普朗克常量的测定

普朗克常量的测定 实验 普朗克常量的测定 实验人: 学号: 实验时间: 实验概述 【实验目的及要求】 1(通过实验深刻理解爱因斯坦的光电子理论，了解光电效应的基本规律; 2(掌握用光电管进行光电效应研究的方法; 3(学习对光电管伏安特性曲线的处理方法，并用以测定普朗克常数。 【仪器及用具】 高压汞灯、滤色片、光电管、微电流放大器(含电源) 【实验原理】 爱因斯坦从他提出的“光量子”概念出发，认为光并不是以连续分布的形式把能量传播到空间，而 h,是以光量子的形式一份一份地向外辐射。对于频率为的光波，每个光子的能量为，其中，h,6.6261, -34×10焦耳?秒，称为普朗克常数。 当频率为的光照射金属时，具有能量 h的一个光子和金属中的一个电子碰撞，光子把全部能量,, 传递给电子。电子获得的能量一部分用来克服金属面对它的束缚，剩余的能量就成为逸出金属表面后光电子的动能。显然，根据能量守恒有: E,h,,W (1) ks 这个方程称为爱因斯坦方程。这里,为逸出功，是金属材料的固有属性。对于给定的金属材料，,是ss一定值。 爱因斯坦方程表明:光电子的初动能与入射光频率之间呈线性关系。入射光的强度增加时，光子数 h,W目也增加。这说明光强只影响光电子所形成的光电流的大小。当光子能量,时，不能产生光电子。S ,,,W/h即存在一个产生光电流的截止频率()。 00S 本实验采用的实验原理图见图1。一束频率为的单色光照射在, 真空光电管的阴极,上，光电子将从阴极逸出。在阴极,和阳极,K A 之间外加一个反向电压V(A接负极)，它对光电子运动起减速作KA 用。随着反向电压V的增大，到达阳极的光电子相应减少，光电流KAG 减少。当V,,时，光电流降为零。此时光电子的初动能全部用KASV 于克服反向电场作用。即 Ee,, (2) Sk 这时的反向电压,叫截止电压。入射光频率不同时，截止电压也不S 同。将(2)式代入(1)式得 图1 Million. Water quality standards the dredging of river boundary section obtained provincial environmental protection Office special bonuses for wetland construction ... ... Million. But sober see, these achievements were made in the case of decreased rainfall for two consecutive years, we realize that environmental protection work still faced many problems in our County. Mainly in the PM2.5 and PM10 air quality monitoring indicators often exceeding, dredging of river section's water quality is not stable, and rural non-point source pollution has not been radical, Wade through the corporate environmental risk, livestock pollution rebound from severe, a wealth of protection and use of water resources is not well. If this year's rainfall, these problems will be exposed, and raw materials caused a great deal of pressure to go green. To solve these problems, we focused on three aspects of the work of environmental protection: (a) in accordance with the ... ... Real good green. According to the "Garden City, roads, tree-lined, mountain forests of" principle, to develop "governance focused piece, scale" afforestation programmes, and actively implement the barren hills green, River afforestation increased, City Green, farmland and other greening works to ensure complete afforestation this year ... ... Acres and acres and afforestation in the plain ... ... Acres, new nursery wood ... ... MU. h (3) U,(,,,)s0e 式中h，e都是常量，对同一光电管也是常量，实验中测量不同频率下的U，做出U—v曲线。在(3),ss0 式得到满足的条件下，这是一条直线。若电子电量e为已知，由斜率k=h/e可以求出普朗克常数h，由直线在U轴上的截距可以求出逸出功W，由直线在v轴上的截距可以求出截止频率v，见图2。 ss0 I Us Is U sν 0W/e ν s1 2 图3 光电管伏安特性曲线 图2 U—v曲线 s 在实验中测得的伏安特性曲线与理想的有所不同，这是因为: 1.光电管的阴极采用逸出电位低的碱金属材料制成，这种材料即使在高真空也有易氧化的趋向，使阴极表面各处的逸出电势不尽相等。同时逸出具有最大动能的光电子数目大为减少。随着反向电压的增高，光电流不是陡然截止，而是较快降低后平缓地趋近零点。 2.阳极是用逸出电势较高的铂、钨等材料做成。本来只有远紫外线照射才能逸出光电子。但在使用过程中常会沉积上阴极材料，当阳极受到部分漫反射光照射时也会发生光电子。因为施加在光电管上的外电场对于这些光电子来说正好是个加速电场，使得发射的光电子由阳极飞向阴极，构成反向电流。 3.暗盒中的光电管即使没有光照射，在外加电压下也会有微弱电流流通，称作暗电流。其主要原因是极间绝缘电阻漏电(包括管座以及玻璃壳内外表面的漏电)阴极在常温下的热电子辐射等。暗电流与外加电压基本上成线性关系。 由于以上原因，实测曲线上每一点的电流是阴极光电子发射电流、阳极反向光电子电流及暗电流三者之和。理想光电管的伏安特性曲线如图3的虚线所示，实际测量曲线如图中的实线表示。 光电效应实验仪原理见图4。常见的GDh-1型光电管阴极为Ag-,-K化合物，最高灵敏度波长为410?10nm。为避免杂散光和外界电磁场的影响，光电管装在留有窗口的暗盒内。 实验光源为高压汞灯，与滤色片配合使用，可以提供356.6，404.7，435.8，546.1，577.0nm五种波长的单色光。 由于光电流强度非常微弱，一般需要经过微电流放大器放大后才能读出。微电流放大器的测量范围-8-1310~10A，共分六档。光电管的极间电压由直流电源提供，电源可以从负到正在一定范围调节。 实验时可以由电压表和电流表逐点读数，并根据测量数据做图。也可以由锯齿波发生器产生随时间 X 微电流放大器 V 锯齿波直流电 A Y 源 发生器 , ? 图4: 光电效应实验原理图 连续增大的电压加在光电管上，这时光电流也是连续变化的。将电流、电压量分别接在X-Y记录仪的Y 端和X输入端(或计算机A/D转换器的输入端)，就能自动画出光电管的伏安特性曲线。 Million. Water quality standards the dredging of river boundary section obtained provincial environmental protection Office special bonuses for wetland construction ... ... Million. But sober see, these achievements were made in the case of decreased rainfall for two consecutive years, we realize that environmental protection work still faced many problems in our County. Mainly in the PM2.5 and PM10 air quality monitoring indicators often exceeding, dredging of river section's water quality is not stable, and rural non-point source pollution has not been radical, Wade through the corporate environmental risk, livestock pollution rebound from severe, a wealth of protection and use of water resources is not well. If this year's rainfall, these problems will be exposed, and raw materials caused a great deal of pressure to go green. To solve these problems, we focused on three aspects of the work of environmental protection: (a) in accordance with the ... ... Real good green. According to the "Garden City, roads, tree-lined, mountain forests of" principle, to develop "governance focused piece, scale" afforestation programmes, and actively implement the barren hills green, River afforestation increased, City Green, farmland and other greening works to ensure complete afforestation this year ... ... Acres and acres and afforestation in the plain ... ... Acres, new nursery wood ... ... MU. 由于暗电流和阳极电流的存在，准确地测量截止电压是困难的。一般采用下述两种方法进行近似处理: 1( 若在截止电压点附近阴极电流上升很快，则实测曲线与横轴的交点(图3中的“1”点)非常接近于U点。以此点代替U点，就是“交点法”。 ss 2( 若测量的反向电流饱和很快，则反向电流由斜率很小的斜线开始偏离线性的“抬头点”(图3中的“2”点)电压值与U点电压非常接近，可以用“抬头点”电压值代替U点电压。 ss 实验内容 【实验设计】(测量及调节方法) 1. 按要求布置好仪器，打开微电流放大器的电源预20分钟。 2. 罩好暗盒窗上的遮光罩，测量暗电流随电压的变化。 3. 选择好某一波长的入射光，由,2V开始增加电压进行粗测。注意观察电流变化较大时对应的电压区间，细测时在此区间应内多取一些测量点，以减小描绘曲线时的误差。 4. 在以上基础上精确测量I随U变化的数据。 5. 更换滤色片，选择其它波长，重复第2项和第3项实验内容。 6. 做各波长I-U曲线，用“抬头点”确定U点。 s 7. 做U—ν曲线，验证爱因斯坦公式。用作图法或最小二乘法求斜率并外推直线求截距，计算普朗s 克常数h、逸出功W和截止频率ν。 s0 8. 用锯齿波发生器做电源，由X-Y记录仪(或计算机)绘图，进行第5项和第6项工作。 9. 用移动光源位置或改变窗口大小的方法改变入射光的强度，观测W、ν和饱和电流I的变化。 s0s 实验中要注意如下事项: 1. 汞灯打开后，直至实验全部完成后再关闭。一旦中途关闭电源，至少等5分钟后再启动。 2. 注意勿使电源输出端与地短路，以免烧毁电源。 3. 实验过程中不要改变光源与光电管之间的距离(第,项内容除外)，以免改变入射光的强度。 4. 注意保持滤色片的清洁，但不要随意擦拭滤色片。 5. 实验后用遮光罩罩住光电管暗盒，以保护光电管。 【数据表格】(画出数据表格，写明物理量和单位) Million. Water quality standards the dredging of river boundary section obtained provincial environmental protection Office special bonuses for wetland construction ... ... Million. But sober see, these achievements were made in the case of decreased rainfall for two consecutive years, we realize that environmental protection work still faced many problems in our County. Mainly in the PM2.5 and PM10 air quality monitoring indicators often exceeding, dredging of river section's water quality is not stable, and rural non-point source pollution has not been radical, Wade through the corporate environmental risk, livestock pollution rebound from severe, a wealth of protection and use of water resources is not well. If this year's rainfall, these problems will be exposed, and raw materials caused a great deal of pressure to go green. To solve these problems, we focused on three aspects of the work of environmental protection: (a) in accordance with the ... ... Real good green. According to the "Garden City, roads, tree-lined, mountain forests of" principle, to develop "governance focused piece, scale" afforestation programmes, and actively implement the barren hills green, River afforestation increased, City Green, farmland and other greening works to ensure complete afforestation this year ... ... Acres and acres and afforestation in the plain ... ... Acres, new nursery wood ... ... MU. 【数据处理及结果】 Million. Water quality standards the dredging of river boundary section obtained provincial environmental protection Office special bonuses for wetland construction ... ... Million. But sober see, these achievements were made in the case of decreased rainfall for two consecutive years, we realize that environmental protection work still faced many problems in our County. Mainly in the PM2.5 and PM10 air quality monitoring indicators often exceeding, dredging of river section's water quality is not stable, and rural non-point source pollution has not been radical, Wade through the corporate environmental risk, livestock pollution rebound from severe, a wealth of protection and use of water resources is not well. If this year's rainfall, these problems will be exposed, and raw materials caused a great deal of pressure to go green. To solve these problems, we focused on three aspects of the work of environmental protection: (a) in accordance with the ... ... Real good green. According to the "Garden City, roads, tree-lined, mountain forests of" principle, to develop "governance focused piece, scale" afforestation programmes, and actively implement the barren hills green, River afforestation increased, City Green, farmland and other greening works to ensure complete afforestation this year ... ... Acres and acres and afforestation in the plain ... ... Acres, new nursery wood ... ... MU. 【讨论】 指导教师评语及成绩 【评语】 成绩: 指导教师签名: 批阅日期: Million. Water quality standards the dredging of river boundary section obtained provincial environmental protection Office special bonuses for wetland construction ... ... Million. But sober see, these achievements were made in the case of decreased rainfall for two consecutive years, we realize that environmental protection work still faced many problems in our County. Mainly in the PM2.5 and PM10 air quality monitoring indicators often exceeding, dredging of river section's water quality is not stable, and rural non-point source pollution has not been radical, Wade through the corporate environmental risk, livestock pollution rebound from severe, a wealth of protection and use of water resources is not well. If this year's rainfall, these problems will be exposed, and raw materials caused a great deal of pressure to go green. To solve these problems, we focused on three aspects of the work of environmental protection: (a) in accordance with the ... ... Real good green. According to the "Garden City, roads, tree-lined, mountain forests of" principle, to develop "governance focused piece, scale" afforestation programmes, and actively implement the barren hills green, River afforestation increased, City Green, farmland and other greening works to ensure complete afforestation this year ... ... Acres and acres and afforestation in the plain ... ... Acres, new nursery wood ... ... MU.