Talk about the knowledge about current, voltage, resistance and Ohm theorem in the second semester of junior high school physics, and how to analyze the circuit,

Talk about the knowledge about current, voltage, resistance and Ohm theorem in the second semester of junior high school physics, and how to analyze the circuit,

1. About current and other knowledge, this topic is wide. Here is my experience
(1) We can learn current, voltage and resistance together, because these three physical quantities are the most basic physical quantities in junior high school physics (electricity). The relationship between them can be obtained from Ohm's theorem (I = u / R; u = IR; r = u / I. but we should pay attention to the one-to-one correspondence. In these formulas, these three physical quantities are all for the same conductor)
(2) Junior high school of these three physical quantities are relatively simple, from the series, parallel point of view to compare them together
Series circuit: I total = I1 = I2 =.; u total = U1 + U2 +; R total = R1 + R2 +
The total voltage is equal to the sum of the voltages at both ends of the consumers, and the total resistance is equal to the sum of the resistances of the consumers
Parallel circuit: I total = I1 + I2 +; u total = U1 = U2 =; 1 / R total = 1 / R1 + 1 / r2 +
In the parallel circuit, the current in the main circuit is equal to the sum of the currents in each branch, the total voltage is equal to the voltage at both ends of each branch, and the reciprocal of the total resistance is equal to the sum of the reciprocal of the resistances in each branch
2. It's difficult for beginners to analyze circuits
(1) First of all, analyze whether the circuit is a series circuit or a parallel circuit. There are many ways to judge, I generally use the current method. That is to say, to see whether the current in the circuit has shunt. If there is only one way, it is a series circuit. If there are multiple ways, it is a parallel circuit
(2) Then look at the ammeter and voltmeter in the circuit. If the ammeter is connected in series, it will measure the current passing through; if the voltmeter is connected at both ends, it will measure the voltage at both ends
(3) Other components, such as the function of sliding rheostat in the circuit, whether the switch is single throw or double throw, should be seen clearly

Shanghai Science and Technology Press

Elasticity, gravity, friction, simple machinery, pressure, buoyancy, work, mechanical efficiency, that's all. It's not very difficult!

All the calculation formulas and knowledge points in the first to eighth chapters of the second volume of physics pep
Collation of calculation formula, prototype and deformation formula of each formula

1、 Ohm's law part
1. I = u / R (Ohm's Law: the current in a conductor is directly proportional to the voltage at both ends of the conductor and inversely proportional to the resistance of the conductor)
2．I=I1=I2=… =In (characteristic of current in series circuit: current is equal everywhere)
3．U=U1+U2+… +UN (characteristics of voltage in series circuit: in series circuit, the total voltage is equal to the sum of voltage at both ends of each circuit)
4．I=I1+I2+… +In (the characteristic of current in parallel circuit: the current on the main circuit is equal to the sum of the currents in each branch circuit)
5．U=U1=U2=… =UN (characteristics of voltage in parallel circuit: the voltage at both ends of each branch is equal to the power supply voltage)
6．R=R1+R2+… +RN (characteristic of resistance in series circuit: the total resistance is equal to the sum of resistance of each part of the circuit)
7．1/R=1/R1+1/R2+… +1 / RN (the characteristic of resistance in parallel circuit: the reciprocal of total resistance is equal to the sum of the reciprocal of each parallel resistance)
8. R union = R / n
9. R series = NR (formula for calculating total resistance when n identical resistors are in series)
10. U1: U2 = R1: R2 (relationship between voltage and resistance in series circuit: the ratio of voltage is equal to the ratio of their corresponding resistance)
11. I1: I2 = R2: R1 (relationship between current and resistance in parallel circuit: the ratio of current is equal to the inverse ratio of their corresponding resistance)
2、 Electric power part
12. P = UI (empirical formula, suitable for any circuit)
13. P = w / T (definition, suitable for any circuit)
14. Q = i2rt (Joule's law, suitable for any circuit)
15．P=P1+P2+… +PN (suitable for any circuit)
16. W = uit (empirical formula, suitable for any circuit)
17. P = I2R (compound formula, only suitable for pure resistance circuit)
18. P = U2 / R (compound formula, only suitable for pure resistance circuit)
19. W = q (empirical formula, only suitable for pure resistance circuit, where W is the work done by the current flowing through the conductor and Q is the heat generated by the current flowing through the conductor)
W = i2rt (compound formula, only suitable for pure resistance circuit)
21. W = u2t / R (compound formula, only suitable for pure resistance circuit)
22. P1: P2 = U1: U2 = R1: R2 (the relationship between electric power and voltage and resistance in series circuit: in series circuit, the ratio of electric power is equal to the ratio of voltage and resistance)
23. P1: P2 = I1: I2 = R2: R1 (the relationship between electric power and current and resistance in parallel circuit: in parallel circuit, the ratio of electric power is equal to the ratio of their corresponding current and the inverse ratio of their corresponding resistance)

What is a bivariate equation
Good answer and reward
What is the highest power? It's easier to write a formula for the square than to write a formula for the square

An equation with one unknown and the highest power of the unknown is square
X² -2X=-1
X²-2X+1=0
(x-1) 2 = 0 the 2 outside the brackets is the square
X=1
X & sup2; is the highest order term

A long time ago, how much land area did China have

The largest area of China was in the Yuan Dynasty. It reached the east coast of the Pacific Ocean in the East, the Arctic Ocean in the north, Budapest, the capital of Hungary in Europe, occupied Moscow, where the eldest grandson of Genghis Khan established the chinchi Khanate. In the Middle East, xuliewu, the grandson of Genghis Khan, destroyed the Arab Empire, occupied Baghdad, and established the ilikhanate, Only South Asia has not been conquered. Its area should be more than 35 million square kilometers

Newton and the law of gravitation

Newton and the law of gravitation
In 1661, at the age of 19, Newton entered Trinity College of Cambridge University as a fee reducing student. He paid his tuition by doing chores for the college. He became a scholarship winner in 1664 and a bachelor's degree in 1665
In the middle of the 17th century, the education system of Cambridge University was permeated with a strong smell of Scholasticism in the middle ages. When Newton entered Cambridge, he still taught some scholasticism courses, such as logic, ancient prose, grammar, ancient history, theology and so on. Two years later, a new atmosphere appeared in Trinity College. Lucas created a unique lecture, stipulating the teaching of natural science knowledge, Such as geography, physics, astronomy and mathematics. "
Influenced and cultivated by mathematics and Natural Science in Cambridge, Newton had a strong interest in exploring natural phenomena, and the quiet environment of his hometown made his thoughts soar. The short period from 1665 to 1666 became the golden age of Newton's scientific career. He was full of ideas and talents in the field of natural science, thinking about problems never thought before, Stepped into the field that predecessors did not involve, created unprecedented amazing performance
At the beginning of 1665, Newton established the series approximation method and the rule of converting the binomial of any power into a series; in November of the same year, he established the positive current number method (differential); in January of the next year, he studied the color theory with prism; in May, he began to study the counter current number method (integral), He also deduced from Kepler's law that the force that keeps the planets in their orbit must be inversely proportional to the square of the distance from them to the center of rotation. Newton realized the legend of the earth's gravity when he saw the apple landing, which is also an anecdote at this time
In a word, during the two years of living in his hometown, Newton devoted more energy to scientific creation than ever before, and concerned about natural philosophy. His three great achievements: calculus, gravitation and optical analysis were all born and formed at this time. It can be said that Newton had begun to describe the blueprint of most scientific creation in his life
Shortly after Easter in 1667, Newton returned to Cambridge University. On October 1, he was elected as the junior member of Trinity College. On March 16, the next year, he received his master's degree and became the senior member of the college. On October 27, 1669, barrow resigned his professorship in order to promote Newton. At the age of 26, Newton was promoted to mathematics professor, Barrow opened the way for Newton's scientific career. Without the help of Newton's uncle and barrow, Newton would not have galloped on the road of science. Barrow made a good story in the history of science

If October happens to have four Sundays, what day is October 31?
20 early reward, 15 late reward (see accuracy added)
1. On the 2nd and 3rd floors, what is the answer

Suppose that the 31st is Sunday, then 24, 17, 10 and 3 are also Sundays
Suppose that the 31st is Monday, then 23, 16, 9 and 2 are also Sundays
Assuming that the 31st is a Tuesday, then 22, 15, 8 and 1 are also Sundays
So it can't be Sunday, one, two

There are two kinds of milk. The first kind is 400 ml, 4 yuan per box. The second kind is 500 ml, 9 yuan per box. That kind of milk is cheap

A:
4000 / 4 = 1000 (ml / yuan)
5000 / 9 is about 556 (ml / yuan)
1000〉556
A: the second kind of benefits

3/13×1001—198÷198198/199

3/13×1001—198÷198198/199
=3/13×1001—198×199/198198
=3/77—199/1001
=231—199/1001
=230 802 / 1001

Is it necessary to prepare a classic example book for high school mathematics?
To enter the first round of review, in the face of many mathematical problems, is it necessary to record them? What are the benefits? Will the effect be obvious? How can I sort them out?

This is absolutely necessary. This is an important review material for entering the review stage in the future. In my opinion, the effect is obvious. The college entrance examination is nothing more than these types of questions. Entering senior three, I think the wrong question book is also very important. Some people cut off the questions on the materials and stick them on the book. I think you should write them yourself. In this process