Tóm tắt lý thuyết Vật lý 12 Chương 5 hay nhất

Synthetic Summary of Physics 12 Chapter 5 the best, most complete to help you consolidate knowledge and review better.

Theory of Dispersion of Light

I) Newton’s experiment on the dispersion of light (1672)

Experimental diagram: as shown below

Summary of the best Physics 12 Chapter 5

Experimental results: When sunlight passes through the prism, it is not only deflected to the bottom due to refraction, but also stretched into a colorful band. By carefully examining the color range, we can distinguish colors: red, orange, yellow, green, blue, indigo, purple. However, the boundary between colors is not clear, that is, one color gradually changes to another color continuously.

This band of light is called the spectrum of the Sun. Sunlight is white light.

This phenomenon is called light dispersion (of white light).

II) Explain the phenomenon of light dispersion

To test whether the glass has changed the color of the light. Newton did the following experiment:

Experimental diagram: as shown below. He isolated a yellow light beam in the color band, and then refracted it through a second prism.

Summary of the best 12 Chapter 5 Physics theory (photo 2)

– Experimental results: the light beam is only deflected to the bottom (due to refraction) without changing color.

Monochromatic light is light that has a certain color and is not dispersed, but only deflected when it passes through a prism.

– Polychromatic light is a mixture of two monochromatic lights that become, and are dispersed, when passing through a prism.

– White light is a mixture of many monochromatic lights with a color that varies continuously from red to purple. White light is a case of polychromatic light.

Dispersion of light is the splitting of a polychromatic beam of light into the monochromatic beams that make up it.

– Explain dispersion phenomenon:

+) White light is a mixture of many monochromatic light.

+) The refractive index of glass for monochromatic light of different colors is different, so their angle of deviation when passing through the prism is different, as a result, when coming out of the prism they are no longer coincident. but separated.

– Comment: from the experimental results: red rays deviate the least, violet rays deviate the most, so the refractive index of violet light is the largest, the refractive index of red light is the smallest:

nred orange yellow cyan blue indigo purple

III) Application

– Explain some natural phenomena such as rainbows, etc. After the rain, rainbows often appear because after the rain in the air, there are many tiny water droplets acting as prisms, then sunlight The sky (white light) will be scattered through the water prisms into a rainbow color. So rainbows not only appear after the rain, but also appear in places with a lot of water vapor such as waterfalls, etc.

– Application in spectrometer: analyze a light beam into the monochromatic light beams that make up it.

Theory of interference of light

I) Diffraction of light

Summary of the best Physics 12 Chapter 5 (photo 3)

– Experiment: Using a light source S placed in front of a small round hole O, cut in a closed box. Observe the same light in the opposite city.

– Experimental results: If the light travels straight, there will be a circular light streak on the wall with a diameter of D. But in fact we see a circular light with a diameter of D’ > D. The smaller the O hole, the better D’. much larger than D.

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Diffraction is the phenomenon in which light propagates differently from the straight line when the light encounters an obstacle.

– Explanation of the phenomenon: to explain this phenomenon, let’s admit: each monochromatic light beam is considered as a wave with a definite wavelength.

II) The phenomenon of light interference.

1) Yang’s experiment on interference of light.

Experimental diagram: as shown below

Summary of the best Physics 12 Chapter 5 (photo 4)

Experimental results: In the region where two light beams meet, they should be bright, but we see alternating dark and bright lines. Like interference, it forces us to assume that light is a wave. Dark lines are where two light waves cancel each other out, light lines are where two light waves reinforce each other. The alternating light and dark fringes are called interference fringes of two light waves.

2) Location of light and dark fringes.

* Assuming the wavelength of the interfering light is , the distance between the two slits Sfirst,S2 is a, the distance from the two slits to the screen is D. O is the position of the central bright fringe. Consider a point A that is x 1 distance from O.

Summary of the best Physics 12 Chapter 5 (photo 5)

– Distance from A to source Sfirst To be:

Summary of the best Physics 12 Chapter 5 (photo 6)

– Distance from A to source S2 To be:

Summary of the best Physics 12 Chapter 5 (photo 7)

I have d22 – dfirst2 = (d2 – dfirst)(d2 + dfirst) = 2ax

Since a,x ≪ D, there is d2 + dfirst 2D

Then the difference in the paths of the two light waves from Sfirst,S2 transmitted to A is: d2-dfirst ≈ 2ax/2D = ax/D

* Condition for at A to be a bright fringe: d2 – dfirst = kλ.

The distance from O to the bright fringe of order k is xk = kλD/a (k = 0, ±1, ±2…)

Comment: O position of bright fringe of order 0: k = 0 ↔ x = 0 (∀ λ), so O is called central fringe or central fringe.

* Condition for at A is dark fringe: d2 – dfirst = (k – 1/2)λ

The distance from O to the kth dark fringe is x’k = (k – 1/2)[(λD)/a] (k = ±1, ±2…)

3) Rough range

– Definition: is the distance between two bright fringes, or two consecutive dark fringes.

– Formula to calculate fringe interval i:

i = xk+1 – xk = x’k+1 – x’k = D/a

4) Application:

Measure the wavelength of light. Measure the quantities D,a,i then wavelength: = ia/D

III) Relationship between wavelength of light and color.

The experimental results show:

– Each monochromatic light has a definite wavelength or frequency in a vacuum

Visible light (visible light) has a wavelength in the range: 380÷760 nm.

Table of wavelengths of visible light in a vacuum





Red 640÷760 Blue 450÷510
Orange 590÷650 Indigo 430÷460
Yellow 570÷600 Violet 380÷440
Green 500÷575

– The white light of the Sun is a mixture of countless monochromatic light with wavelengths ranging from 0 to ∞.

– Conditions for the phenomenon of light interference to occur are: two light sources combined

+) two sources must emit two waves of the same wavelength

+) oscillation phase difference of both sources must be constant with time.

Spectral Types Theory

I) Prism spectrometer.

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– Definition: is an instrument used to analyze a complex (polychromatic) light beam into its monochromatic light components.

Working principle: Based on the phenomenon of light dispersion

– Structure: consists of 3 main parts: collimator, dispersion system, dark chamber.

Summary of the best Physics 12 Chapter 5 (photo 8)

+) Collimator: is a tube with a converging lens L_1 at one end, a narrow slit F located at the main focal length of L_1. When light is shone through the collimator, a parallel beam of light is obtained (to ensure that the angle of incidence of all the light is equal).

+) Dispersion system: consists of one (or more) prisms P. parallel polychromatic light beams, after passing through the prism, will be scattered into many parallel monochromatic beams with different deflection angles.

+) Dark chamber (photo booth): Is a light-tight box, one end has a converging lens L_2, the other end places a photographic film (photoglass) placed in the focal plane of L_2. Parallel light beams out of the dispersion system, after passing through L_2, will converge at points on the film called spectral lines.

II) Spectral types:

– Classification: Continuous Spectrum

Emission spectrum

Absorption Spectrum

Spectrum comparison table

Continuous spectrum

Emission line spectrum

Absorption line spectra

Concept A spectrum consisting of many color bands from red to purple, connected in a continuous way Is a system of individual light lines, separated by dark spaces. A continuous spectrum that is missing some colored lines due to absorption by a gas or vapor
For example

Spectrum of sunlight

Summary of the best Physics 12 Chapter 5 (photo 9)

The emission line spectrum of the hydrogen atom

Summary of the best Physics 12 Chapter 5 (photo 10)

Absorption spectrum of hydrogen vapor

Summary of the best Physics 12 Chapter 5 (photo 11)

Source Solids, liquids and gases are heated at high pressure Gas or vapor at low pressure when excited by heat or electricity The temperature of the gas (vapour) must be lower than that of the continuous light source
Nature It does not depend on the nature but only on the temperature of the source. As the temperature increases, the source will gradually emit light with a decreasing wavelength, the higher the temperature, the shorter the wavelength of the lightest region. Each chemical element has a characteristic line spectrum of that element. They differ in the number of lines, the position of the lines (wavelength) and the brightness between the lines. The absorption line spectra are also characteristic for each element. The element that emits light will absorb that light.
Application Measures the temperature of high-temperature luminous objects such as stars through its spectrum To analyze the structure of substances To analyze the structure of substances

Theory of Infrared, Ultraviolet, and X-Rays. Electromagnetic Wave Scale

I) Non-visible radiations:

Experiments have shown that in addition to the visible light region, there are radiations that are not visible, but also have thermal effects, which also obey the laws of propagation, reflection, and refraction, and also cause interference. radiation, interference like visible radiation. eg: infrared, ultraviolet, x-ray.

Comparison table of invisible radiation

Infrared rays

Ultraviolet rays

X-Rays (Rhengen Rays)

Concept Is invisible radiation with wavelengths from 0.76 μm to several mm. Is invisible radiation with wavelengths from 0.38 μm to about 10-9m. Is radiation with wavelengths from 10-8m to 10-11
Source All objects with a temperature greater than 0(K) or -273℃

Objects with high temperature (from 2000℃ and above)

For example: electric arc, Sun, mercury vapor lamp.

Every time a cathode beam (a beam of high-energy electrons) strikes a solid object, the object emits X-rays.

The thermal effect is the most prominent property. Objects that absorb infrared rays will heat up.

– Capable of causing some chemical reactions, may affect film.

– Can be modulated like high-frequency electromagnetic waves.

– Induces the photoelectric effect in some semiconductors.

– Effects on movies

– Stimulates the luminescence of many substances.

– Stimulates many chemical reactions

– Ionize the air and many other gases

– Has biological effects: destroys cells, kills bacteria and fungi, is a precursor for vitamin D synthesis

– May cause photoelectric effect.

– Strongly absorbed by water and glass, but can pass through quartz. In addition, the ozone layer absorbs all rays with wavelengths below 300 nm and is an armor to protect organisms on Earth.

The most outstanding property is the ability to penetrate paper, fabric, wood, even metal. X-rays with shorter wavelengths can penetrate deeper or harder.

– Strong effect on photo glass.

– Ionizing the air.

– Luminescence of some substances.

Strong physiological effects: destroy cells, kill bacteria, …

Causes photoelectric effect in most metals.


– Drying, heating, cooking.

– Take pictures at night, take pictures of many celestial bodies, take pictures of the earth from satellites.

– Used in remote controls (television controls, air conditioners, …)

– Military: infrared binoculars for night vision and driving, infrared cameras for night photography and video recording, missiles that automatically find targets based on infrared rays emitted by the target.

– Medicine: used to sterilize surgical instruments, treat rickets.

Food industry: food sterilization.

– Mechanical industry: find about cracks (defects) on the surface of the product.

– Medicine: used for electric irradiation, crazy imaging, superficial cancer treatment.

– Industry: check the quality inside the product.

– Traffic: Check passengers’ luggage

– Laboratory: Studying the structure of solid bodies

II) Electromagnetic wave scale:

– Radio waves, infrared rays, visible light, ultraviolet rays, X-rays, gamma rays (radioactive rays) all have the same nature as electromagnetic waves. The difference in frequency (wavelength) of the types of electromagnetic waves leads to the difference in their properties and effects.

Electromagnetic wave scale

Summary of the best Physics 12 Chapter 5 (photo 12)

Posted by: Trinh Hoai Duc High School

Category: Grade 12, Physics 12

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