An electric heater, which is connected to a 220V circuit, can bring water to a boil in 4 minutes.

| August 3, 2021 | education

An electric heater, which is connected to a 220V circuit, can bring water to a boil in 4 minutes. During the repair, the length of the spiral was shortened from 6m to 5.5m. How long does it take now to bring the water to a boil?

The amount of heat released by the heater is:
Q = (U ^ 2) * t / R. Since the amount of heat for heating water in both cases will be the same, then:
(U ^ 2) * t1 / R1 = (U ^ 2) * t2 / R2: t1 / R1 = t2 / R2, where t1 is the water heating time before repair (t1 = 4 min = 240 s).
Electric heater resistance: R = ρ * l / S. Before repair R = ρ * l1 / S, after repair R = ρ * l2 / S.
Then: t1 * S / (ρ * l1) = t2 * S / (ρ * l2); t1 * / l1 = t2 * / l2.
t2 = t1 * l2 / l1 = 240 * 5.5 / 6 = 220 s.
Answer. It now takes 220 seconds to bring water to a boil.



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