Water is boiled at sea level in a coffeemaker equipped with an immersion-type electric heating element. The coffee maker contains 1 L of water when full. Once boiling starts, it is observed that half of the water in the coffeemaker evaporates in 18 min. Determine the power rating of the electric heating element immersed in water. Also, determine how long it will take for this heater to raise the temperature of 1 L of cold water from 18°C to the boiling temperature. The enthalpy of vaporization of water at the saturation temperature of 100ºC iss hfg = 2256.4 kJ/kg. At an average temperature of (100 + 18)/2 = 59ºC, the specific heat of water is c = 4.18 kJ/kg·ºC and the density is about 1 kg/L.

is time required to heat to boiling point form initial temperature.

Explanation:

Given:

initial temperature of water,

time taken to vapourize half a liter of water,

desity of water,

So, the givne mass of water,

enthalpy of vaporization of water,

specific heat of water,

Amount of heat required to raise the temperature of given water mass to 100°C:

Now the amount of heat required to vaporize 0.5 kg of water:

where:

mass of water vaporized due to boiling

Now the power rating of the boiler:

Now the time required to heat to boiling point form initial temperature:

energy stored in the capacitor= 9.72 x 10⁻⁴ j

explanation:

the energy stored in the capacitor is given by

e= 1/2 c v²

e= energy stored

c= capacitance= 1.5 µc= 1.5 x 10⁻⁶f

v= potential difference=36 v

so energy stored= e= 1/2 (1.5 x 10⁻⁶) (36)²

energy stored= 9.72 x 10⁻⁴j