voltage across resistor

• Nov 8, 2005

• #1

Y

yahaa

Member level 1

Joined

Oct 9, 2005

Messages

36

Helped

0

Reputation

0

Reaction score

0

Trophy points

1,286

Activity points

1,566

i have 2 voltage sources say 10v and 15v connnected in parallel
and a resistor is connected in in series with combination

what will be the voltage across the resistor and what r the steps involved?????
confign is
|-----------------------
| | |
| | |
10v 5v resistor
| | |
|------------------------

 

• Nov 8, 2005

• #2

I

|IAngel|

Member level 3

Joined

Jan 26, 2005

Messages

57

Helped

4

Reputation

8

Reaction score

0

Trophy points

1,286

Activity points

852

Your drawing didn't seem to come out right...

Correct me if I'm wrong, but you wouldn't put 2 sources in parallel EVER would you? Unless if course it is batteries of the same voltage to draw more current. I haven't taken basic circuits in about 3 years now, but I remember the prof. saying you NEVER put 2 voltage sources of different magnitudes together in parallel.

Sorry - I'm no help. I'm just curious as to why you would do that...

 

• Nov 8, 2005

• #3

K

Kral

Advanced Member level 4

Joined

Mar 28, 2005

Messages

1,319

Helped

280

Reputation

558

Reaction score

84

Trophy points

1,328

Location

USA

Activity points

13,401

Yahaa,
|IAngel| is right. You don't really mean that the 2 voltage sources are connected directly in parallel, do you? If you mean that the resistor (R) is connected between the 2 voltage sources, then the current will be (15-10)/R = 5/R.
Regards,
Kral

 

• Nov 8, 2005

• #4

S

s_rampage

Newbie level 4

Joined

Oct 27, 2005

Messages

6

Helped

1

Reputation

2

Reaction score

0

Trophy points

1,281

Activity points

1,338

Well your question is not clear but still iam gonna tell you a simple method.Use SUPERPOSITION theorem.First find the voltage with one source and then with the other.after that superimpose the two results and you will get the answer.

 

• Nov 9, 2005

• #5

Y

yahaa

Member level 1

Joined

Oct 9, 2005

Messages

36

Helped

0

Reputation

0

Reaction score

0

Trophy points

1,286

Activity points

1,566

hi guys

normally this configuration for batteries is not followed.............this was asked in a competitive exam thats why

and when i apply superpositin theorm for each voltage source the other voltage source is shorted i dont know how to proceed(i get the current through resistor as 0)

 

• Nov 9, 2005

• #6

M

mayu_wakui

Advanced Member level 4

Joined

Feb 18, 2004

Messages

117

Helped

9

Reputation

18

Reaction score

2

Trophy points

1,298

Activity points

967

maybe u could post the exam question here..i'm pretty sure many would like to help..

 

• Nov 9, 2005

• #7

S

suria3

Full Member level 5

Joined

Mar 5, 2004

Messages

300

Helped

17

Reputation

34

Reaction score

5

Trophy points

1,298

Activity points

3,028

The voltages sources in general won't be appear in parallel, only the voltage drop through any loads can be appear in parallel, like the voltage divider. Pls attach the actual pic of the question.

Regards,
Suria

 

• Nov 9, 2005

• #8

L

Lord Loh.

Full Member level 4

Joined

Jun 19, 2004

Messages

196

Helped

1

Reputation

2

Reaction score

0

Trophy points

1,296

Location

Texas

Activity points

1,951

When two voltage sources are connected parallel, the resultant voltage across the setup is the lesser of the two.

As in the picture, 1000v||2v the resultant is 2v.

 

• Nov 9, 2005

• #9

H

huojinsi

Full Member level 5

Joined

Jan 21, 2005

Messages

256

Helped

25

Reputation

50

Reaction score

6

Trophy points

1,298

Activity points

2,216

To yahaa
u had better upload ur application scheme,so everyone won't guess random and give u a good guide!

 

• Nov 9, 2005

• #10

Y

yahaa

Member level 1

Joined

Oct 9, 2005

Messages

36

Helped

0

Reputation

0

Reaction score

0

Trophy points

1,286

Activity points

1,566

in the diagram provided by Lord Loh.

whats the voltage across a 2k resistor connected in parallel across the 2v batterry?

 

• Nov 9, 2005

• #11

Davood Amerion

Advanced Member level 2

Joined

Mar 1, 2005

Messages

579

Helped

116

Reputation

232

Reaction score

24

Trophy points

1,298

Location

Persia

Activity points

6,345

I dont agree with Mr Lord Loh.
we dont have ideal power and we cannot able to paralel two of them.
If 2 zener voltage paralled with each other,
lower zener voltage has dominant efect. but in the case of ideal Voltage source!!!!

 

• Nov 9, 2005

• #12

L

Lord Loh.

Full Member level 4

Joined

Jun 19, 2004

Messages

196

Helped

1

Reputation

2

Reaction score

0

Trophy points

1,296

Location

Texas

Activity points

1,951

When there are just two components, parallel and series does not make any difference. And if you have just one resistor of a sufficiently high value (that passes less current than what can be delivered by the voltage source - your battery) the voltage drop across shall be what is applied across it.

ie. 2v voltage drop.

To Davood Amerion:
I have tried this with power sources in the laboratory and got the less of the two voltage levels.

 

• Nov 9, 2005

• #13

J

jonw0224

Full Member level 4

Joined

Nov 22, 2004

Messages

211

Helped

45

Reputation

90

Reaction score

14

Trophy points

1,298

Location

USA

Activity points

2,528

Lord Loh,

Your power supplies probably had some type of current limiter or some safety mechanism. Basically, the power supplies automatically limited their current (like placing a resistor between the two supplies).

If you connect power supplies in parallel with different voltages that do not have these things (they don't have much output impedance) things get hot and blow up and you pay for two new power supplies (maybe just fuses blow if you're lucky).

You cannot put two ideal voltage sources of different ratings in parallel (solidly connected) as others have stated.

 

• Nov 9, 2005

• #14

L

Lord Loh.

Full Member level 4

Joined

Jun 19, 2004

Messages

196

Helped

1

Reputation

2

Reaction score

0

Trophy points

1,296

Location

Texas

Activity points

1,951

Okay, Fine...

I simulated the circuit in SPICE and got wired results...

But as far as the answer of an objective type question in an entrance exam is concerned, I guess one ought to tick the lower of the two values.

Any way yahaa, was the exam objective type? did you have an A, B, C, D option ?

 

• Nov 9, 2005

• #15

Y

yahaa

Member level 1

Joined

Oct 9, 2005

Messages

36

Helped

0

Reputation

0

Reaction score

0

Trophy points

1,286

Activity points

1,566

hi guys

well the choices were
5v,10v ,less than 5 , b/w 5 and 10 and more than 10

 

• Nov 9, 2005

• #16

Davood Amerion

Advanced Member level 2

Joined

Mar 1, 2005

Messages

579

Helped

116

Reputation

232

Reaction score

24

Trophy points

1,298

Location

Persia

Activity points

6,345

Just for clearing of subject; imagin similar question:
when you short circuit the ideal power source,
what is the output voltage ?!!!!

 

• Nov 9, 2005

• #17

L

Lucifre

Full Member level 2

Joined

Jul 5, 2005

Messages

125

Helped

2

Reputation

4

Reaction score

0

Trophy points

1,296

Location

Detroit MI

Activity points

2,389

yeah that question without a picture is no good

 

• Nov 9, 2005

• #18

N

Nimer

Full Member level 3

Joined

Apr 26, 2005

Messages

178

Helped

26

Reputation

52

Reaction score

8

Trophy points

1,298

Location

PALISTINE

Activity points

2,907

hi
regarding all the above , if i have to choose an answer i will choose the below 5v answer since the two power supplies will eithe shutdown or blow up , making the resistor voltage 0

regards

 

• Nov 10, 2005

• #19

L

Lord Loh.

Full Member level 4

Joined

Jun 19, 2004

Messages

196

Helped

1

Reputation

2

Reaction score

0

Trophy points

1,296

Location

Texas

Activity points

1,951

SPICE simulations make be believe that the answer shall be between 5v and 10v...

However my teacher told me that the lower of the two EMFs persists. I guess I shall have to refine my thoughts on the matter.

If we short an ideal power source, the voltage is zero the current is infinite and power output P=I*V is zero.

 

• Nov 10, 2005

• #20

Davood Amerion

Advanced Member level 2

Joined

Mar 1, 2005

Messages

579

Helped

116

Reputation

232

Reaction score

24

Trophy points

1,298

Location

Persia

Activity points

6,345

Dear Lord Loh.
By definition ideal (DC) voltage source is fixed and cannot to be zeroed!
How you can explain it?