Understanding Voltage: Common Questions and Answers in Basic Physics

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Discussion Overview

The discussion revolves around the concept of voltage, particularly in relation to electrical safety and the behavior of current in different scenarios. Participants explore the implications of voltage differences in practical electricity, the functioning of live and neutral wires, and how these factors affect phenomena such as electrocution and the brightness of light bulbs.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant questions why a bird on a live wire with both feet does not get electrocuted, while one foot on the ground and the other on the wire does result in electrocution, suggesting that a potential difference is necessary for current to flow.
  • Another participant explains that if both feet are on the same wire, there is no potential difference, and thus no current flows through the bird.
  • There is a discussion about the nature of live and neutral wires, with participants noting that the live wire has a voltage reading while the neutral does not, and questioning why this is the case.
  • One participant mentions that the power in a light bulb is the product of voltage and current, and that current is determined by the resistance of the bulb according to Ohm's law.
  • Concerns are raised about whether current is still flowing in the wire and how that relates to the potential difference experienced by the bird.
  • Another participant emphasizes that voltage is a potential difference and explains the convention of measuring voltages relative to ground, which is considered to have a potential of 0.
  • A suggestion is made to use a voltmeter to measure voltage, highlighting the need to compare potentials at two points.

Areas of Agreement / Disagreement

Participants express various viewpoints on the nature of voltage and current, with some agreeing on the necessity of a potential difference for current to flow, while others raise questions that indicate a lack of consensus on the underlying principles and definitions.

Contextual Notes

The discussion includes assumptions about electrical safety and the behavior of current that may not be fully explored. There are also unresolved questions regarding the specific behavior of live and neutral wires and their voltage readings.

Who May Find This Useful

This discussion may be useful for individuals new to physics, particularly those interested in understanding basic electrical concepts and the principles of voltage and current.

Kyoma
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I think I have a wrong definition of the word 'voltage'. For example, a bird perching on a live wire with its 2 legs will not be electrocuted, but a bird perching with one of its legs on the ground and another on the wire will be electrocuted. Why? Wouldn't the current pass through the bird regardless of the bird's feets' positions? Why wouldn't it die when it has two of its feets on the wire?

Furthermore, in practical electricity, there are the live and neutral wires. The live wire records a voltage reading but the neutral doesn't. Why?

Lastly, voltage or current or both of them would affect the brightness of a light bulb?

Thanks. I'm relatively new to physics, so I need some simple answers. :P
 
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Kyoma said:
I think I have a wrong definition of the word 'voltage'. For example, a bird perching on a live wire with its 2 legs will not be electrocuted, but a bird perching with one of its legs on the ground and another on the wire will be electrocuted. Why? Wouldn't the current pass through the bird regardless of the bird's feets' positions? Why wouldn't it die when it has two of its feets on the wire?
To be electrocuted, a large number of charges in the bird's body have to move (electrical current). The charges will move only if they are pushed. In order to be pushed, a potential difference is required. If there is no potential difference between the contact points (feet) there will be no electric field (electric force) created in the bird's body to push the electrons.

If both feet are on the wire, the feet are at the same potential. There is no potential difference if both feet are on the wire (eg. +15000V to +150000V) so no current flows. If one foot is on the wire (eg. +15000V) and the other is at ground (0V), the potential difference is huge (+150000V) and current flows through bird.
Furthermore, in practical electricity, there are the live and neutral wires. The live wire records a voltage reading but the neutral doesn't. Why?
In typical household AC there are 4 wires, a red, black, white and copper (ground) wire. The copper wire is connected to ground so there is no potential difference between it and ground. The others are connected to a voltage source. There is a potential difference between those wires and from the wires to the ground.
Lastly, voltage or current or both of them would affect the brightness of a light bulb?
The power in a light bulb is the product of voltage x current. Since voltage is supplied from a constant voltage source, the current is determined by the resistance of the light bulb according to Ohm's law: V = IR; I = V/R

AM
 
Andrew Mason said:
To be electrocuted, a large number of charges in the bird's body have to move (electrical current). The charges will move only if they are pushed. In order to be pushed, a potential difference is required. If there is no potential difference between the contact points (feet) there will be no electric field (electric force) created in the bird's body to push the electrons.

If both feet are on the wire, the feet are at the same potential. There is no potential difference if both feet are on the wire (eg. +15000V to +150000V) so no current flows. If one foot is on the wire (eg. +15000V) and the other is at ground (0V), the potential difference is huge (+150000V) and current flows through bird.

But isn't the current still flowing in the wire? Aren't the electrons still being pushed in the wire?

In typical household AC there are 4 wires, a red, black, white and copper (ground) wire. The copper wire is connected to ground so there is no potential difference between it and ground. The others are connected to a voltage source. There is a potential difference between those wires and from the wires to the ground.

I know. But, why wouldn't the live wire have a zero voltage while the neutral voltage have a recorded voltage? Why does it have to be the other way?
 
Kyoma said:
But isn't the current still flowing in the wire? Aren't the electrons still being pushed in the wire?
Yes. There is very small potential difference from one end of a transmission wire to the other. That is because copper is a very good conductor. So there is almost no potential difference between the bird's two feet. A significant potential difference is needed in order to drive electrons through a bird. You will understand this better when you study electricity in greater depth.

I know. But, why wouldn't the live wire have a zero voltage while the neutral voltage have a recorded voltage? Why does it have to be the other way?
Voltage is potential DIFFERENCE. The convention is to give the earth, which is essentially electrically neutral (no net charge) a potential of 0. All other voltages are measured relative to that.

I would suggest you read a good book on electricity and see if you can answer some of these questions yourself. That is a good way to learn.

AM
 
Just to add a thought: Kyoma, have you tried using a voltmeter? In order to measure a voltage you have two leads. That's important, because as Andrew Mason discusses, you need to compare the potential at one point with the potential at another.
 

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