Phase difference of sinusoidal alternating current In a pure inductive sinusoidal alternating current, the phase of the current lags 90 degrees behind that of the voltage. If u = usin ω T, then I = isin (ω T + 90), why? Do not use advanced knowledge, please use elementary mathematical knowledge to explain The above I = isin (ω T + 90) is wrong, it should be I = isin (ω T-90)

Phase difference of sinusoidal alternating current In a pure inductive sinusoidal alternating current, the phase of the current lags 90 degrees behind that of the voltage. If u = usin ω T, then I = isin (ω T + 90), why? Do not use advanced knowledge, please use elementary mathematical knowledge to explain The above I = isin (ω T + 90) is wrong, it should be I = isin (ω T-90)

For inductive discharge: I = Du / dt; by substituting u = usinwt into the above formula, I = uwcoswt = uwsin (wt-90) can be obtained, so the phase of current lags 90 degrees behind that of voltage

The so-called three-phase alternating current is three sinusoidal alternating current with the same, maximum electromotive force and phase difference

The so-called three-phase alternating current is three sinusoidal alternating current with the same frequency, maximum electromotive force and phase difference of 120 degrees

What's the difference between negative feedback amplifier and sine wave oscillator

Negative feedback amplifier is a kind of amplifier which can stabilize the working point. It can restrain the deviation of working point caused by the rise of temperature by negative feedback, which can improve the working stability of the amplifier and broaden the frequency response range of the amplifier
Sine wave oscillation circuit works in the way of positive feedback, and produces self-excited oscillation through positive feedback. But the parameters of its positive feedback circuit are determined by calculation and design, so its oscillation frequency is within the allowable range of control, and its output frequency is also the frequency required by the designer, It must be considered and eliminated in the circuit design. The main reason is the distributed parameters of the circuit
The two circuits are not comparable except for the opposite feedback mode

() the bisection of 7a, the third power of B = - the third power of 7a, the third power of B + the third power of 2A + 1

（）=-7a²b³(-7a³b³+2a³+1)
=49a^5b^6-14a^5b³-7a²b³

1. Guess idioms by watching the clock. 2. Guess idioms
1: 12:08. 2:7:39
The most abnormal weather:
Maximum capacity:
The most dangerous moment:

I twisted my watch for two times. It's 12:08, needless to say, it's 7:39. I guess it's out of proportion or irregular. The most abnormal weather is the frost in June. The largest capacity is the universe. The most dangerous time is the collapse of the sky and the earth

Normally, the current of the small light bulb of the flashlight is 0.3A, and the power of the small light bulb is closest to ()
A. 1WB. 10WC. 100WD. 1000W

If the voltage of dry cell is 3V and the current is 0.3A, then p = 3V × 0.3A = 0.9W, that is, the power is close to 1W

If 2x ^ 3 + x ^ 2 + 13X + K decomposes a factor into (2x + 5), find the value of K and decompose the polynomial into a factor

If the original polynomial is regarded as the equation 2x ^ 3 + x ^ 2 + 13X + k = 0, then the equation has a factor of 2x + 5 = 0, that is, one root is x = - 5 / 2. When the result is substituted into the equation, it is easy to calculate K = 115 / 2, and then it is substituted into the original polynomial. By using the polynomial division method, the factorization factor is 2x ^ 3 + x ^ 2 + 13X + 115 / 2 = (2x + 5) (x ^ 2-2x + 23 / 2)

New century primary school builds a rectangular swimming pool, 50 meters long and 30 meters wide
The plan drawn is the smallest,

There seems to be a problem with the title. Is it a multiple-choice question? Does it not give the scope of the drawing

Interesting experimental composition 400 words
Don't say that about me
I'm really in a hurry
I have a request
Section 1: what experiments have been done
Section 2: clear process (with sequence)
Section 3: feeling
OK, bonus points

"I'm so happy today. I finished my homework in half an hour. It's great!
”I said to myself. What do you do with the rest of the time?
I should go to see the little goldfish my mother bought. I quickly walked to the flat round fish tank. The fish seemed to welcome me and swam up and down to me. Among them, the lion head goldfish raised its big head and swung its red and white tail, as if to show off its beauty. I suddenly wondered: why does the fish control its balance in the water?
I observed that when the fish swam, they kept swaying. Were the fins and tails working? In order to verify my conjecture, I made a bold experiment. I first prepared small scissors, fish net and gauze. Then I fished out a small grass carp feeding tortoise with the fish net. The fish seemed to be aware of the danger - struggling desperately. I silently said to the little fish, "don't be afraid, little fish, For the success of the experiment, you give it once!
”I glued the double-sided glue to my thumb and index finger and stuck the little fish. I carefully picked up the scissors and cut off the fin of the little fish. After cutting, I gently put the bald fish into the fish tank. At first, the little fish struggled for a while and then sank to the bottom of the water. After a while, it didn't swim any more. It seems that my guess is correct
I was still a little worried, so I went to the encyclopedia, which really said: the fin of a fish is for the fish to master the balance. The tail of a fish is for the direction. Through this experiment, I think it's interesting to gain knowledge through observation and experiment!
I like insects. When I have time, I go outside to observe insects. Today, I have done all my homework. Just when I want to observe insects outside, the dark night begins to fall, and the sky begins to "shed tears"!
Looking at the sky, I couldn't help sighing and thought: the weather was fine just now. It didn't rain in the morning and it didn't rain in the evening. As soon as I was going out, it began to rain. When I was worried, my mother asked me to drink wolfberry tea. When I saw it, Ma Shang was interested in it. Because I saw a lot of wolfberry floating on the top of the teacup and a few wolfberry at the bottom of the teacup, I think it's very strange. Why do some Chinese wolfberry float on the water, and some Chinese wolfberry sink to the bottom of the tea cup? I think carefully: maybe Chinese wolfberry is like a ball, with air in it, it can float on the water
First of all, I took out two medlar from the water, put one of them in the water, and flattened it with a pair of chopsticks. As I expected, medlar came out of small bubbles in the water. Then I took off the chopsticks and observed whether the medlar would sink, I saw the medlar sink slowly. Then I pushed another medlar to the bottom of the tea cup with chopsticks and took off the chopsticks. The medlar floated up slowly and finally came to the surface of the water. Alas, I finally got the idea. My guess was right, because the air in the first medlar came out, So it sank. And the second medlar had air in it, so it floated up
Through this small experiment, I learned a truth: Lycium barbarum is like a ball. If there is air in it, it can float on the water. If there is no air, it will sink
I really want to know if putting more water or less water can make mung bean sprout quickly. A few days ago, I did an experiment to test it. I took two plastic boxes, then paper towel and water, and two mung bean seeds. I put paper towel in two boxes, then 50 drops in one box and 80 drops in the other, Then I put two mung bean seeds in two boxes, and wrote the number. The one with more water is No. 1, and the one with less water is No. 2. Finally, I put the box on the balcony facing south. If I do all this well, I will know the result immediately, I stood quietly on the balcony waiting patiently for this moment. I waited for about 2 hours, and I found that the seeds in box 1 were much bigger, but the seeds in box 2 had almost no change. I waited for another 3 hours, and I found that the seed skin in box 1 was broken, But the seeds in box 2 only increased a lot. I was secretly happy and continued to wait for the moment when the seeds sprouted. About three hours later, I looked again and found that No. 1 had a foot sticking out, while No. 2 had only broken its skin. I thought: it will be a while before I know the result! After waiting for two hours, I saw that the seeds in the box with more water germinated, I let the seeds germinate faster, I cried happily: "I guessed right, I succeeded!" ah! This Mung Bean Germination Experiment benefited me a lot! Author Wang Xinning

There are three continuous even numbers whose sum of squares is known to be 56

Let the three consecutive even numbers be n-2, N, N + 2
(n-2)²+n²+(n+2)²=56
The solution is n = 4 or - 4
The three consecutive even numbers are - 6, - 4, - 2 or 2,4,6