Series circuit what went wrong?

[Eddy Current]

Use the general voltage divider formula to to complete the values of voltage drop for the following series connected resistors. Assume a source voltage of 120V.

R(1)1K
R(2)2.2
R(3)1.8
R(4)1.5


I got the totals of

Rt 10005.
It.119
Et120


I assumed .119 is a constant through out the circuit but i am not getting the right voltages for E 1-4

 

[n1ist]

As worded, I agree with you. The total resistance is
Rt = (1000 + 2.2 + 1.8 + 1.5) = 1005.5 ohms
V = 120V (given)
I = 120/1005.5 = 119mA
V1 = 0.119 * 1000 = 119V
V2 = 0.119 * 2.2 = 0.262V
V3 = 0.119 * 1.8 = 0.214V
V4 = 0.119 * 1.5 = 0.179V

Of course, what they are likely asking for (if you add the missing "K" from each value)
Rt = (1000 + 2200 + 1800 + 1500) = 6500 ohms
I = 120/6500 = 18.5mA
V1 = 0.0185 * 1000 = 18.5V
V2 = 0.0185 * 2200 = 40.7V
V3 = 0.0185 * 1800 = 33.3V
V4 = 0.0185 * 1500 = 27.8V

/mike

 

[gar]

130722-0933 EDT

Eddy Current:

I believe you have the following resistance values in series:
1000
2200
1800
1500
Just add them up
6500 ohms, and by the way these are all standard values.

Recalculate the current, and then calculate the power dissipation in each resistor.

These are all 10% tolerance values. Now assume worst case +10% and separately -10%, and calculate the results. Apply the + tolerance to all at the same time, and similarly for the - tolerance.

.

 

[Sahib]

As worded, I agree with you. The total resistance is
Rt = (1000 + 2.2 + 1.8 + 1.5) = 1005.5 ohms
V = 120V (given)
I = 120/1005.5 = 119mA
V1 = 0.119 * 1000 = 119V
V2 = 0.119 * 2.2 = 0.262V
V3 = 0.119 * 1.8 = 0.214V
V4 = 0.119 * 1.5 = 0.179V

Of course, what they are likely asking for (if you add the missing "K" from each value)
Rt = (1000 + 2200 + 1800 + 1500) = 6500 ohms
I = 120/6500 = 18.5mA
V1 = 0.0185 * 1000 = 18.5V
V2 = 0.0185 * 2200 = 40.7V
V3 = 0.0185 * 1800 = 33.3V
V4 = 0.0185 * 1500 = 27.8V

/mike

It is really due to rounding off errors that the voltages across resistances do not add up to 120V more accurately in the single 'K' case.

 

[gar]

130723-1301 EDT

Eddy Current:

You have not listed the answers to the question, nor what answers you calculated.


If n1ist had provided more significant digits for the 1000 ohm, then its voltage would be 119.2326. Adding this voltage to the others gets 120.0 V.

119.3436
000.2626
000.2148
000.1790
=======
120.0000

If rounding to 3 digits to the right of the decimal point was done, then the result is
120.001

.

 

[Eddy Current]

130722-0933 EDT

Eddy Current:

I believe you have the following resistance values in series:
1000
2200
1800
1500
Just add them up
6500 ohms, and by the way these are all standard values.

Recalculate the current, and then calculate the power dissipation in each resistor.

These are all 10% tolerance values. Now assume worst case +10% and separately -10%, and calculate the results. Apply the + tolerance to all at the same time, and similarly for the - tolerance.

.

That was it thanks! I just needed to make them into a whole number.

 

[n1ist]

It sounds like the book has some issues (as this is the second problem you have posted with errors).

Normally, if you see a resistance of 2.2, it is 2.2 ohms. I would never blindly read 2.2 as 2.2k (or 2.2M) as that would normally get you in trouble. It's quite possible to have a circuit with a 4.7K pulldown and a 2.2 ohm gate resistor, and 1.1 mOhm current shunt all around one transistor.

In this case, however, I would work backwards from the answers, find out what they screwed up, and note that on the homework assignment as it makes it clear that you really do understand the problem.

/mike