decreasing the csa of a cable

Im thinking the answer is B.
Can someone please tell me the answer but also explain a little why?
Thanks

If you connect 4 x 2.5mm cables tohether in parallel you effectively have a 10mm csa cable. The answer is C

 

[mattmoo1974]

Its a C@G question it could be all 5 answers

 

[Virtualcom13at]

This is not helping. so now im confused again.

 

[telectrix]

the answer is C. jurassic beat me to it. think of water in a pipe, say its a 22mm pipe feeding a 10mm, the flow is restricted bt the smaller pipe. now add another 10mm pipe in parallel, that will double the water flow.which is like doubling the csa of a cable.and so on.

 

[Virtualcom13at]

I will go with C.
Still need to understand it abit better tho but i have only been a student for two months whilst working full time so im happy with my progress.
Cheers