1. The radio wave received by the radio propagates into the medium with refractive index of 3 through vacuum. According to V = v3× 10m/s, the propagation speed becomes _ _ _ _ _ _ _ .3x10m/s.

2. The wavelength of electromagnetic wave is 30km, and it takes 1.3s for electric wave to propagate from the earth to the moon. How many waves can this distance fill?

Answer: 1.3× 10.

Analysis: When the propagation speed of waves from the earth to the moon is regarded as the speed of light, the distance from the earth to the moon is S = vt = CT = 1.3× 348cn8.

s 1.3×3× 108

4× 10m。 Wave number n = 1.3× 10. 4λ 3× 108.

3. There is a positively charged static point charge somewhere in (1) space. Is there a magnetic field around it? Why?

(2) If there is a constant current somewhere in space, is there a magnetic field around it? If so, what kind of magnetic field is it?

(3) What are the chances of turning off the lights or hitting people while watching TV? Why?

Answer: (1) There is an electrostatic field around the static point charge. Because the electric field is stable, there is no magnetic field around. (2) There is a constant magnetic field around. (3) You will see TV image jitter and hear noise in the sound, because electromagnetic waves will be emitted when the circuit is turned on or off and the mobile phone is turned on, which will have an impact on the image and sound signals after TV reception.

4. About the electromagnetic field theory, the following statement is correct ().

A the propagation speed of electromagnetic wave in any medium is 3.00×10m/s/s.

There must be a magnetic field in the space around any electric field.

C. After the conductor is electrified, there is a magnetic field around the conductor, but there is no electric field.

D. electromagnetic wave is a substance with energy and can spread in a vacuum.

Answer: d

5. When the fluorescent lamp is started, will it produce a small range of electromagnetic waves? Is there any simple way to prove your judgment? Answer: When the fluorescent lamp is started, a changing electric field can be generated between the moving and static pieces of the starter in the circuit, thus exciting electromagnetic waves. When the fluorescent lamp starts, the radio will make a "click" sound, indicating that the fluorescent lamp will excite electromagnetic waves at this time.

6. A sits in front of the Great Hall of the People 60 m listening to the report, and B sits at home 5 m away from the TV set listening to the TV broadcast. It is known that the distance from B to the Great Hall of the People 1 000 km, regardless of other factors, then (the speed of sound in the air is 340 m/s) ().

A.a. heard the sound first. B.b. heard the sound first. C. A and b hear D. uncertain answer: B.

60m 1 000km analysis: the time required for sound to reach A is t 1 = = 0. 176s, and the time required for sound to reach B is t2340m/s30000km/s.

5m=0.0 18s。 340 m/s

eight

7. Regarding electromagnetic waves, the following statement is true ().

A. In a vacuum, the higher the frequency, the greater the propagation speed of electromagnetic waves.

B In a vacuum, the greater the energy of electromagnetic waves, the faster their propagation speed.

C. When electromagnetic waves enter the medium from vacuum, the speed becomes smaller and the frequency remains unchanged.

D. As soon as the electromagnetic oscillation of the transmitting circuit stops, the generated electromagnetic wave disappears immediately.

Answer: c

8. The phenomenon of electromagnetic induction reveals the internal relationship between electricity and magnetism. According to this discovery, people invented many electrical appliances. Which of the following appliances does not use the principle of electromagnetic induction ()?

A. dynamic microphone B. incandescent bulb C. tape recorder D. fluorescent lamp ballast

Answer: b

Analysis: The voice coil in the moving-coil microphone vibrates in the magnetic field of the permanent magnet, resulting in induced current. When the tape recorder records, the sound causes the microphone to generate an induced current that varies with the sound. When playing, the changing magnetic field on the magnetic tape causes an induced current in the playback head coil. When the switch is turned on, the fluorescent lamp ballast generates instantaneous high voltage. All three are based on the principle of electromagnetic induction, while incandescent bulbs are not.

9. According to Maxwell's electromagnetic field theory, the following statement is wrong ().

A. A constant magnetic field is generated around a constant electric field, and a constant electric field is generated around the constant magnetic field.

B. generate a magnetic field around the changing electric field, and generate an electric field around the changing magnetic field.

C, generating a uniform magnetic field around the uniform electric field, and generating a uniform electric field around the uniform magnetic field.

D, generating a stable magnetic field around the uniformly changing electric field, and generating a stable electric field around the uniformly changing magnetic field.

Answer: AC

Maxwell: British physicist. Main contributions: The probability distribution theory and electromagnetic field theory of molecular motion velocity are established. Established the famous Cavendish laboratory. Maxwell systematically summarized the previous research results, and successively published "On the lines of physical force" and "Theory of electromagnetic field dynamics", which declared the establishment of a complete electromagnetic field theory with a set of electromagnetic field equations of Maxwell equations. Maxwell believes that the essence of this phenomenon is that the changing magnetic field produces an electric field in space. If there is a closed circuit, the free charge in the circuit will move directionally under the action of this electric field, forming a current; Even if there is no circuit in the changing magnetic field, an electric field will be generated in space.

Hertz is a German physicist, 1857 was born in Hamburg on February 22nd. At school, he was attracted by optical and mechanical experiments. 1878, he transferred to Berlin university. 1879 achieved excellent results in the physics competition and won the gold medal. The following year, he received a doctorate and became Helmholtz's assistant. 1885, he was a professor of physics at Karlsruhe Institute of Advanced Technology. 1889, he succeeded Clausius as a professor of theoretical physics at Bonn University. In the same year, he was elected as a member of the Communication Department of Berlin Academy of Sciences. Hertz's main contribution to physics is that he successfully proved the existence of electromagnetic waves by experiments and perfected Maxwell's electromagnetic field theory. Maxwell's work on electromagnetic field theory was deeply influenced by Faraday. He is convinced of Faraday's thought and determined to provide the foundation of mathematical method for Faraday's field concept. Especially when he was teaching at the Royal College in London, he had the opportunity to visit Faraday, which strengthened his belief. Young Maxwell, with his excellent mathematical ability and strict logical reasoning, highly summarized Faraday's intuitive electromagnetic field theory, summarized the research results of electromagnetism at that time, established the electromagnetic field equation and established the electromagnetic field theory.

Maxwell (183 1~ 1879) is a British theoretical physicist and mathematician. 183 1 June 13 was born in Edinburgh, England. His father is a scientist. He was influenced by science since he was a child. /kloc-at the age of 0/5, he submitted a mathematical paper to the Royal Society of England and published it in the Journal of the Royal Society of Edinburgh, which showed his outstanding talent for the first time. 1847 was admitted to the University of Edinburgh to study mathematics and physics. 1850 transferred to Cambridge university, 1854 stayed in school after graduation. From 1856 to 1865, he taught at the University of Aden and Royal College London. 187 1 year, Maxwell is the director of Cambridge physics laboratory. 1874, the Cavendish laboratory he presided over was built and became the first director of the laboratory. 1879165438+1On October 5th, Maxwell died in Cambridge.

After that, Hertz designed an experiment to reflect electromagnetic wave with zinc plate, and calculated the wave velocity of electromagnetic wave by using the standing wave wavelength generated by the superposition of incident wave and reflected wave and the oscillation frequency of the generator. The final calculation result is exactly the same as Maxwell expected-equal to the speed of light. Hertz also confirmed through experiments that electromagnetic waves are shear waves, which have all the characteristics of light waves: they can produce reflection, refraction, diffraction, interference and polarization, thus comprehensively verifying the correctness of the electromagnetic theory of light. 1890, hertz sorted out Maxwell's theory, further improved Maxwell's equations, made them more beautiful and symmetrical, and became the modern form of Maxwell's equations. Hertz also discovered the photoelectric effect for the first time, which later became the experimental basis for Einstein to establish the quantum theory of light.

1888 10, Hertz did a spark discharge experiment with a discharge coil in the physics laboratory of Karlsruhe Institute of Advanced Technology, and accidentally found that the insulated coil near the other opening of the discharge coil had electric spark jumping. This caught his attention and immediately reminded him that Helmholtz had asked him to study and verify Maxwell's electromagnetic field theory. He designed a device to carry out the experiment. He connected a 30 cm long copper bar A and B to the two electrodes of the induction coil C. One end of each copper bar was connected to a brass ball, and the other end was connected to a square brass piece with a side length of 40 cm, so that the two brass balls were opposite to each other to form a generator. When electrified, high-frequency oscillation sparks are generated between the copper balls of the generator. In addition, he bent a metal wire into a ring and connected a copper ball at both ends as a detector (pictured above). The detector is 0/0 meter away from the electromagnetic wave generator. When an electric spark was generated between the two copper balls of the generator, he also saw an electric spark generated between the two copper balls of the detector. Hertz successfully proved the existence of electromagnetic waves with such a simple instrument. Hertz's experimental report caused a sensation in the scientific community.

Hertz died of bone cancer on New Year's Day on 1894 at the age of 37. Helmholtz, his mentor, praised him as "brilliant and persevering, and used his short life to solve a series of important problems that many scientists have not solved in a century". Hertz's experiment has opened up a new road for the development of radio technology, and he is known as the forerunner of radio communication. Later generations named the frequency unit after him in memory of him.

1. All electromagnetic waves in vacuum have the same () answer: C.

A. frequency B. wavelength C. wave velocity D. energy

2. About the characteristics of electromagnetic waves, the following statement is incorrect ().

A. The electric field and magnetic field in electromagnetic waves are perpendicular to each other, and electromagnetic waves propagate in mutually perpendicular directions.

B. electromagnetic waves are shear waves.

C electromagnetic wave propagation does not need medium, but mutual induction of electric field and magnetic field.

D. electromagnetic waves have no interference and diffraction.

Answer: d

3. About electromagnetic theory, the following statement is correct ()

A. a magnetic field is bound to be generated around the electric field, and an electric field is bound to be generated around the magnetic field.

B. A changing magnetic field is bound to be generated around the changing electric field, and a changing electric field is bound to be generated around the changing magnetic field.

A uniformly changing magnetic field is bound to be generated around a uniformly changing electric field.

A periodically changing magnetic field must be generated around the periodically changing electric field.

Analysis: According to Maxwell's electromagnetic theory, only a changing electric field can produce a magnetic field, a uniformly changing electric field can produce a stable magnetic field, and a periodically changing magnetic field can be produced around a periodically changing electric field. Answer: d

4. For electromagnetic waves and mechanical waves, the following statement is correct ()

A. electromagnetic waves and sound waves are longitudinal waves.

B. When air enters the water and propagates, the propagation speed of electromagnetic wave decreases and the propagation speed of sound wave increases.

C electromagnetic wave is transverse wave, and mechanical wave can be longitudinal wave.

D the propagation speed of mechanical waves is determined by the medium, and the propagation speed of electromagnetic waves in the medium is not only related to the medium, but also related to the frequency of electromagnetic waves.

Analysis: Electromagnetic waves are shear waves, and some mechanical waves can be longitudinal waves and mechanical waves.

The propagation speed is determined by the medium, and the propagation speed of electromagnetic waves in the medium is not only related to

It is related to the frequency of medium and electromagnetic wave. Answer: BCD.

5. About electromagnetic waves and mechanical waves, the following statement is true ()

A. Electromagnetic waves propagate far from the occurrence area, and mechanical waves propagate far from the vibration of the vibration source.

B electromagnetic wave propagation does not need medium, but mechanical wave propagation needs medium.

C. mechanical waves and electromagnetic waves are essentially the same.

D. Can they all reflect? Refraction? Interference and diffraction phenomena

Analysis: Mechanical waves are generated by vibration, and propagation requires medium. Electromagnetic waves are generated by periodically changing electric fields (or magnetic fields), but they do not need a medium for propagation. Electromagnetic waves and mechanical waves are different in nature, but they all have the characteristics of waves. Answer: ABD

(2) Hertz observed that when there is a spark jump between two metal balls in the induction coil, there is also a spark jump between two small balls in the wire loop. According to this experiment, Hertz captured the electromagnetic waves in human history for the first time.

(3) In later experiments, Hertz observed the reflection of electromagnetic waves? Refraction? Interference? Polarization and diffraction, and it is proved by measurement that the speed of electromagnetic wave in vacuum is C, so Hertz confirms Maxwell's electromagnetic theory.

(4) The experiment of Hertz paved the way for the development of radio technology. Later, in order to commemorate him, people set the unit of frequency as Hertz.

Three? Hertz experiment

Maxwell predicted the existence of electromagnetic waves,

But he didn't see the scientific experiment about electromagnetic wave theory.

Prove Turn the predictions of genius into universal recognition.

This fact is attributed to the German scientist Hertz.

(1) Hertz experimental device

Electromagnetic waves are shear waves. E and b at any point in the propagation direction change sinusoidally with time, and e and b are perpendicular to each other and to the propagation direction. The propagation of electromagnetic waves does not need medium, and the propagation speed of electromagnetic waves in vacuum is the same as the speed of light, that is, c = 3.00×108m/s. Electromagnetic waves have the property of * * and can interfere? Diffraction and other phenomena, can electromagnetic waves be reflected when interacting with matter? Absorb? Refraction and other phenomena. The propagation speed of electromagnetic wave in vacuum satisfies the wave velocity formula c = λ f, and when the same electromagnetic wave propagates in different media, the frequency is constant (the frequency is determined by the wave source), and the wave velocity is? Wavelength change. The propagation speed in medium is slower than that in vacuum. When electromagnetic waves with different frequencies propagate in the same medium, the propagation speed is different. The higher the frequency, the smaller the wave velocity, the lower the frequency and the greater the wave velocity.

If there is a periodically changing electric field in a certain area of space, then this periodically changing electric field will produce a periodically changing magnetic field in its surrounding space; This periodically changing magnetic field produces a new periodically changing electric field in its surrounding space. The changing electric field and the changing magnetic field are interrelated to form an inseparable unity, which is the electromagnetic field. The changing electric field and the changing magnetic field are always generated alternately and propagate from the generating area to the surrounding space, and the electromagnetic field propagating from the generating area to the distance is electromagnetic wave.

1. Change the magnetic field to generate electric field:

(1) When a closed circuit is placed in a changing magnetic field, an induced current will be generated in the circuit, as shown in Figure A below.

(2) Maxwell's phenomenon: there is induced current in the loop, which must be the electric field generated by the changing magnetic field, and the free electrons move directionally under the action of the electric field.

(3) Maxwell's first hypothesis is that even if there is no closed circuit around the changing magnetic field, an electric field will still be generated, which is a universal law, as shown in Figure B above.