Current Electricity and Electrical InstrumentMedium

Question

An electric kettale heater has two coils when one coil is switches on, the water in the kettle begins to boil after 15 minutes, when the other coil is switched on the water boils in 30 minutes.

Options

A.The water will boil in 45 minutes if the coils are connected in series.
B.The water will boil in 10 minutes if the coils are connected in parallel.
C.Water boils in 22.5 minutes if coils are connected in series.
D.Water boils in 20 minutes if coils are connected in parallel.

Solution

× 15 = msᐃQ ⇒ × 30 = msᐃQ
⇒ ⇒ R2 = 2R1
For series combination Parallel combination
Reff = R1 + R2 = 3R1
R1
× t = msᐃQ
× 15
× 15 = msᐃQ
t = 10 minute
× 15
t = 45 minute

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