model rocket ignitor

To make a model rocket ignitor which works with AC current I connected
a piece of nichrome wire ~4cms (the heating element u'll find in old
electric stoves) . When I switced on fuse blown out in my home. The
total length of wire is 50cms and was rated 1500W. So as if the length
was reduced to nearly 10times
1.does it increased the current cosumption, or as the length was
reduced
2.due to decrease in the resistance it made a short circuit?

 

[John Fields]

On Wed, 28 Nov 2007 10:59:35 -0800 (PST), sriramveeru@gmail.com
wrote:

To make a model rocket ignitor which works with AC current I connected
a piece of nichrome wire ~4cms (the heating element u'll find in old
electric stoves) . When I switced on fuse blown out in my home. The
total length of wire is 50cms and was rated 1500W. So as if the length
was reduced to nearly 10times
1.does it increased the current cosumption,

---
Yes.
---

or as the length was
reduced
2.due to decrease in the resistance it made a short circuit?

---
Very nearly. Here:

If the original length was 50cm and it was rated at 1500 watts, then
since you have 240VRMS service in India, the resistance of that 50cm
length was:


E˛ 240˛V
R = --- = ------- = 38.4 ohms
P 1500W

and the current it would be carrying would be:

E 240V
I = --- = ------- = 6.25 amperes
R 38.4R


Then, if a 50cm piece of that wire had a resistance of 38.4 ohms, it
has a resistance of:


38.4R 0.768R
------- = --------
50cm cm

and a 4 cm length of it would have a resistance of 3.072 ohms.


Connecting that to 240V mains would try to force:


E 240V
I = --- = -------- ~ 72 amperes
R 3.072R


through a fuse probably rated for no more than 15A.


--
JF

 

[z]

On Nov 28, 1:59 pm, sriramve...@gmail.com wrote:

To make a model rocket ignitor which works with AC current I connected
a piece of nichrome wire ~4cms (the heating element u'll find in old
electric stoves) . When I switced on fuse blown out in my home. The
total length of wire is 50cms and was rated 1500W. So as if the length
was reduced to nearly 10times
1.does it increased the current cosumption, or as the length was
reduced
2.due to decrease in the resistance it made a short circuit?

pretty much.
resistance is proportional to length.
current is inversely proportional to resistance
therefore, cutting the length to 4/50 gives you 12.5 times the
current.