Circuits

Electricity Circuits: Individual, Series, Parallel and Compound circuit

In last week’s lab we studied basics of electricity circuit:

1. Individual CCT
 Series
 Parallel

2. Compound CCT - A cct which is made up of series and parallel ccts.

3. Ohm’s law. This law describes the relationship between Resistor, Amperage and Voltage i.e. V= AR. V = AR means Voltage (V) is equal to Amperage(A) times Resistance(Ohm). Voltage is the force that pushed current through the cct. Resistance is the force that stops the current flow through the cct. Amperage is a measurement of how much current is flowing through the cct.

4. Power law – Watt = AV. Power is produced when voltage is pushing current through resistance. Power is the product of A times V.

5. How V,A and R behave in parallel and series cct.

In the following paragraphs, I will do a demonstration of what we have done so far in our lab in the following order:

1. Series cct with one, two and three resistors.
2. Parallel cct with one, two and three resistors
3. Compound cct

We performed all this tests on a cct board as shown below

Series cct

We did the following test with series cct

•  With a light bulb of least resistance 
•       With a light bulb of more resistance 
•  Connect these two light bulbs in series 
•  Connect a third light bulb to the cct in 3. 

So now, let us look at what we did

Cct with one light bulb of least resistance

Left is the cct diagram we draw and on the right is what we did on the board. Conventional current will go from the red wire from positive to the positive connector rail, then passed to the fuse and then switch and finally to the positive lead on the light bulb. After it passes through the light bulb, it will go into the black wire from negative connector of light bulb to the negative connector rail and then back to ground.

We used a light with low resistance and then replaced it with a higher resistance one. In addition, we measured the voltage drop and amperage as follow:

Results:

Supplied voltage = 13.18V
Light 1	Light 2
Voltage drop = 13.18V	Voltage drop = 13.18V
Amperage = 0.75A	Amperage = 0.36A
Resistance calculated=17.5Ohm	Resistance calculated=36.61Ohm
Power calculated=9.90W	Power calculated=4.97W

We could see that with both cct, supplied voltage is 13.18V. The voltage drop across each resistor is the same as the supplied voltage. This is because the resistance in a cct will use up all available to it. As we can see current flow through light 1 is almost twice than light 2, this is because its resistance is only about half of light 1. A = V/R if supplied voltage is constant then amount of current flowing is determined by the variation in resistance. The power produced by light 1 is also a lot greater than light 2. This is because W=AV. If voltage is kept constant then power produced is only determined by the variation in current which is determined by the resistance.

PLEASE NOTE THAT THE VOLTAGE DIFFERENCE BETWEEN THESE TWO TESTS IS NOT CAUSED BY RESISTANCE IN LIGHT BULB BUT BY INCONSTANT POWER SUPPLY. THE POWER SUPPLY SHOULD ALWAYS STAY CONSTANT. VOLTAGE DROP ACROSS THESE TWO LIGHT BULBS WILL BE THE SAME BECAUSE BOTH OF THEM WILL USE UP ALL THE AVAILABLE VOLTAGE. TOTAL AVAILABLE VOLTAGE TO THE RESISTOR IN FACT SHOULD BE LESS THAN THE SUPPLIED VOLTAGE THIS IS BECAUSE WIRING IN THE CCT ALSO HAS A BIT RESISTANCE WITH MINOR VOLTAGE DROPS. IN THIS WORKSHEET, WE WILL JUST IGNORE THESE MINOR VOLTAGE DROPS.

In next two experiments, we connected the following ccts.


1. Two light bulbs in series
2. Three light bulbs in series


The results for light 1 and 2 in series are listed below

The results for light 1 ,2 and 3 in series are listed below

Conclusion

 Total resistance of a series cct is the sum of all resistors in the cct.

 Identical current will follow through each resistor regard less its individual resistance in a series cct.

 Available voltage from power supply is used up as voltage drop by each individual resistor according to its resistance.

 The total resistance is increased as more resistors is added into the series cct.

 The total power produced in a series cct is decreased as total resistance increases.

Parallel cct

We did the following test with p cct

Compound cct and results

Conclusion

 Total resistance of a parallel cct is the much less than the total resistance of resistors when connected in series. Total resistance of a parallel cct is calculated by 1/Rtotal = 1/R1 + 1/R2 +…+1/Rn. The more resistors is connected parallel in a cct the less total resistance will the cct has.


 Total current of the cct will split up through paralleled resistors. More current will follow through less resistance resistor.


 Available voltage all parallel connected resistors is identical.


 The total power produced in a parallel cct is increased as more parallel resistor is added, because additional resistors in parallel will provide additional current flow in a cct..










Compound CCT


Compound cct is a combination of series and parallel cct. It contains characteristics of both cct.