How to judge whether RC circuit can produce oscillation? The book says to see if it satisfies the condition of φ a + φ f = 2n π. But I can't understand it

Phase shift needs to achieve positive feedback. That is to say, if the capacitor changes the phase of the sinusoidal signal, if the positive feedback is achieved, the waveform will be repeated and superimposed. Just like the water wave, if the time when the wave is excited is the peak value of the wave, the wave will be higher and higher, which is the positive feedback and the continuous enhancement of a single signal in the circuit

What does hook three strands four strings five refer to

At the beginning of Zhoubi Suanjing, one of the earliest mathematical works in China, records a dialogue in which the Duke of Zhou asked Shanggao for mathematical knowledge. The Duke of Zhou asked: "I heard that you are very proficient in mathematics. I would like to ask: there is no ladder to go up in the sky, and the ground can't be measured by ruler, so how can we get the pass

If a voltmeter with a range of 3V is connected in series with an 8K ohm resistor, the range becomes 15V. What is the internal resistance of the voltmeter? Use it to measure a certain section of electricity
When measuring the voltage at both ends, it is found that the pointer just points to 2V on the dial of the original voltmeter. What is the measured voltage?

When the series resistor is connected, it is equivalent to expanding the range of the voltmeter. The voltmeter can be divided into two parts: the meter head (the original voltmeter) and the series resistor 8000 Ω. When the meter head shows 3V, the partial voltage of the series resistor is 12V, and the current can be calculated as I = u / R12 / 8000 = 0.0015a, which is the full bias current of the voltmeter. The internal resistance of the original voltmeter can be calculated as R = u / I = 3 / 0.0015 = 2000 Ω, At this time, the partial voltage of the meter head is 2V, the current passing through the voltmeter can be calculated as I = u / r = 2 / 2000 = 0.001a, and the internal resistance of the voltmeter after expanding the range is 2000 + 8000 = 10000 Ω. At this time, the measured voltage is equal to the sum of the partial voltage of the meter head and the partial voltage of the series resistance, that is, u = IR = 0.001 * 10000 = 10V

When k is what value, the solution of the equation 3 + 8x = 7K + 6x about X is 6 times larger than that of the equation K (2 + x) = x (K + 2) about X?

The solution of equation 3 + 8x = 7K + 6x
It is X1 = (7k-3) / 2
The solution of the equation K (2 + x) = x (K + 2)
Is x2 = K
According to the meaning of the title, there are x1-x2 = 6
(7k-3)/2-k=6
The solution is k = 3

At present, the resistance wire with uniform thickness and total resistance of 40 ohm will be used. If a square metal frame is formed and its two non adjacent vertices are separately connected to the circuit with power supply voltage of 4.5V by wires, the current in the circuit will be several a

Make a square metal frame, each side length is equal, that is, divide 40 ohm resistance into 4 parts, each 10 ohm. Connect its two non adjacent vertices into the circuit with power supply voltage of 4.5V, that is, in parallel, two side length resistors (20 Ohm) and the other two side length resistors (20 Ohm) in parallel, 1 / R total = 1 / R1 + 1 / R21 / R

Let f (x) be continuous on [0, a], be differentiable in (0, a), and f (a) = 0. It is proved that there is a point where x belongs to (0, a), such that f (x) + X * f '(x) = 0

Constructing auxiliary function f (x) = XF (x)
F(0)=a F(a)=0
According to Rolle's theorem, there is a point x on (0, a) such that f '(x) = 0
That is, f (x) + XF '(x) = 0

Calculate the maximum voltage, maximum current and maximum electric power in series and parallel circuits!
There are two bulbs, which are marked with "6V, 6W" and "6V, 3W" respectively. Ask the maximum voltage, maximum current and maximum electric power that can be added in series or parallel circuit? Require calculation, reasoning in detail and high score!

The two lamps are R1, r2r1 = u, 1 ^ 2 / P, 1 = 6V * 6V / 6W = 6eu, R2 = u, 2 ^ 2 / P, 2 = 6V * 6V / 3W = 12eu (the rated below is expressed by physical quantity + 0). If the voltage of R2 in series is more than that of R1 (to ensure the safety of the two lamps), the maximum current / voltage in series is R2 normal lighting, I0 = P0 / U0 = 3W / 6V = 2 = 0.5A

Simple calculation (+ 3 5 / 6) + (- 5 1 / 7) + (- 2 1 / 6) + (- 39)
Positive 3 has 5 out of 6 plus negative 5, 1 out of 7 plus negative 2, 1 out of 6 plus negative 32, 6 out of 7

Is there a decimal point in the middle of 3 5

60V electric car with 72V charger charging car will be broken?

The actual output voltage of 72V charger is about 85, so it can't charge 60V electric vehicle

How to calculate "9.999 times 222.2 + 3.333 times 333.4"

9.999×222.2＋3.333×333.4
＝3.333×3×222.2＋3.333×333.4
＝3.333×666.6＋3.333×333.4
＝3.333×（666.6＋333.4）
＝3.333×1000
＝3333

How to judge whether RC circuit can produce oscillation? The book says to see if it satisfies the condition of φ a + φ f = 2n π. But I can't understand it