# Difference between parallel and series

1. Feb 19, 2007

### cy19861126

Difference between parallel and series circuit

Okay, I am really confused about parallel and series and their differences. I know how they are set up, but I do not know how their arrangements may change the circuit may result in a change in total resistence. From my lab, I know that connecting the light bulbs in series will make the light less bright than it is by itself and connecting in parallel won't change the brightness at all!

My questions are: (and I will put my thoughts into the questions)
1. How would the different arrangement (series and parallel) affect the total resistence of the circuit? From the result of my lab, I think that there is going to be more resistence in series than parallel

2. In a two bulb series circuit, how does the current through the battery in a single-bulb circuit compares to the current through a battery in a two-bulb series? Current through the battery in a single-bulb circuit is going to be more than a two-bulb series circuit

3. How does the amount of current through a battery connected to a single bulb compare to the current through a battery connected to a two-bulb parallel circuit? The two bulb parallel is going to have more amount of current going through the battery

4. Would the total resistance of a circuit increase as the number of parallel branches is increased or decreased? No.

5. Does the amount of current through a battery seem to depend on the number of bulbs in the circuit and how they are connected? For parallel, current through a battery increases compared to a single bulb circuit. For series, current through a battery decreases compared to a single bulb circuit

6. In the first picture below, rank the networks A-C according to their resistence? B>C=A

7. In the second picture below, rank the networks below according to resistence? C=E>B>D=A

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Last edited: Feb 19, 2007
2. Feb 19, 2007

### Mindscrape

1) Yes, you verified this experimentally.

2) Assuming the resistance values are all equal, then yes, more current will flow through the single bulb circuit than the two bulb circuit. Ohm's law shows this pretty easily.

3) You got this one right too. Circuit reduction would show that the parallel bulb resistance will equal half of the one bulb circuit.

4) Why do you say no? I am not going to say whether it is right or wrong because it doesn't seem like you put much thought into it. What is the equivalent resistance of two equal resistors in parallel, and what about four?

5) Okay, so you have this right. Is this because you verified it experimentally or know the theory?

6) I think you want to review the equivalent resistance for resistors in parallel.

7) I am not sure why you think that resistors in parallel would not have an effect on the overall resistance. Remember in your experiment how the bulbs in parallel had more current flowing through the battery than the single bulb, could that happen if the total resistance was the same?

3. Feb 19, 2007

### cy19861126

Yeah, you're right. It seems like I have a problem of telling whether increasing bulbs in a parallel circuit would increase the resistence or not. I know that in a two bulb parallel, there is going to be more current going through the battery than the single bulb circuit. So there is going to be less resistence? This does not make sense because more current does not mean less resistance...

Let's assume that in a parallel circuit, there's going to be more resistence. To reason that out, it's simply that there are more resistors (bulbs) in the circuit. I think this makes more sense. If this is the right answer, then I have another question to #1: Why is there more resistence on series than parallel

PS: I have not learned Ohm's law, so this may be difficult for me

Last edited: Feb 19, 2007
4. Feb 19, 2007

### ranger

If we take the same bulbs, having the same resistance and but them in parallel, we would find the total resistance like so:

$$\frac{1}{R_T} = \frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_2}+...+\frac{1}{R_n}$$

Putting them in series, the resistance would equal:

$$R_T = R_1+R_2+R_3+...+R_n$$

5. Feb 19, 2007

### cy19861126

Okay, so let's say we have a two bulb parallel circuit, each of them has 5? (whatever the units may be). If I plug that into the equation, it's going to be:

1/5 + 1/5 = 2.5

So putting the bulbs in parallel is going to decrease the resistence? Can anyone verify if I did the calculations right?

One more question. If this is right, then is current related to resistence? I mean from looking at the calculations above, it seems like that current is inversely related to resistence

Last edited: Feb 19, 2007
6. Feb 19, 2007

### ranger

Yup, you've got it

7. Feb 19, 2007

### ranger

Once again, you've nailed it.

8. Feb 19, 2007

### cy19861126

THANK YOU SO MUCH. I've been sitting at home for a day to think about this problem. I LOVE THIS FORUM