Is three-phase power used for lighting at home Three phase electricity is 380V. Now I want to connect it to 220V, but it's not easy to connect it. I want to connect 380V directly and use lighting electricity (220V) at home. I don't know if there's any danger. Please ask the electrician to answer, or the experienced swordsman in the Jianghu to answer,

If the power consumption is small, use a control transformer 380 to 220, it is better to use the isolation transformer 380 to 220, which is relatively safe. 500W is about more than 100 yuan

The output power of the solar cell of a certain type of street lamp is 40W. If the radiation power when the sun shines on the ground is 1000j / (s ·m2) (that is, the light energy radiated per square meter per second is 1000j), and the photoelectric conversion rate of the solar cell is 8%, how many square meters is the area of the solar panel

It is known that ptai = 40W, p'light = 1000j / (s * m ^ 2), ITA = 8%
Seek: s light
S light = WTAI / (ITA * w'light) = ptai * t / (ITA * p'light * t) = ptai / (ITA * p'light) = 40W / [8% * 1000j / (s * m ^ 2)] = 0.5m ^ 2
I think so, hope to adopt

(1) If you choose an incandescent lamp to light for 1000 hours, how much does it cost? (2) within the service life of the incandescent lamp, if the lighting time is x hours, please use the
Xiao Ming needs to buy several lamps for his home decoration. Through market investigation, the following conclusions are drawn: ordinary incandescent lamps have a power of 100 watts (0.1 kW) and a service life of 2000 hours, and the price is 3 yuan per lamp. High quality energy-saving lamps have a service life of 4000 hours, and 35 yuan per lamp. It is known that the lighting effects of these two kinds of lamps are the same, The electricity price of Xiaoming's home is 0.5 yuan per kilowatt hour (Note: electricity consumption = power (kilowatt) x time (hour), cost = lamp price + electricity charge)
(1) If you choose an incandescent lamp for 1000 hours, how much does it cost?
(2) Within the service life of incandescent lamp, if the lighting time is x hours, please use the formula containing x to express the cost Y1 of using one incandescent lamp and Y2 of using one energy-saving lamp respectively;
(3) How many hours of lighting, the cost of using these two lights is equal?
(4) Xiao Ming plans to light for 4000 hours. Please advise him which lamp is more economical by calculation?

(1) If you choose an incandescent lamp to light for 1000 hours, how much does it cost? A: Cost: incandescent lamp (100 watts) 0.1 kW * 1000 hours = 100 kwh * 0.5 = 50 yuan + lamp price 3 yuan = 53 yuan (2) within the service life of the incandescent lamp, if you set the lighting time x hours, please use the formula with X to express using an incandescent lamp respectively

A middle school plans to organize ninth grade teachers and students to hold graduation party in Shaoshan. The following is a dialogue between grade leader Mr. Li and Xiao Fang and Xiao Ming about car rental: Mr. Li: "Ping'an passenger transport company has two types of buses with 60 seats and 45 seats to rent. The rent of each 60 seat bus is 200 yuan more than that of 45 seats." Xiao Fang: "our eighth grade teachers and students were here yesterday Four passenger transport companies rent four 60 seat and two 45 seat buses to Shaoshan for a visit, with a total rent of 5000 yuan per day. "Xiaoming:" our ninth grade teachers and students rent five 60 seat and one 45 seat buses, which are just full. "According to the above dialogue, we can answer the following questions: (1) how much is the daily rent of 60 seat and 45 seat buses of Ping An passenger transport company? (2) According to the car rental scheme proposed by Xiao Ming, how much does it cost for ninth grade teachers and students to rent a car for one day?

(1) Suppose that the rent of 60 seat and 45 seat passenger cars of Ping An company is X Yuan and Y yuan respectively every day. From the solution of the equation system X − y = 2004x + 2Y = 5000, we get x = 900y = 700. Answer: the rent of 60 seat and 45 seat passenger cars of Ping An company is 900 yuan and 700 yuan respectively every day. (2) the total rent of teachers and students of grade 9 is 5 × 900 + 1 × 700 = 5200 yuan. Answer: the total fund is 5200 yuan

Observe the characteristics of the following formula and evaluate it. 1-2 + 3-4 + 5-6 + +99-100．

The original formula = (1-2) + (3-4) + (5-6) + +（99-100）=（-1）+（-1）+（-1）+… +（-1）=-1×50=-50．

What is the law of vector composition? What is the law of scalar addition?

The principle of parallelogram is used in the synthesis of vectors: two added vectors are the two adjacent sides of parallelogram, and the diagonal between them is the sum of two added vectors
Scalar addition is an arithmetic rule: 1 + 1 = 2, 1 + 2 = 3

A train runs at a speed of 20 meters per second on a flat track at a constant speed. The resistance on the train is the fourth power n of 9 × 10. Ask: 1. What is the traction force produced by the train's movement? 2. What is the work done by the traction force in one minute?

Driving at a constant speed represents the balance of forces on the train, that is, traction = resistance;
Work = force × distance, the distance of a train in one minute s = 20 × 60m = 1200m, work w = 9 × 10 to the fourth power × 1200J = 1.08 × 10 to the eighth power

LIM (cosx) (4 / X ＾ 2) (x tends to 0); process

If the largest term in the sequence {n (n + 4) (2 / 3) ^ n} is the k-th term,

These English books are not hers

These english books are not hers.