There is 200ml alcohol in a glass bottle in the laboratory. The heat of alcohol in the bottle is 3 * 10 ^ 7 J / kg, and the known density of alcohol is 0.8 * 10 ^ 3kg / m ^ 3 1. How much heat can be released by burning alcohol completely 2. If only 16% of the heat is absorbed by water, how much heat is lost? 3. If all the lost heat is used, how many kg of water can be heated to 20 ℃ at normal temperature?

There is 200ml alcohol in a glass bottle in the laboratory. The heat of alcohol in the bottle is 3 * 10 ^ 7 J / kg, and the known density of alcohol is 0.8 * 10 ^ 3kg / m ^ 3 1. How much heat can be released by burning alcohol completely 2. If only 16% of the heat is absorbed by water, how much heat is lost? 3. If all the lost heat is used, how many kg of water can be heated to 20 ℃ at normal temperature?

(1) The alcohol mass is 0.8 * 0.2 = 0.16kg
Complete combustion heat release 3 * 10 ^ 7 * 0.16 = 4.8 * 10 ^ 6 joules
(2) Heat loss 4.8 * 10 ^ 6 * (1-16%) = 4.032 * 10 ^ 6 joules
(3) The specific heat capacity of water C = 4180j / (kg. ℃), q = CMT
The mass of water is m = q / CT = 4.032 * 10 ^ 6 / (20 * 4180) = 48.2kg

Solution of Joule heat in magnetic field

The solution of Joule heat generally uses two methods. In a very simple electromagnetic induction problem (for example, the induced current is constant and the time is known), q = I ^ 2 * RT can be used directly. But in most cases, the problem maker will set obstacles, and the calculation formula of Joule heat in electricity is often not feasible

Calculation of Joule heat of alternating current
Is it necessary to use the effective value to calculate Joule heat as long as it is an alternating current? If the calculation time is not an integral multiple of the period, should the effective value be used for less than one period
Explain the reason if you can

Non integer period. Less than one period should also be calculated with the effective value, there is no doubt
Because the effective value of alternating current is determined by the value of direct current, since it is the effective value, the peak and valley of waveform need not be considered
It is different from the immediate value

How many joules of electricity can 100 joules of solar energy produce

To see the conversion efficiency, generally 15%, so it is 15 joules