How Do Circuit Changes Affect Current and Voltage?

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Discussion Overview

The discussion revolves around a homework problem involving a simple electrical circuit with a voltage source of 115 V and a resistance of 10 ohms. Participants explore the effects of changes in resistance on current and voltage, addressing various scenarios such as open and short circuits.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant attempts to calculate the load current and the effects of open and short circuits, expressing uncertainty about several answers.
  • Another participant confirms the correctness of the no current condition for an open circuit but challenges the claim that there is no voltage across it, providing a counterexample with a battery.
  • Further discussion includes the application of Ohm's law and considerations of voltage across terminals in different circuit configurations.
  • Questions arise about the interpretation of the circuit components, particularly regarding the source resistance.
  • One participant expresses gratitude for the assistance and indicates they have resolved the problem.

Areas of Agreement / Disagreement

There is no consensus on the voltage across an open circuit, with some participants asserting that voltage exists despite the absence of current, while others maintain that no current implies no voltage. The discussion remains unresolved on this point.

Contextual Notes

Participants reference Ohm's law and the behavior of ideal circuits, but there are unresolved assumptions regarding the definitions of circuit components and the implications of infinite resistance.

Who May Find This Useful

Students studying basic electrical circuits, educators looking for examples of circuit analysis, and individuals interested in the principles of voltage and current in different circuit configurations.

Lizardus
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Homework Statement



i have a simple circuit with 115 V and a resistance of 10 ohms. i have to find :

a) load current for the circuit
b)current through circuit if the resistance becomes open circuited
c)voltage across circuit if the resistance becomes open circuited
d)current through circuit if the resistance becomes short circuited
e)voltage across circuit if the resistance becomes short circuited
f)voltage across resistor


Homework Equations



ohms law: I=V/R

The Attempt at a Solution



a) I am not sure
b)since its open circuit, there would be no current
c)no voltage because there is no current
d)not sure
e)not sure
f)11.5 volts
 
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Lizardus said:

Homework Statement



i have a simple circuit with 115 V and a resistance of 10 ohms. i have to find :

a) load current for the circuit
b)current through circuit if the resistance becomes open circuited
c)voltage across circuit if the resistance becomes open circuited
d)current through circuit if the resistance becomes short circuited
e)voltage across circuit if the resistance becomes short circuited
f)voltage across resistor


Homework Equations



ohms law: I=V/R

The Attempt at a Solution



a) I am not sure
b)since its open circuit, there would be no current
c)no voltage because there is no current
d)not sure
e)not sure
f)11.5 volts

Is the circuit in the problem the voltage source and its source resistance (the 11.5 Ohms)?

Your answer for b) is correct, but c) is not. You do not need a current to have a voltage. An open circuit has infinite resistance, so no current flows even if you have a voltage across the open circuit.
 
Lizardus said:

Homework Statement



i have a simple circuit with 115 V and a resistance of 10 ohms. i have to find :

a) load current for the circuit
b)current through circuit if the resistance becomes open circuited
c)voltage across circuit if the resistance becomes open circuited
d)current through circuit if the resistance becomes short circuited
e)voltage across circuit if the resistance becomes short circuited
f)voltage across resistor

Homework Equations



ohms law: I=V/R

The Attempt at a Solution



a) I am not sure
b)since its open circuit, there would be no current
c)no voltage because there is no current
d)not sure
e)not sure
f)11.5 volts
a: have you tried using the equation you posted?
b: correct
c: no. As an easily accepted counterexample, consider a battery of 1.5V not hooked up to anything. Clearly, as it is not hooked up to anything, zero current flows through it. However, 1.5V still exists across its terminals. In a similar fashion, a 115V voltage source is connected to the "terminals" of the "resistor of infinite resistance" aka the open circuit. How much voltage is across that resistor's terminals?
d: have you tried using the equation you posted (taking the limit as R -> 0)?
e: by the definition of an ideal wire, it has the same voltage at every point on the wire that is on the same node. So V_a - V_a = ?
f: 11.5 or 115?
 
berkeman said:
Is the circuit in the problem the voltage source and its source resistance (the 11.5 Ohms)?

Your answer for b) is correct, but c) is not. You do not need a current to have a voltage. An open circuit has infinite resistance, so no current flows even if you have a voltage across the open circuit.

Heres a crude paint drawing of the circuit in question:
 

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Thank you for all your help. i figured the problem out
 

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