The rated voltage is 220 V, the rated power is 840 W, the frequency is 50 Hz, the capacity is 4 L, and the bottle weighs 2 kg. Xiaoming's family has an electric kettle. The chromium brand is as the table asks. Now he puts 3 L of 20 ℃ water in the kettle, asking: (1) what's the quality of the water in the kettle? (2) How many minutes does it take to boil the water at rated voltage? (assuming that there is no heat loss under 1 standard atmospheric pressure) (3) if the actual voltage of the electric kettle is 90% of the rated voltage during the peak period of power consumption, what is the actual electric power of the kettle?

The rated voltage is 220 V, the rated power is 840 W, the frequency is 50 Hz, the capacity is 4 L, and the bottle weighs 2 kg. Xiaoming's family has an electric kettle. The chromium brand is as the table asks. Now he puts 3 L of 20 ℃ water in the kettle, asking: (1) what's the quality of the water in the kettle? (2) How many minutes does it take to boil the water at rated voltage? (assuming that there is no heat loss under 1 standard atmospheric pressure) (3) if the actual voltage of the electric kettle is 90% of the rated voltage during the peak period of power consumption, what is the actual electric power of the kettle?

(1) The mass of water: M = ρ v = 1g / cm3 × 3000cm3 = 3000g = 3kg; (2) the heat absorbed by water: q = cm △ t = 4.2 × 103J / (kg ·℃) × 3kg × 80 ℃ = 1008000j; because there is no heat loss, so w = q, the time needed to boil the water under rated voltage: T = WP = QP = 1008000j840w = 1200s = 2

The picture shows Xiao Ming's electric kettle and its name plate. He uses the electric kettle to heat 1.5kg of water from 20 ℃ to 100 ℃. How much heat does the water absorb?

Q absorption = cm (t-t0) = 4.2 × 103J / (kg ·℃) × 1.5kg × (100 ℃ - 20 ℃) = 5.04 × 105J

The name plate of an electric kettle is marked with the word "220V 1000W". When it works normally, what is the current?

What is the total luminous power of two "220 V 60 W" incandescent lamps connected in series in a home circuit?

When U2 / r = P is connected in series, the total resistance is 2R and the total power is reduced to half of the original 30W