Determination of Electronic Charge in College Physics

Answer 1

There were many ways to measure the charge of an electron:
1. ** Millikan's Oil Drop Experiment **
- Principle: When charged ions pass through the cloud chamber, they will condense into small water droplets. First, measure the charge-to-mass ratio of the small water droplets, then measure the mass of the water droplets to calculate the charge carried by the ions, and then obtain the electron charge value. However, the water droplet was too small to measure its mass directly. The mass could be calculated by measuring the falling speed of the water droplet under the effect of gravity. The water droplets accelerated under the effect of gravity. As the speed increased, the air's viscous resistance increased. When the water droplets offset gravity, they fell at a constant speed. According to Newton's second law,[G = MG]([G] is gravity,[m] is mass,[g]= 9.8m/s2]), and Stokes 'viscous resistance formula [F = 6 pi eta rv]([F] is viscous resistance,[eta] is air viscous coefficient,[r] is the radius of the water droplet, and [v] is the speed), when the water droplet falls at a constant speed, there is [MG=6 pi eta rv]. From this, the relationship between the mass and the radius of the water droplet can be obtained. And because the mass of the water droplet is m={frac{4}{3} pi r ^{p}}({p} is the density of water), the average mass of the water droplet in the cloud chamber can be calculated. Finally, sulfuric acid was used to absorb all the water droplets and the charges in them. Since the charge and mass of each water droplet were the same, the charge-to-mass ratio of each water droplet was obtained through the final charge-to-mass ratio of sulfuric acid.
2. ** Using a voltage meter and a voltage meter to measure **
- Principle: By charging a transformer, then measuring the voltage at both ends of the transformer, the amount of electron charge can be calculated according to the relevant formula. During the measurement process, attention should be paid to eliminating interference from electromagnetic radiation, temperature changes, and other factors.
- [Operation process: Prepare the experiment equipment such as a transformer, a voltage meter, a wire, and a power supply.] Charging the voltage to the required voltage, calculating the number of electronic charges according to the voltage value and the capacity of the voltage, connecting the voltage meter to the voltage meter and ensuring the connection is stable, recording the voltage value at both ends of the voltage meter, and analyzing the experimental data to draw a conclusion.
3. ** Modern version of the experiment (Method of the scientists at Gothenburg University)**
- Principle: Use a laser to trap a water droplet in a strong electric field, and then add a single electron by exposing it to alpha radiation. Each time the water droplet absorbs one or more electrons, it will undergo a quantitative jump. Through a single lens to magnify the image of the droplet, observe the effect of the single electron absorption and measure the jump magnitude with a ruler. According to the relationship between the jump magnitude and the increase of electrons, the relevant conclusion of the electron charge can be obtained.
- Operation: A 29-micrometer-sized droplet of silicon oil was thrown into a laser beam formed by a green laser with a 532-nanometer-length directed upward and focused by a lens with a focal length of 100 mm.(The focal point is between two poles separated by 1 mm and applied with a potential difference of 666V), so that the droplet is captured. Alpha radiation is directed to the almost uncharged droplet to vaporize the surrounding air. When the droplet gains or loses charge, the electric field force changes and thus changes its position. These effects are magnified by 73 times and projected on the wall. The millimeter ruler is placed on the wall to observe the number of electrons obtained by the droplet (each additional electron jumps about 1 mm).
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