Physics in the second year of junior high school: sound phenomena and light phenomena

Such a topic would not make sense.

Thought to solve, the result is to solve the problem

You should at least say which place you want to ask.

At first it was low, and then it was pitched higher. Illustrates that the change in sound is related to the frequency of the object's vibration. At the beginning, the air column is long and vibrates slowly, and the pitch is low.

Later, the air column becomes shorter, vibrates faster, and the tone is higher. Design an experiment by pouring water into a boiling water bottle and listening directly to its pitch. Or you can observe the relationship between the distance of the flute hole and the tone of the blow, and the same reason.

Characteristics of sound change: pitch from low to high.

Reason: The column of air in the water bottle is very long at the beginning, the frequency of the vibration is slow, so the pitch is low;

After that, the air column is short, the screen rate of vibration is fast, and therefore the tone is high.

Experiment: Xiao Ming blows a flute made of a plastic straw with the same force, and keeps it short, and will find that the tone goes from low to high.

Reason: At the beginning, the air column in the bottle was long, the vibration was slow, and the sound was lowered; Later, the air column was short, the vibration was fast, and the sound was turned up.

Description: The pitch gradually rises and the loudness decreases.

Reason: The water poured into the bottle lifts the gas above, and due to the small mouth of the bottle, the gas compresses and vibrates to produce a sound. As the water rises, the air column becomes shorter and shorter, the vibration frequency increases, and the space becomes smaller, so the vibration amplitude decreases.

Design experiment: Fill a glass with unequal amounts of water and tap it with chopsticks to compare the different sounds.

This phenomenon occurs because sound travels more slowly in the air than light travels through the air.

The conditions are not sufficient, only speed, there is no distance and time, so the formula of v=s t is not valid, that is, there is a problem with this question, my talent is limited, please invite another master.

From the inscription, if an object is placed at P, and the object is not visible from the observation window, indicating that the light on the object is blocked by another object and cannot reach the human eye, then it can be judged that P is on the back of the mirror; If two objects are visible when an object is placed at Q, it means that one is the object itself, and the other is a virtual image formed by the reflection of a plane mirror, then it can be judged that Q is on the front side of the mirror. According to the positions of P and Q, it can be judged that the plane mirror should be placed on the diagonal of the magic box, and then the virtual image of the AB object can be drawn by using the imaging characteristics of the plane mirror.

How many plane mirrors are there in the first question box?

The second course: 1. Using a similar triangle, place a vertical stick of a moderate height (measured with a ruler) at the appropriate position of the flagpole. Take a picture of two with a camera. Wash out the ** and measure the proportions with a ruler. Calculate the height of the flagpole.

2. Climb up to measure.

Air, resonance, vibration, hold, sound is generated by vibration, ultrasonic flaw detection (ultrasound), image.

amplitude, gained energy,

1 Air, Vibration 2 Vibration Press and hold The object needs to vibrate 3 Ultrasonic flaw detection 4 Image Amplitude Timbre.

1。Air, vibration.

2。Vibrate, press the drum surface, vibration stops, stops occurs.

3。Do ultrasound.

4。Amplitude, frequency, obtained.

5。Vibration.

1.Air, vibration.

2.Vibration Hold down the drum face The sound is produced by the vibration of an object.

3.Ultrasonic welder.

4.The image amplitude obtained.

5.Timbre.

Known: t=5s v=340m s

Find: sSolution: s=vt=340m s*5s=1700m

Answer; He was about 1700m away from the place where the lightning was generated

1.(1) Tone, loudness, and timbre all describe the characteristics of sound.

Tone: The level of sound is related to the speed of the vibration of the object, the faster the object vibrates, the higher the pitch emitted; The slower the vibration, the lower the pitch; Frequency determines tone.

Loudness: In physics, the strength of a sound is called loudness. Loudness is what we usually call the volume of sound.

Loudness is related to the amplitude of the emitter and the distance from the emitter. At the same distance, the greater the amplitude, the louder it is. The main ways to increase loudness are:

Reduce the divergence of sound.

Timbre: In physics, the sound produced by different objects has different characteristics called musical quality. It is determined by the object itself, that is:

Timbre is related to the material and structure of the emitter. People are able to distinguish different instruments or distinguish different people based on their timbre.

2) Adjectives:

Tones: High, sharp, harsh, 、......

Loudness: Loud, deafening、......

Timbre: beautiful, pleasant, beautiful 、......

2.Sound & Information: Sound can transmit information. (For example: hearing thunder, it is very likely to rain, B ultrasound to check for organ lesions, knock on the porcelain bowl, to determine whether there are cracks, etc.).

Sound & Energy: Sound energy transmits energy. (e.g. ultrasonic cleaning of precision instruments, ultrasonic stone crushing).

1. I think that the tone is the degree that reflects the sharpness and richness of the voice, and the loudness reflects the size, which can be described with words such as whispering, and the timbre is that everyone's voice sounds different, that is, the timbre is different.

2. Transmitting energy is like it has a certain strength, and transmitting information means that we can hear something from the sound, just like buying a watermelon when you knock it to determine whether the watermelon is ripe.