# What is the mass of water that is heated from 20 to 100 degrees using a 500 W

**What is the mass of water that is heated from 20 to 100 degrees using a 500 W electric heater for 35 minutes if it is known that the efficiency of the heater is 64%.**

To find the value of the mass of water heated on the taken electric heater, we apply the formula: η = Sv * m * (t – t0) / (P * t), whence we express: m = η * P * t / (Sv * (tк – t0 )).

Variables and constants: η – efficiency of the taken electric heater (η = 64% = 0.64); P – power (P = 500 W); t is the duration of the electric heater operation (t = 35 min = 2100 s); Sv – specific heat capacity of water (Sv = 4200 J / (kg * K)); tк – final temperature (tк = 100 ºC); t0 – initial temperature (t0 = 20 ºC).

Calculation: m = η * P * t / (Sv * (tc – t0)) = 0.64 * 500 * 2100 / (4200 * (100 – 20)) = 2 kg.

Answer: On the taken electric heater, 2 kg of water was heated.