An electric kettle has two heating coils. When one of the coils is connected to an AC source, the water in the kettle boils in 10 min. When the other coil is used, the water boils in 40 min. If both the coils are connected in parallel, the time taken by the same quantity of water to boil will be

Question

An electric kettle has two heating coils. When one of the coils is connected to an AC source, the water in the kettle boils in 10 min. When the other coil is used, the water boils in 40 min. If both the coils are connected in parallel, the time taken by the same quantity of water to boil will be (A) 25min (B) 15min (C) 8min (D) 4min

Tardigrade Admin · Accepted Answer

We know when kettle are connected in parallel then time taken

T_{t o t a l} = \frac{T _{1} T _{2}}{T _{1} + T _{2}}

if connected in series

T_{t o t a l} = T_{1} + T_{2}

Here

T_{1}

and

T_{2}

are time taken by kettle seperately boil the same amount of water
so. in parallel

T_{t o t a l} = \frac{T _{1} T _{2}}{T _{1} + T _{2}} = \frac{( 10 ) ( 40 )}{40 + 10} = 8 min

$25 min$

$15 min$

$8 min$

$4 min$

Q. An electric kettle has two heating coils. When one of the coils is connected to an AC source, the water in the kettle boils in 10 min. When the other coil is used, the water boils in 40 min. If both the coils are connected in parallel, the time taken by the same quantity of water to boil will be

25min

15min

8min

4min

$25 min$

$15 min$

$8 min$

$4 min$