留学资讯 一手掌握

美国大学的物理是一门非常难的课程，它涉及到很多知识点，不仅仅对数学的计算能力要求非常高，而且还要用清晰的逻辑思维。留学府根据调查显示，每年外出留学的学子们选择物力专业的人也是不少的，他们都有一股挑战性，有丰富的动手能力。当然，物理这一课程也不是那么容易学的，也有很多留学生因为专业知识的不懂，导致每次物理考试的时候都得不到高分。洋蜜蜂也提供物理专业tutor来帮助大家学习这门课程，下面就是物理课程在线辅导，希望对大家有所帮助。

Lab 1. Electrical Force

Data and time 

1.Introduction 

This lab was to compute the fundamental constant of nature with the help of the electrical force balance. Two parallel plates are the important part of the delicate balance system. The mass which placed on the top plate, the distance between those two places was changed. With the help of the mirror and laser, the changed distance can be measured. Using the format which connects with the balance relationship between the electrical force and the gravitational force, the fundamental constant of nature  can be calculated.

1.Theory

The vacuum dielectric constant .

The basic structure of the two parallel plates can be seen in Fig. 1. The area of each flat plate is A and the separate distance is y. Q is the positive charge placed on the top of the plate and -Q is the second charge placed on the second plate. 

Figure 1. Two parallel plates with the area A and separate distance y.

When just place charge Q on the top of the plate, add a mass m on the top of the plate, because of the gravitational force, the separation distance between the two plate is changed. The gravitational force is  

G=mg   (1)

The magnitude of the electric field can be approximately calculated by

(2)

Then add the second charge -Q on the second plate. The magnitude of the force between those two plate can be calculated through

(3)

The voltage that apply on the plate can be calculated as

(4)

The charge Q can be write as 

(5)

Plugging Eq. (5) into Eq. (3), the magnitude of the force between those two plate can be calculated with 

(6)

When the voltage creates the same deflection as the mass,  

F=G=mg    (7)

Then the the fundamental constantcan be wrote as

(8)

Using the standard deviation to calculate the uncertainly.

(9)

where n is the number of the sample, is the observed values of the sample,  is the average value.

2.Experiment overview

Step 1. We constructed the measurement system like Fig. 2 and checked all the factors in order to make sure the setup was working. With the help of the laser, mirror and the vertical ruler, the displacement of the two parallel plates can be precisely measured.

Step 2. Chosen a suitable separate distance y estimate between the two plates and recorded it. Measured and recorded the distance X from the center of the plate to the axis of the pivot in order to calculate the area of the plates. 

Figure 2. The basic structure of the measurement system.

Step 3. Then start the lab with turned on the laser. Make sure that the horizontal laser hit the mirror and the laser can be reflected on the ruler. Recorded the position of the laser on the ruler as h0, it should be mentioned that must choose a point of the laser to constant measured because of the width of the laser beam.

Step 4. Added a mass with 500 mg on the top of the plate and recorded the new position of the laser on the ruler as h touch.

Step 5. Moved 500 mg mass and checked the position of the laser on the ruler when the system came to balance. If it does not return to h0, with help of the knurled knob to relocate knife edge and lift the plate. Write down the new equilibrium position. If it returns to h0, continue the experiment. 

Step 6. Measured and recorded the distance between the mirror and the ruler as D. Calculated the displacement of the height and then measured the initial separate distance y0 of the two plates. 

(10)

(11)

Step 7. Placed and recorded the massat the center of the pan and verified the distance between the plates is about half of the original separation. Recorded the height on the meter stick and uncertainty. 

Step 8. Calculated the displacement of the height and then measured the initial separate distance of the two plates with.

(12)

(13)

Step 9. Repeated step 7 with less massand verified the distance between the plates is about 2/3 of the original separation. Calculatedand. Repeated again with less mass and recorded,,.

Step 10. Make sure the voltage to zero then turned on the power source. It is necessary to slowly adjust the voltage until the laser spot on the ruler is reached h1. Recorded the voltage V1. Then did the same work to recorded the voltages V2 and V3.

Step 11. Calculated each  with different voltages, then get the average value and the standard deviation of the.  

3.Data analysis

The results of the experiment measurement and calculation are showed in Tab. 1

Table 1. The results of lab.

According to the results of this lab, the final result of the fundamental constant is

(14)

Compare with the theoretical value , all the values are within the right order of magnitude, but not within the experimental range.

4.Conclusion

The aim of this lab is to calculate the fundamental constant of nature. During this experiment, I have understand the electrical force measure with balance. The results that we measured are not within the experimental range. The error probably came from the artificial reading on the rule. 

以上就是洋蜜蜂给留学生们带来的美国大学物理课程辅导，叙述的是一个实验课程。本实验的目的是计算自然的基本常数，可能存在些许的误差。提供这次的实验也是为了各位留学生们可以更好的学习物理，如需更深沉的物理考前辅导可以联系微信yuff996，可以免费试听30分钟哦。