Shock Value B/Circuit Lab C

[Toms_42]

The correct answer would be that the current would go up and the speaker would be louder because when a circuit is wired in parallel, the total resistance must be less than any of the resistors, and since V=IR, the current would go up

yup.
I was asking because I wasnt sure if he meant the 4 resistors were in parallel with the speaker (in which case it would stay the same) or if they were replacing the old one.

also why is that a tiebreaker?

(the best tiereaker ive seen was on the kenston meteo test: How many roofs does a METAR station have? correct answer was 2, we said 4, the JV team said 18 )

[iwonder]

Actually the speaker would get louder weather they were replacing the old resistors or in parallel with the speaker, because if the just replaced the old resistor the equivalent resistance would still be lower(1/4 the original).

[Toms_42]

Actually the speaker would get louder weather they were replacing the old resistors or in parallel with the speaker, because if the just replaced the old resistor the equivalent resistance would still be lower(1/4 the original).

I meant they kept the old resistor AND added the new ones in parallel with the speaker, sorry for the confusion

[fantasyfan]

if that is true then the speaker would get quieter

[Toms_42]

if that is true then the speaker would get quieter

Actually, lets do the calculations.

For this example, lets drop the first resistor in series with the speaker to simplify things, as I am only explaining that current remains the same when another resistor is added in parallel.

Lets go with these values:

Battery: 10v
Speaker:10 ohms
Equivalent Resistor in parallel with speaker: 10 ohms

Let's find the total resistance of the circuit:

1/r=1/10+1/10
1/r=2/10
R=5ohms

Now for the current through the speaker: (voltage is 10 volts for the resistor and the speaker, and the resistance for the speaker remains at 10 ohms:
i=v/r
I=10/10
I=1 ampere

Now lets view the alternative, no resistor.

Total resistance is 10, As it is just that Of the speaker.

Current, once again:

i=v/r
I=10v/10 ohms
I=1 ampere (again)

Both currents are 1 ampere, so the speaker plays just as loud both times.

Even though some current is bypassed around the speaker in the first circuit, this is made up for by the all around lower resistance, 5 ohms instead of 10, so the total current of the first circuit doubles, but is halved again by the resistor bypassing the speaker.

[fantasyfan]

You are correct, thank you

[JSGandora]

How did people do on the nationals test? I felt the test portion was rather easy while the lab portion was pretty difficult. My partner and I placed 11th, with only one problem unable to do due to time constraints but then we messed up the lab portion. What was the answer to the name of the equivalence circuit that also said to make sure the accent in the name was in the right place? I believe that was station 2. Also, what were we supposed to answer for writing the equation for the Wheatstone bridge? Did they just want the ratio of each pair of resistors? Or was it something else?

[iwonder]

Probably the equivalence circuit was thévenin... But I'm just guess because the only other one I know is norton and it doesn't have an accent. Anyone care to describe the test in more detail? I'm really curious

[JSGandora]

I wasn't sure if it was Thevenin or not because it wasn't even a complete circuit and it had a bunch of resistors. It just occurred to me it might have been a circuit that took out the load resistor as in the process to find the Thevenin circuit. The question to draw the equivalent circuit made sense that way...darn...I'm stupid.... ><

[plaid suit guy2]

The equivalence could have been either Norton or Thevenin because they are directly related. You just had to justify your thinking.
Thevenin would be the easiest and most direct: you were given a fixed voltage source in series with a resistive network, and your best bet was to make the Thevenin equivalent: a fixed voltage source in series with a resistor.

as for the Wheatstone bridge, the equation is on Wikipedia (and, more importantly, not in my notes)

equation:


or
In a balanced bridge, Vg ALWAYS equals 0, as per the definition of a balanced bridge. it is used to measure extremely accurate resistances when three other somewhat accurate resistances are known.