Voltage drop difference in closed and open circuits

  • Thread starter iser777
  • Start date
  • #1
3
0
So the voltage drops across closed circuits I get that is P = V^2/R to get the power and then you will use P=I^2/R to get the current running through the circuit and in the case the current flowing through the closed circuit is equal in every resistor and so is the voltage drop. The part that I don't get is how come the voltage drop in an open circuit would change in every resistor? and is the current changing in every resistor as well?

Homework Statement





Homework Equations





The Attempt at a Solution

 

Attachments

Answers and Replies

  • #2
PeterO
Homework Helper
2,425
47
So the voltage drops across closed circuits I get that is P = V^2/R to get the power and then you will use P=I^2/R to get the current running through the circuit and in the case the current flowing through the closed circuit is equal in every resistor and so is the voltage drop. The part that I don't get is how come the voltage drop in an open circuit would change in every resistor? and is the current changing in every resistor as well?

Homework Statement





Homework Equations





The Attempt at a Solution

In the second example, you have not so much an open circuit as a set-up with repeated reference to the Earth point. The Volt meters are not connected to measure just across a single resistor; rather from a point on one side of the resistor, all the way to Earth.
 
  • #3
3
0
So, how would I go about solving for the voltage drops? in the specific circuit?
 
  • #4
SammyS
Staff Emeritus
Science Advisor
Homework Helper
Gold Member
11,348
1,022
Which voltage drop(s) are you trying to solve for ?
 
  • #5
PeterO
Homework Helper
2,425
47
So, how would I go about solving for the voltage drops? in the specific circuit?
Has anyone ever asked you your meterage or footage, or you poundage?

I think not, they would normally ask your height and weight, and not include the units in the description.

My point is that people often refer to the Potential Difference as the Voltage - presumably because PD is measured in Volts.
At least you had the good sense to say Voltage Drop.

But what you are after is the Potential difference.

Because each Voltmeter had one terminal connected to Earth, the reading is the Electric Potential of the point the other terminal is connected to - since Earth is defined as zero Volts.

The difference between the potential to one side of a resistor, and the Potential to the other side of that resistor IS the Potential difference.
We generally accept that there is no Potential Difference across the hook-up wires, so when two resistors are connected by a wire, the Potential at each end of the wire is the same - so the Potential at the end of one resistor may be the same as the potential at the start of the next one.
 
  • #6
3
0
The one for the open circuit picture
 
  • #7
PeterO
Homework Helper
2,425
47
The one for the open circuit picture
The only difference between the two circuits is the way the Volt meters are connected.

In Circuit 1, they are connected across 1 resistor each.
In Circuit 2, they are connected across 1 only, two combined and all three combined resistors.
 

Related Threads on Voltage drop difference in closed and open circuits

  • Last Post
Replies
6
Views
2K
Replies
2
Views
10K
  • Last Post
Replies
4
Views
11K
Replies
29
Views
2K
  • Last Post
Replies
14
Views
16K
Replies
4
Views
12K
  • Last Post
Replies
3
Views
230
  • Last Post
Replies
5
Views
379
Replies
4
Views
35K
Replies
5
Views
3K
Top