A transformer changes the 10,000 v power line to 120 v. if the primary coil contains 750 turns, how many turns are on the second
1 answer:
For a transformer, the ratio between the number of turns of primary and secondary coil is the same as the ratio between the voltages on the two coils:
Where
and 
are the number of turns in the primary and secondary coils, while 
and 
are the voltages on the two coils.
Using the data of the problem:
, 
and 
, we can find , the number of turns of the secondary coil:
Where
Using the data of the problem:
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Answer:
The mass of the Al-duckie should be 30 kg.
Explanation:
We will use the first law of thermodynamics:
ΔU = m·Cv·ΔT
Since the specific heat of water is 4.185 J(gºC), the change in the water's internal energy would be:
ΔU = 100 kg · 4.185 J(gºC) · (42ºC - 38ºC) = 1674 KJ
Given that no heat is lost, all the internal energy that the water loses while cooling down will transfer to the duckie. So, if the duckie has ΔU = 1674 KJ and its final temperature is the desired 38 ºC, we can calculate its mass using the first law again: