A physicist went into the kitchen. He wanted to make a cup of tea so the first thing he does is opens the kettle and he thinks "I wonder how strong the current in the wire is that's being used to boil the water?" So he puts 2 5 0 g of water into the kettle and finds that it takes 1 minute 35 seconds to heat the water to 1 0 0 ° C .
Can you calculate the current in the wire?
Details and Assumptions :
Give your answer to 3 decimal places.
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
We know that heat gainer is given by
IVt
and
mc
△
t
.
Equating both the equations, we get:-
mc
△
t
2
5
0
×
4
.
2
×
(
1
0
0
−
0
)
I
=
IVt
=
I
×
2
3
0
×
9
5
=
2
3
0
×
9
5
2
5
0
×
4
.
2
×
1
0
0
=
4
.
8
0
5
A
H = m c Δ θ where Δ θ is the change in the temperature; m is the mass of water (in this case); H is the amount of heat (basically energy) and c is the specific heat capacity
Also, H = V i t where V is the voltage supplied; i is the current passing through coil and t is the time taken
Equating these two expressions and solving for i we get i ≈ 4 . 8 0 5
Q = P t m c Δ θ = I V t 2 5 0 ( 4 . 2 ) ( 1 0 0 − 0 ) = I ( 2 3 0 ) ( 1 × 6 0 + 3 5 ) I = 2 3 0 ( 9 5 ) 2 5 0 ( 4 . 2 ) ( 1 0 0 ) ≈ 4 . 8 0 5 A
Problem Loading...
Note Loading...
Set Loading...
P = t E = 9 5 C × 1 0 0 × 2 5 0 = V I Substituting in C = 4 . 2 , V = 2 3 0 , we can readily determine I to be 4.805 Amperes.