• Support PF! Buy your school textbooks, materials and every day products Here!

Building a water heater- using battery and wire

  • Thread starter zapped
  • Start date
  • #1
12
0

Homework Statement


Need to heat 30mL of water from 20C to 40C in 1 min(60s).
Using 6V battery and Nickel Chromium alloy Nichrome wire that has a resistivityabout 10^-6 ohms/meter. So you use the battery and the wire to build a water heater.
Batter has no internal resistance.


Homework Equations


1How much heat energy in joules needed?
2How much power do you need to do it in the time indicated?
3What resistance should your nichrome coil have in order to produce this much power in heat?
4Can you create a coil from the wire having these perperties? (length needed)
5If the internal resistance of the battery were1/3 ohms, how would it effect your calculation?
(only explain what you have to do, dont recalculate the size of your coil)


The Attempt at a Solution


1:mc(delta)=2508J
2:total joules/time(60s) =41.8W
3:R=v/I = 0.8587 ohms
4: R needed divide by the resistance of the wire, so 857142 m
5: I dont get this part but I think that a longer time will be required?

I think the length of the wire I calculated is probably wrong, but I dont know which step I did wrong, so please help, thanks =p
 

Answers and Replies

  • #2
Delphi51
Homework Helper
3,407
10
Your calcs look good to me, but this "resistivity about 10^-6 ohms/meter" is unreasonable - better check that number! Looks like gold wire rather than nichrome.
 
  • #3
220
0
What units have you used in the first step? I got smaller amount of energy needed. And my guess would also be, that the unit of resistivity is wrong. Usually it's ohm*meter, not ohm/meter.
 
  • #4
mgb_phys
Science Advisor
Homework Helper
7,774
12
Usually it's ohm*meter, not ohm/meter.
Bulk resistivity is ohm-meter, but for wire of a given CSA you can quote Ohm/meter
 
  • #5
220
0
Bulk resistivity is ohm-meter, but for wire of a given CSA you can quote Ohm/meter
Okay. Thanks for correcting.
 
  • #6
12
0
thanks everyone
I was just unsure about the length of the wire I got
but I get it now =P
 

Related Threads on Building a water heater- using battery and wire

Replies
3
Views
1K
Replies
1
Views
1K
  • Last Post
Replies
4
Views
3K
Replies
8
Views
713
Replies
1
Views
2K
Replies
44
Views
4K
Replies
2
Views
402
  • Last Post
Replies
1
Views
3K
  • Last Post
Replies
4
Views
2K
Top