parallel

ONACD - Editable curriculum designed for teachers by teachers

Parallel Circuits

Branched Paths

ONACD –Editable Curriculum designed for teachers by teachers

http://www.allaboutcircuits.com/vol_1/chpt_5/3.html


ParallelFor electrical circuits the term “parallel” indicates that

components are connected in a way such that current is divided to flow through multiple components at the same time.

Household plumbing is like this. That way you can take a shower while someone else does the dishes.

Arrows indicate flow direction of positive charge. Note: negative charge flow is in opposite direction. If voltage is supplied at a constant value, as it typically is, the

following observations for current and total resistance can be made:


CurrentThe value of current can be different in different branches

of a parallel circuit.Since there are multiple paths for the current to flow, a

break in one path does not prevent the other paths from working.

Household circuits are like this. Each device can be turned on or off without affecting other devices.


Total ResistanceThe addition of more resistors in parallel reduces the total

resistance.Parallel resistors provide multiple ways for the current to flow.

Thus the total current increases as the total resistance decreases.

Notice that since all the components in a parallel branch has

the same start point and end point: the voltage across all the resistors is the same.

Suppose you had 5 hoses and needed to drain a pool. If you connect the hoses together in series the water would only flow slower. Run the hoses in parallel you drain the pool 5 times faster!


Total ResistanceIn a parallel circuit total resistance is calculated by

adding the reciprocal of the resistors together: Where RT is resistance total and R1, R2, R3,… are

the resistance of each resistor. Extension:Investigate Duel Core computer processors and

explain why this makes a computer some much faster.


Sample CalculationsConsider the following parallel circuit with two identical resistors.1.What is the:a)total voltage? 12V

b)total resistance?

12V R1=2 R2=2

A B

C

1 2 3

1 1 1 1 ...TR R R R

1 1 12 2TR

1 22TR

1TR


c) total current?

2. What is the current at A?

12A (same as total current)

at B? Only need current through R2.

V IR

12 (1)I

12I A

V IR

2 2 2V I R

212 (2)I

2122

I

2 6I A


c. at C?12A (same as total current)

3. What is the Voltage across:a. A to C?

Notice voltage across resistors is the same as the battery: 12V

b. A to B?There is no resistance across these points so there is no voltage drop:

0V

c. B to C?You can do a calculation with V=IR or V=(6)(2) for each resistor but

notice that there is no difference between AC and BC (this is just the voltage across the battery : 12V

Art & Photos

parallel