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Scientific calculation in junior high school (electric energy) A common table lamp with adjustable brightness (the bulb is marked with the words "220 V, 25 W") adjusts the brightness of the table lamp through a knob type sliding rheostat. If the power of the table lamp changes between 16 W and 25 W in the process of adjusting the sliding rheostat, then: (1) what is the maximum resistance of the sliding rheostat? (2) how many degrees of power consumption does each table lamp normally work for 2 hours in a month (30 days)? PS：..
(1) R station = u ^ 2 / P = 220 ^ 2 / 25 = 1936 Ω
I = (P / R) ^ 1 / 2 = (16 / 1936) ^ 1 / 2 = 1 / 11 A
U = I * r = 176v
U2 = 220-176 = 44V
R = u / I = 484 Ω
(2)w=pt=25*0.001*2*30=1.5°
A calculation problem of electric power knowledge
The average height difference between the inlet section and the outlet section of a turbine is △ H = 30m, the flow velocity of the inlet section V1 = 10 / M / s, the pressure P1 = 5kgf / C ^, the flow velocity of the outlet section V2 = 4m / s, and the pressure P2 = 2kgf / C ^. Try to calculate the total head of the turbine H =? (m)
Using Bernoulli equation
H = 64.2m
Need detailed calculation process
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1. Xiaobin's height is only 165cm, but the weight is 80kg. Every day after school, he climbs the seventh floor about 20m high with a 10kg schoolbag on his back, and he is always panting. If it takes 5 minutes for Xiaobin to get to the top of the building, G is 10N / kg
2. It is known that the calorific value of gasoline is 4.6x10 ^ 7j/kg. How much heat can be released by completely burning 200g gasoline?
(2) What mass of 30 ° C water can be boiled by this heat? (regardless of heat loss)
This is very simple
1. (1) w schoolbag = g schoolbag * h building = 10kg * 10N / kg * 20m = 2000j
(2) Ptotal = wtotal / T = (80kg + 5kg) * 10N / kg * 20 divided by 300, about 56.7w
2. (1) q = MQ = 0.2kg * 4.6x10 ^ 7J / kg = 9.2x106j
(2) Q suction = cm (t-t0)
The boiling point of water is 100 ° C
M = q suction / C (t-t0) = 9.2x10 ^ 6J △ 4.2x10 ^ 3j (kg / ° C) x (100 ° c-30 ° C) ≈ 31.29
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