some introductions of physics II lab Essay

Submitted By YuntingZhang
Words: 5372
Pages: 22

Introduction: Today, we will measure the speed of sound in air by equation v = f λ, where v is speed of sound, f is frequency and λ is wavelength. Sound is a kind of wave and it propagates through medium. Frequency is how often a wave peak goes by and wavelength is the distance from the high point of one wave to the next one. In musicians frequency determines the pitch of the sound: the quicker frequency is, the higher pitch is. The maximum distance the sound wave moves above or below the equilibrium value is called the amplitude, A. Amplitude determines the loudness of the sound: the larger amplitude is, the louder sound is. We will use a column of air and a tuning fork to measure wavelength λ. When a wave goes through a column of air, it would appear node and anti-node. Node is minimal amplitude which is zero and the column of air has node at the end of the tube. The opposite node named anti-note, it's a point where the maximal amplitude is, it always occurs at midway between two nodes. In other words to explain node and anti-node, the node is the point which is the incoming wave and reflected wave meet together, and anti-node is the point which the distance between the incoming wave and the reflected wave is maximum. Resonance is two objects vibrate at the same natural frequency and objects always occur resonance when wave is at anti-node. Standard wave is vibrating up and down in place, which is the sum of the incoming wave and the reflected wave. We will reduce water from the column of air, and vibrate a tuning fork above it at the same time, when the sound from the column of air becomes the largest one (it means the tuning fork and the column of air have the same natural frequency or resonance is happening), we will know this distance, L, from the top to the bottom of column is 1/4 wavelength, because of the point is the first anti-node. L1 = 1/4λ. Then we continue reduce water from the column of air and vibrate a tuning fork above it at the same time. We will observe another largest sound during this time, it is the second anti-node and 3/4λ. L2 = 3/4λ. We can guess if we still continue reduce water from the column (if the column of air is enough long), we will meet the third anti-node, which is 5/4λ; the forth anti-node, which is 7/4λ; and so on. Therefore, the odd number of multiples of 1/4 wavelength will produce resonance. In order to reduce the error of experiment we can use this equation: λ = 2(L1 - L2) to calculate wavelength. Speed of sound depends on elasticity, density of medium and temperature. The larger elasticity is the quicker the speed of sound has. The larger density is, the quicker the speed of sound has. The higher temperature is, the quicker the speed of sound has. When sound traveling through air, the relationship between the speed of sound and temperature is v = (331.4m/s) )^-2 (where the T is Kelvin) or v = 331.4m/s + 0.60m/s T (where the T is Celsius degree). The relationship between Celsius and Kelvin degree is T oC = T K - 273 K.
Today, our purpose is to study the electrostatic charges re-arrange themselves by using a hard rubber stick and a wool cloth, and a glass rod and silk or saran wrap. We will rub them and use an electroscope to test and verify them change electrostatic charges. There are two types of charges in nature: positive and negative. The like charges repel and opposite charges attract. Science provisions, if the electric is the same as the electric after glass rod rubbed with silk, called positive charge; if the electric is same as the electric after fur rubbed with rubber stick, called negative charge. The unit of charge is Coulomb (C). In an isolated system, charge is always conserved, as the conservation of mass and the conservation of energy. Therefore, in the universe, the creation and destroy of charges always in pairs with equal and opposite. They would create or destroy at the same time. An atom is made up by three…