The variation law of the terminal voltage U of a power supply with the resistance R of the external circuit is shown in figure (a), and the straight line of u = 12V in the figure is the asymptote of the line. Now, the power supply and a rheostat R0 are connected into the circuit as shown in Figure (b). It is known that the maximum allowable current of the power supply is 2a, and the maximum resistance of the rheostat R0 = 22 Ω (1) The results are as follows: (1) the electromotive force E and internal resistance R; (2) the output voltage range of a and B at no load; (3) the minimum resistance of a and B that can be connected to load

(1) When the external resistance is infinite, the terminal voltage is equal to the electromotive force. According to the figure, when the external resistance is infinite, the terminal voltage is close to 12V, so the electromotive force of the power supply is e = 12V. According to the figure, when the external resistance is r = 2 Ω, the terminal voltage is u = 6V. According to Ohm's law, the current in the circuit is I = ur = 62A = 3A

Line B is the U-I image of the resistance R. if the power supply and the resistance are used to form a closed loop, then the resistance R and the output power of the power supply are equal

According to line a, the power supply u = 3V, R0 = u / I = 3 / 6 = 0.5 Ω
According to the line B, the resistance R = u / r = 2 / 2 = 1 Ω
After the resistor is connected in series with the power supply
R total = R + R0 = 1 + 0.5 = 1.5 Ω
I = u / R total = 3 / 1.5 = 2A
P = I ^ 2 * r = 2 * 2 * 1 = 4W

The meaning of the intersection of the U-I line of the power supply and the U-I line of the resistance
The meaning of the intersection of the U-I curve of the power supply and the U-I curve of the resistance is the only working state when the resistance is connected to the power supply. This working state is the actual voltage at both ends of the resistance and the actual current flowing through the resistance. Why? If you are the one!

When the resistance and the power supply are connected into a circuit, the current flowing through the power supply and the external circuit of the power supply (i.e. resistance) must be equal, and the U-I curve of the power supply and the U-I curve of the resistance only indicate that the current flowing through the power supply and the external circuit of the power supply (i.e. resistance) is equal at the intersection point, and the intersection point of the two curves is the only working state
The principle of the above phenomenon is: the current of any section in series circuit is equal at the same time

What is the meaning of the intersection of u = E-IR and U-I in the same coordinate system?

The intersection point is the voltage at both ends and the current passing through when the resistance acts as the external resistance and the power source are connected in the same circuit;
It is also understood that the voltage and current passing through the power supply circuit are the same as the resistance
When the two resistors and the outgoing lines of the electric circle are in the same coordinate system, the output power and efficiency of the corresponding power supply can be obtained through the intersection point;
There is also a small bulb of fuante interest first rabbit and power, say electromotive force, internal resistance, let the actual power of the bulb

In the definition of ellipse, the sum of distances from F1 and F2 to the point is equal to a constant (greater than F1F2). Why is MF1 + MF2 = 2A?

According to the definition of ellipse: the distance to two fixed points on the plane and the track of a point which is equal to a constant. So as long as the distance between a point on the ellipse and its two focal points (fixed points) is equal to a constant. In order to obtain the specific value of this constant by the simplest method, we can deduce the general conclusion by assuming special cases

Ellipse: the ratio of the distance to a fixed point and the distance to a fixed line e is the trajectory of a constant point. Which fixed point is that point? Which fixed line is the directrix?

The ratio of the distance between a point on an ellipse and the two focus points and the distance between the two focus points and the guide line on the same side of the focus points is the eccentricity of the ellipse. Therefore, the ratio of the distance to a fixed point and the distance to a fixed line e is the locus of a constant point. That fixed point is the focus of the ellipse, and that fixed line is the guide line on the same side of the focus points

The elliptical orbit of the earth? The distance between the moon and the earth?
1. How many kilometers is the long axis of the earth's elliptical orbit around the sun?
How many kilometers is the minor axis?
2. Does the earth orbit the sun counterclockwise or clockwise?
3. What is the distance between the moon and the earth?
Is the orbit of the moon round or elliptical relative to the earth?
Does the moon move counterclockwise or clockwise relative to the earth?

A: the distance between the moon and the earth varies with the time of each month. There are different stages of the moon, the moon, the first chord and the last chord
Farthest point: 406000 km
Closest point: 362000 km
Average distance: 384000 km
The earth has only one natural satellite, the moon. Some people think that asteroid 3753 (1986 to) is another satellite of the earth. But in fact, although it has a very complex relationship with the orbit of the earth, it can not be called a satellite. At most, it can only be called the "partner" of the earth. Because the internal structure of the moon has solidified, its geological activities are very inactive
Some people think that the moon was formed from the same interstellar material as the earth, while some people think that it was formed by the re aggregation of fragments produced by the impact of another unidentified large body, After all, the moon is the nearest celestial body to us. It has irreplaceable significance to human beings
Mass 7.349e + 22 kg
Equatorial radius 1.2298e-02 km
The average density is 3.34 GM / cm ^ 3
The average ground distance is 384400 km
The rotation period is 27.32166 days
The cycle of revolution is 27.32166 days
The average orbital speed is 1.03 km / sec
Equatorial surface gravity 1.62 M / sec ^ 2
The equatorial escape velocity is 2.38 km / sec
Daytime mean surface temperature 107 ° C
Night mean surface temperature - 153 ° C
Maximum surface temperature 123 ° C
Minimum surface temperature - 233 ° C

A point trajectory with a constant sum of distances to two fixed points is an ellipse

That's not right. The trajectory doesn't have to be an ellipse
Two conditions are missing
(1) It needs to be in the plane
(2) The constant is greater than the distance between two points

Given that the distance between two fixed points is 5cm, and the sum of the distances from the moving point to the two fixed points is 5cm, is the trajectory of the moving point ellipse

No. It's a line segment
Attention: 5cm, 5cm! The two are equal!