To calculate the time it will take for a heating coil to heat a given amount of water, we can use the formula:

Q = mcΔT

where Q is the heat energy transferred, m is the mass of the water, c is the specific heat capacity of water, and ΔT is the change in temperature.

In this case, we have:

m = 1.4 kg

c = 4200 Jkg^(-1)K^(-1)

ΔT = (100°C – 30°C) = 70°C

First, we need to calculate the heat energy required to raise the temperature of the water from 30°C to 100°C:

Q = mcΔT

Q = (1.4 x 4200 x 70)J

Q ≈ 411,600 J

Now, we can calculate the time it will take for the heating coil to transfer this amount of heat energy. The power (P) of the heating coil is given as 70 W (watts).

The relationship between power, energy, and time is:

P = ΔE/Δt

where P is power, ΔE is change in energy, and Δt is change in time.

In this case, we know that ΔE = Q (heat energy transferred) and P = 70 W. We can rearrange the equation to solve for Δt:

Δt = ΔE/P

Δt ≈ 411,600 J / 70 W

Δt ≈ 5880 seconds

Therefore, it will take approximately 5880 seconds or 98 minutes to heat 1.4 kg of water from 30°C to 100°C using a heating coil rated at 70 W.

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