Some questions

Garrick_3658 SG

1. Why can birds stand on an overhead transmission cable without suffering any harm such as electrocution?

I have the answer as there is no p.d. between their feet, but why?

2. Why are overhead transmission cables found up high in the sky?

Other than the stupid answer "so no one can touch it", well, silly, I can put underground too so that no one can also touch it right. Somemore got ground insulation as well. "Double protection" heh.

My reason: Reduce heating effect of current flowing in cables so that power loss is reduced to the minimum. Temperature at a higher altitude is lower (think effect of air pressure on temperature of air molecules)

Correct? Or am I missing something?

Thanks for any help! :D

secretliker SG

Maybe digging grounds would cost more than constructing poles and hanging the wires overhead. Financial reason also.

Garrick_3658 SG

Maybe digging grounds would cost more than constructing poles and hanging the wires overhead. Financial reason also.

Then why do underground train stations exist?

skythewood SG

1. Why can birds stand on an overhead transmission cable without suffering any harm such as electrocution?

I have the answer as there is no p.d. between their feet, but why?

2. Why are overhead transmission cables found up high in the sky?

Other than the stupid answer "so no one can touch it", well, silly, I can put underground too so that no one can also touch it right. Somemore got ground insulation as well. "Double protection" heh.

Correct? Or am I missing something?

Thanks for any help! :D

no p.d.

high up so won't obstruct other stuff

Zandermccoll SG

1. When reaching the bird, the current has the 'choice' of either going through the next part of the wire without passing the bird or going to the next part of the wire while taking a 'detour' through the bird's body

My teacher uses the analogy that current 'prefers' going through the path with less resistance. Heh.

Thus, the current does not pass through the bird, because it would be a path with higher resistance than if the current just went through the wire straight.

I would post an illustration, but dunno where to host

Garrick_3658 SG

Thus, the current does not pass through the bird, because it would be a path with higher resistance than if the current just went through the wire straight.

I would post an illustration, but dunno where to host

Nonsense I would say. Try touching a transmission cable with your hands (or one hand).

skythewood SG

if you can touch it and earth yourself, you can get electrocuted.

eagle SG

Thus, the current does not pass through the bird, because it would be a path with higher resistance than if the current just went through the wire straight.

I would post an illustration, but dunno where to host

If your teacher really used the word 'choice', he/she deserves to be sacked for teaching the wrong things to students.

skythewood is right. There's no potential difference. A current only flows between 2 points if there's a potential difference between those 2 points. No potential difference means no current will flow between them.

Garrick_3658 SG

What is meant by "no potential difference"? As in the p.d. between the two points are equal? I don't get it.

skythewood SG

What is meant by "no potential difference"? As in the p.d. between the two points are equal? I don't get it.

the p.d is very very small, close to zero.

illustration is illustration, i like the choice thingie...

davidche SG

What is meant by "no potential difference"? As in the p.d. between the two points are equal? I don't get it.

yes. When you touch the cable, you are actually earthed. So there is actually pd. You wont get striked by lightning when you are in air if i am not wrong.

davidche SG

There is already reduced power loss by using those cables.

Temperature at high altitude being lower actually means more power loss(more energy loss per unit time) Think it through.

Garrick_3658 SG

the p.d is very very small, close to zero.

illustration is illustration, i like the choice thingie...

Show me how. My only question is why there is no p.d.

yes. When you touch the cable, you are actually earthed. So there is actually pd. You wont get striked by lightning when you are in air if i am not wrong.

What about planes?

There is already reduced power loss by using those cables.

Temperature at high altitude being lower actually means more power loss(more energy loss per unit time) Think it through.

If you cool the cables down, they don't get heated up as much and thus less power loss, isn't it?

davidche SG

Firstly, thermal energy is loss whether or not the temperature is high or low. Thermal energy is loss because of the heating action of the current. Since current flows, wire is heated and heat is lost.

Secondly, the environment temp being low actually means that there is more efficient heat loss.

Thirdly, efficiency has to do with per unit time. Thus power loss is more.

SBS2601D SG

Secondly, the environment temp being low actually means that there is more efficient heat loss.

Thirdly, efficiency has to do with per unit time. Thus power loss is more.

Har?

Thought cold wire = power loss because the metal atoms are closer together = more resistence? And also because the negative electrons are less able to resist the positive cations because they have less energy to overcome the bonds?

skythewood SG

Show me how. My only question is why there is no p.d.

What about planes?

If you cool the cables down, they don't get heated up as much and thus less power loss, isn't it?

___________________________________________ wire
^ ^
(finger 1) (finger 2)

p.d at finger 1 is maybe 10000, finger 2 is 1000.0001

so p.d. is very small.

the end

davidche SG

Har?

Thought cold wire = power loss because the metal atoms are closer together = more resistence? And also because the negative electrons are less able to resist the positive cations because they have less energy to overcome the bonds?

I hope you are joking because you sound totally incoherent and disoriented.

cold wire= power loss? whats the link here?

Electrons are negative. Technically, there is no negative electrons because all electrons are negative.

why need to resist cations?

whats up with overcoming the bonds?

SBS2601D SG

I hope you are joking because you sound totally incoherent and disoriented.

cold wire= power loss? whats the link here?

Electrons are negative. Technically, there is no negative electrons because all electrons are negative.

why need to resist cations?

whats up with overcoming the bonds?

Erm.

We know that resistence varies with temperature.....try arguing that. Laughing

Edit: In fact, I looked at your reasoning and went Laughing .

skythewood SG

Erm.

We know that resistence varies with temperature.....try arguing that. Very Happy

try this...

if the temperature difference is bigger, the heat lost is more.

for example, a ice cube will not melt fast in an air con room, but melt very fast in the sun.

the resistance varies with temp stuff happens. but not by much.

SBS2601D SG

try this...

if the temperature difference is bigger, the heat lost is more.

for example, a ice cube will not melt fast in an air con room, but melt very fast in the sun.

the resistance varies with temp stuff happens. but not by much.

Gotcha.

Guess I've given my physics all back.

So it is a factor....hmm.