It is easy to learn knowledge, but difficult to turn it into ability; It is easy to ask questions, but difficult to get satisfactory answers; It is easier to comment on others than to do it on the spot; It is easy to blame colleagues, but difficult to evaluate yourself correctly. Below I will share with you three knowledge points of physics elective courses in senior high school, hoping to help you!

Directory high school physics knowledge points

Senior three physics elective knowledge points

Summary of three knowledge points in senior high school physics elective course

Law of conservation of momentum in high school physics knowledge points

First, the momentum; law of conservation of momentum

1. Momentum: Momentum can be defined or explained in two aspects:

The product of the mass and velocity of an object is called the momentum of the object.

② Momentum is a measure of the mechanical motion of an object.

The expression of momentum P=mv. The unit is. Momentum is a vector, and its direction is the direction of instantaneous velocity. Because speed is relative, so is momentum.

2. Law of Conservation of Momentum: When the system is not subjected to external force or the resultant force of external force is zero, the total momentum of the system is conserved. The law of conservation of momentum has many expressions according to the actual situation. Generally, the equal sign is used to represent the total momentum of the system before and after the action.

When applying the law of conservation of momentum, we should pay attention to the following questions:

① The law of conservation of momentum is generally aimed at the object system, but it is meaningless for a single object.

(2) Aiming at some specific problems, such as collision and explosion. In a very short time, the interaction between objects in the system is far greater than the external force they are subjected to, so these objects can be regarded as a system with zero external force and follow the law of conservation of momentum in this very short time.

(3) When calculating momentum, speed should be involved. At this time, the speed of each object in an object system must be relative to the same inertial reference frame, generally taking the ground as the reference object.

④ Momentum is a vector, so "total momentum of the system" refers to the vector sum of the momentum of all objects in the system, not the algebraic sum.

⑤ The law of conservation of momentum can also be applied to the case of fractional momentum conservation. Sometimes, although the resultant force acting on the system is not equal to zero, as long as the resultant force component of a certain aspect is zero, the component of the total momentum of the system in this direction is conserved.

⑥ The law of conservation of momentum has a wide range of applications. As long as the system is free from external force or the resultant force is zero, the law of conservation of momentum is applicable to the interaction of all objects in the system, whether it is gravity, elasticity, friction, electricity, magnetism and so on.

When the objects in the system interact, no matter the direction of motion is the same or opposite; No matter direct contact or no contact in the process of interaction; The law of conservation of momentum also applies whether they stick together or break into pieces after interaction.

3. Comparison of momentum and kinetic energy, law of conservation of momentum and law of conservation of mechanical energy.

Comparison of momentum and kinetic energy;

Momentum is a vector and kinetic energy is a scalar.

② Momentum is a physical quantity used to describe the mutual transmission of mechanical motion, while kinetic energy is often used to describe the mutual transformation between mechanical motion and other motions (such as heat, light, electricity, etc.). ).

For example, the completely inelastic collision process studies the transmission of mechanical motion-the change of speed can be conserved by momentum, and if we want to study the mechanical energy converted into internal energy during collision, we must calculate the kinetic energy as loss. Therefore, momentum and kinetic energy are physical quantities that reflect and describe mechanical motion from different sides.

Compared with the law of conservation of mechanical energy, the law of conservation of momentum has a wider scope of application, while the law of conservation of mechanical energy has a much narrower scope of application. These differences must be paid attention to in use.

4. Collision: The phenomenon that two objects interact with each other for a very short time, with great force, and other influences are relatively small, and the motion state becomes obvious is called collision.

In the form of collision between objects, it can be divided into "centripetal collision" (frontal collision), the connection line of the velocity of objects before collision along their center of mass; "Inconsistent collision"-I didn't learn it in middle school.

According to whether the total kinetic energy of two objects changes before and after collision, it can be divided into "elastic collision" Conservation of total kinetic energy of object system before and after collision; "Inelastic collision", completely inelastic collision is a special case of inelastic collision. In this kind of collision, the objects stick together after collision, and the kinetic energy loss is the greatest.

All kinds of collisions obey the law of conservation of momentum and energy, but in inelastic collisions, some kinetic energy is converted into other forms of energy, so kinetic energy is not conserved.

Wave-particle duality of three knowledge points in senior high school physics elective course

First, quantum theory

1. Create a symbol: 1900, Planck published a paper on the energy distribution law of normal spectrum in the German Yearbook of Physics, which marked the birth of quantum theory.

2. The main content of quantum theory

(1) Planck believes that the radiant energy of matter is not infinitely separable, and its smallest indivisible energy unit is "energy quantum" or "quantum", that is, the unit that constitutes energy is quantum.

(2) The radiant energy of matter is not continuous, but changes by leaps and bounds in an integer multiple of quantum.

3. The development of quantum theory

(1)1905, the quantum concept of Einstein Prize was extended to the propagation of light, and the quantum theory of light was put forward.

② In1913, British physicist Bohr extended the concept of quantum to the internal energy states of atoms, and proposed a quantized atomic structure model, which enriched the quantum theory.

③ At around 1925, quantum mechanics was finally established.

Second, blackbody and blackbody radiation

1. Thermal radiation phenomenon

Any object will emit electromagnetic waves of various wavelengths at any temperature, and its radiation energy and its distribution according to wavelength are related to temperature. The phenomenon that molecules and atoms in matter emit electromagnetic waves due to thermal excitation is called thermal radiation.

Objects radiate energy at any temperature.

(2) Objects not only radiate energy, but also absorb it. The stronger an object's ability to emit electromagnetic waves in a certain frequency range, the stronger its ability to absorb electromagnetic waves in that frequency range.

When radiation and absorbed energy are just equal, it is called thermal balance. At this time, the temperature is constant.

Experiments show that the radiation energy of an object depends on its temperature (T), radiation wavelength, time and emission area.

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Objects have the ability to radiate energy to the surroundings and absorb energy radiated from the outside. A blackbody is an object that absorbs all radiation at any wavelength at any temperature.

3. Experimental rules:

① With the increase of temperature, the radiation intensity of blackbody increases;

(2) With the increase of temperature, the maximum radiation intensity moves to the short wave direction.

Third, photoelectric effect.

1. photoelectric effect Under the irradiation of light (including invisible light), the phenomenon that an object emits electrons is called photoelectric effect.

(1) Any metal has a limit frequency, and the frequency of incident light must be greater than this limit frequency to produce photoelectric effect, while light below this limit frequency cannot produce photoelectric effect.

② The maximum initial kinetic energy of photoelectrons has nothing to do with the intensity of incident light, but the light increases with the increase of incident light frequency.

(3) When the light with frequency greater than the limit irradiates the metal, the light current intensity (reflecting the number of photoelectrons emitted per unit time) is directly proportional to the incident light intensity.

(4) When the metal is irradiated, the photoelectron emission generally does not exceed 10-9 seconds.

2. The difficulty of wave theory in photoelectric effect.

Wave theory holds that the energy of light, that is, the intensity of light, is determined by the amplitude of light waves and has nothing to do with the frequency of light, so wave theory has difficulties in explaining the above experimental laws.

Summary of three knowledge points in senior high school physics elective course I. Nuclear structure model

1, the discovery of electrons and Thomson's atomic model;

Discovery of (1) electron:

1897, the British physicist Thomson conducted a series of studies on cathode rays, thus discovering electrons.

The discovery of electrons shows that atoms have a fine structure, thus breaking the concept that atoms are inseparable.

2 Thomson's atomic model:

1903, Thomson imagined that the atom is a charged ball, and its positive charge is evenly distributed throughout the ball, while the negatively charged electrons are embedded in the positive charge.

2. Particle scattering experiment and nuclear structure model.

⑴ Particle scattering experiment: 1909, completed by Rutherford and his assistants Geiger and meston.

① Device: as shown below.

② Phenomenon:

A. Most particles still move in the original direction after passing through the gold foil without deflection.

B. some particles deflect at a large angle.

C few particles with deflection angle over 90, some almost reach 180, that is, they are bounced back in the opposite direction.

(2) Nuclear structure model of atom:

Because the mass of particles is more than 7000 times that of electrons, electrons will not obviously change the direction of particle motion, and only positive charges in atoms can obviously affect the motion of particles.

If the distribution of positive charges in atoms is as uniform as Thomson model, and the positive charges acting on particles passing through gold foil are balanced in all directions, then the motion of particles will not change obviously. The phenomenon of scattering experiment proves that the positive charges in atoms are not evenly distributed in atoms.

19 1 1 year, Rutherford put forward a nuclear structure model through the analysis and calculation of particle scattering experiments: there is a small nuclear nucleus in the center of the atom, called the nucleus, which concentrates all the positive charges and almost all the masses of the atom, and negatively charged electrons rotate around the nucleus in the outer space of the nucleus.

The nuclear radius is about 10- 15m, and the atomic orbital radius is about 10- 10m.

(3) Spectrum

(1) to observe the spectrum of the instrument, spectroscope.

② Classification, generation and characteristics of spectra

③ Spectral analysis:

An element emits light with some characteristic wavelengths at high temperature and absorbs light with these wavelengths at low temperature. Therefore, bright lines in bright light waves and dark lines in absorption spectra are called characteristic spectral lines of this element, which are used for spectral analysis.

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