How to understand for (expression 1;; expression 3)

The middle expression is used to judge whether to jump out of the loop. It doesn't mean never to jump out of the loop. Generally, there is a break method written inside the loop, otherwise the loop will be dead

What is the most commonly used theorem in high school physics

Mechanics: Newton's second law, theorem of kinetic energy, law of universal gravitation, law of conservation of mechanical energy
Electromagnetics: Faraday's law of electromagnetic induction
(electric field force ampere force Lorentz force important force)
*****Theorem of kinetic energy Newton's second law law law of gravitation
****Law of conservation of mechanical energy Faraday's law of electromagnetic induction

What can the law of "parallel with series reverse" be used in high school physics circuit?
I think many places say that the internal resistance of the power supply can not be zero and constant,
We just had a physics problem in the unified examination, which met the above conditions, but we got the wrong answer with this conclusion. I asked the teacher, he just said that this rule can only be used under certain premise, but it seems that he doesn't know any premise-
Is a certain resistance open circuit in a mixed circuit not suitable for this rule? If it is suitable, is it just as long as the resistance becomes larger? I can't do it. This is a problem for my predecessors or peers
Baidu Encyclopedia also said, "note: in general, the combination of series and reverse should also be applicable in the case of ignoring internal resistance."

"Series reverse and parallel same" means that under the condition that the internal resistance of power supply can not be ignored, the changes of current, voltage and power (or ammeter, voltage indication, brightness of light bulb, etc.) of the electrical appliances in series with variable resistance in the circuit are opposite to those of the electrical appliances in parallel with variable resistance, The variation of current, voltage and power is the same as that of resistance. This method is simple and convenient for dynamic analysis of circuit. Note: in general, series parallel reaction is also applicable when internal resistance is ignored
Generally, the internal resistance of power supply is very small, but it is not zero. It is easy to understand that there is no superconducting material in practical power supply, because all materials have resistance. In fact, the resistance should be gradually increased with the use of battery power supply, resulting in the EMF increasing in the internal resistance and the terminal voltage decreasing. For power supply such as generator, the internal resistance can be considered unchanged, It is considered that the internal resistance of the power supply does not change
The voltage and power of each resistor in series circuit are directly proportional to its resistance value. The power and current of each resistor in parallel circuit are inversely proportional to its resistance value. It is very simple to grasp these two points to analyze series parallel circuit
For example, if the resistance value of a resistor in the series circuit increases, the total resistance increases. The total current decreases, the resistance voltage U = IR decreases, and the power = I ^ 2 / R decreases. The brightness of the bulb, the reading of the voltmeter and the ammeter decrease
For another example, if the resistance value of a certain resistance in the parallel circuit increases, the total resistance increases and the total current decreases. When the internal resistance of the power supply is fixed, the resistance of the external circuit increases, which leads to the voltage increase at both ends of the parallel circuit, the current I = u / R of each branch increases, and the power also increases (P = I ^ 2 / R)
I think you are confusing the position of voltmeter and ammeter in the main or branch

Practical questions (5 11:38:16)
In the triangle ABC, ∠ B - a = 15 degrees, ∠ C - B = 60 degrees, find the degree of ∠ C

B-A = 15, so a = B-15
C-B = 60, so C = B + 60
Because a + B + C = 180, there is (B-15) + B + (B + 60) = 180
B = 45
So C = 45 + 60 = 105
The degree of angle c is 105 degrees

Two practical questions (24 21:50:8)
1. A car's fuel tank is full of oil. The first time you use half of it, you add 6 liters. The second time you use a quarter of the oil in the fuel tank, and then you add 8 liters. How many liters can the fuel tank hold?
2. The sum of the number of excavators and loaders in a development zone is 21. If each excavator excavates an average of 750m / day, and each loader transports an average of 300m / day, how many excavators and loaders are needed to transport the excavated earth immediately?

3 / 4 (x / 2 + 6) + 8 = x, x = 50, the tank can hold 50 liters of oil
2.x+y=21,750x=300y,x=6,y=15,
There are 6 excavators and 15 loaders

A square table is composed of one table top and four legs. If one cubic meter of wood can be used to make 50 tables or 300 legs of a square table, and there are 5 cubic meters of wood, how many cubic meters of wood can be used to make the table top and how many cubic meters of wood can be used to make the table legs, and the table top and legs can be made into a square table? How many square tables can be made?

According to the meaning of the question, x + y = 550x × 4 = 300y, the solution is x = 3Y = 2, ∵ 1 cubic meter of wood can make 50 table tops of square table, a square table has a table, ∵ 50x = 50 × 3 = 150. ∵ 150 square tables can be made. Answer: 3 cubic meters of table top, 2 cubic meters of table legs, 150 square tables

1. Family circuit connection method: the lamp, electrical appliances and socket are connected in a single way_ The switch is connected with the lamp Couplet
2. The main parts of home circuit are as follows
(1) A line with a voltage of 220 V to the earth is called a line___ A line that has no voltage with the earth is called a line_ Line.
(2) The function of electric energy meter: to measure the consumption of all electrical appliances .
(3) Two characteristics of fuse material: resistance_ , melting point_ (lead antimony alloy)
3. Safe use of electricity: electric shock accidents in household circuits are all accidents_ Directly or indirectly with Line connected and connected with or For safety, don't Low voltage charged body, do not__ High voltage electrified body

1. Family circuit connection method: the lamp, electrical appliances and socket are connected in a single way___ And__ The switch is connected with the lamp__ String____ Couplet
2. The main parts of home circuit are as follows
(1) A line with a voltage of 220 V to the earth is called a line__ Fire_____ A line that has no voltage with the earth is called a line__ Zero___ Line.
(2) The function of electric energy meter: to measure the consumption of all electrical appliances__ Electric energy__ .
(3) Two characteristics of fuse material: resistance (rate)__ Big___ , melting point__ Low___ (lead antimony alloy)
3. Safe use of electricity: electric shock accidents in household circuits are all accidents___ People____ Directly or indirectly with__ Fire____ Line connected and connected with or__ And the line of fire____ For safety, don't__ Contact____ Low voltage charged body, do not__ Close to__ High voltage electrified body
Back to the sophomore in Senior High School: the resistance must be large, because no matter how large the fuse resistance is, it will not be able to divide the voltage to a great extent. It may divide a little voltage, but it will not affect the use of electrical appliances
Why don't we use copper wire as a fuse? It's because the resistance of copper wire is small and the partial voltage is small, so we can't achieve the function of insurance. So we use lead alloy with high resistivity. If we say that the resistance is high, it's right, because there is the original words in the physics book of grade two

(Zunyi, 2013) now that the car has entered the homes of ordinary people, imagine that you are a driver. When driving at night, you not only need the front lights to have good lighting, but also can reasonably judge the lighting condition. If there is a curve ahead, the lighting condition on the road is ()
A. The illumination condition remains unchanged B. the light moves from the middle of the road to the side of the road C. the light leaves the road D. the illumination distance becomes shorter

When a curve appears at night, because the light beam from the car propagates along a straight line, the light from the car moves from the middle of the road to the side of the road

1. A car moves in a straight line at a constant speed of 1200 meters in 60 seconds. The speed of the car is 1200 meters per second
The physical meaning of this speed is the distance the car passes per second
2. When a pedestrian walks 40 meters in 20 seconds, what is the walking speed
3. The speed of a jumbo jet is 250 meters per second. How many meters does it fly in 600 seconds

①20
② Known; the total distance and time traveled by pedestrians
Pedestrian walking speed
Solution: v = s / T = 40 / 20 = 2m / S
③ Known; the speed and time of flight of an aircraft
Total flight distance
Solution s = VT = 250 × 600 = 150000 M = 150 km

1. In order to verify that the quality of the ice remains unchanged after melting into water, Xiao Yu first measured the quality of the ice, and then put the ice into an open flask to heat, until the water boils, he then measured the quality of the water, but the measurement results show that the quality of the water has decreased, can you find out the reason for the decrease?
2. The quality of rice, vegetables and fruits should be measured in daily life. Do you know what measuring tools are used to measure the quality of gold in jewelry stores?

1. When the water boils, some of it will evaporate (even if it is not boiled, it will evaporate faster)
2. When buying vegetables, we use a bar scale. The accuracy is not so high. When measuring gold, we use a tray scale with an accuracy of 0.01g

How to understand for (expression 1;; expression 3)