伏安法测电阻接法选择研究

在物理实验教学中,伏安法测电阻存在内、外接两种方法,通常的判定规则为：当待测电阻远大于电流表内阻时,采用内接法;当待测电阻远小于电压表内阻时,则采用外接法．待测电阻的估值究竟多大才算是远大于电流表内阻,从而采用内接法;究竟多小才算是远小于电压表内阻,从而采用外接法．一直以来,这一问题始终没有得到真正解决,本文提出了一种新的解决方案．     

谈谈旧电池对欧姆表测电阻的影响

在电阻的测量中，用欧姆表测电阻快捷方便，但测量不够精确，特别是由于电池用久后，电池电动势略变小，而内电阻要增大，则对测量电阻的误差影响较大．在教学中，就欧姆表测电阻时，当电池用久了，则电阻的测量值与电阻真实值的关系在课堂上展开了讨论，学生讨论气氛热烈，争论激烈，最后形成两种意见．一种认为R测小于R真，并提出依据。其推导过程如下．     

用图像分析限流和分压接法中滑动变阻器的选取

借助Ux-Rap图像分析得出滑动变阻器的选取原则:控制电路采用限流接法时,要求滑动变阻器的最大阻值与被测电阻的阻值接近,即接近为原则;控制电路采用分压式接法时,滑动变阻器的最大阻值应远小于被测电阻的阻值,故在分压接法中,应选择阻值较小而额定电流较大的滑动变阻器.     

探究桥臂电阻及待测电阻的阻值改变对惠斯通电桥相对不确定度的影响

基于惠斯通电桥原理,进行桥臂电阻及待测电阻的阻值改变对惠斯通电桥相对不确定度的影响的探究,得出了在桥臂比为1:1的情况下,随着桥臂电阻的增大,相对不确定度也会随之变化。测得的待测电阻的相对不确定度与桥臂电阻的变化曲线趋势与待测电阻无关,但不同的待测电阻在相同的桥臂电阻的情况下测得的相对不确定度不同。     

正交试验设计法在物理实验方案选择中的应用

介绍了伏安内接法测电阻、电流补偿法测电阻、电压补偿法测电阻的原理,并说明了什么是正交试验设计法,而且以这三种测电阻方法为例详细介绍了正交试验设计法在大学物理实验方案选择中的应用。     

新视角审视补偿法测电阻电路

从欧姆定律、伏安法的视角审视各种补偿法测电阻电路,实际上各种补偿法测电阻电路都是和伏安法一样按欧姆定律方式设计的。实践表明按从消除伏安法测电阻电路系统误差逐步推演出完全补偿法的测电阻电路,再讲授补偿法的原理的思路设计教学,收到了很好的效果。     

充分利用中学实验室器材测电阻

充分利用中学实验室器材测电阻谢继军（苏州市第六中学２１５００１）测电阻方法很多，精确度也越来越高．中学教材中介绍的测电阻的方法是伏安法．教材之所以介绍这种测电阻的方法，主要是考虑到用伏安法测电阻所需物理知识和学生所掌握的知识是一致的．用伏安法测出的电...     

伏安法测电阻

电阻的测量是近年来高考中的热点，也是高考中的难点．在很多复杂多变的测量电阻的电路设计中，其本质思想都是伏安法测电阻．本文从伏安法测电阻实验原理出发，给出伏安法测电阻实验电路，拓展一些常用的测量电阻的方法．     

伏安法测电阻的延伸与思考

伏安法测电阻的原理是R=I-^U,测量电路的设计是围绕测量电阻R两端的电压U和通过电阻R的电流I来间接测量其电阻R值。一般情况下我们会自然地想到用电压表V来直接测电压,用电流表A来直接测电流。但在实际测量中,若电压表不能用或没有电压表的情况下,如何测电压;在电流表不能用或没有电流表的情况下,如何测电流;要解决好这些问题首先要知道到：     

电阻测量实验中“远大于”条件的探讨

电阻的测量是高中物理教学中重要的电学实验,所涉及的实验方法较多,有伏安法、半偏法、替代法、欧姆表法等.其中伏安法、半偏法测电阻时,为减少系统误差,实验条件明确指出待测电阻的阻值必须满足远远大于某电阻的阻值或某电阻的阻值必须远远大于待测电阻的阻值.那么,到底多少才算得上"远远"呢?本文就来讨论这个问题.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Research on beamforming method for dual-line array with space mismatch between the two line arrays

The performance of port/starboard discrimination of dual-line array will be seriously degraded when the space between the two line arrays of the dual-line array is mismatched. The directivity function of the delay-sum and delay-subtract beamforming is deduced and the port/starboard discrimination of the delay-sum and delay-subtract beamforming is also studied both under the ideal status and the status under which the space between the two line arrays of the dual-line array is mismatched. Analysis results show the delay-subtract beamforming has better performance of port/starboard discrimination. At last, the sea trial results demonstrate the theoretical results.     

Retrieval of ultraviolet skylight radiances and O3 slant column densities from balloon-borne limb spectrometer

With a novel light-weight and absolutely calibrated ultraviolet （UV） spectrometer, UV skylight radiances and O3 slant column densities are measured by balloon-borne limb measurements in Xinjiang area, China. UV skylight radiances measured at the height of 31 km are compared with the results from Modtran in the wavelength range from 290 to 420 nm. O3 slant column densities are derived from radiance spectra in the Huggins bands （320 - 335 nm） using differential optical absorption spectroscopy method. And the parameter exhibits a good correlation with the same value simulated by radiative transfer model （Tracy）. The O3 profile simultaneously measured by an O3 sonde is used as input in Tracy calculations. The O3 sonde is launched on the same balloon.     

Design optimization of highly sensitive LSPR enhanced surface plasmon resonance biosensors with nanoholes

For breaking through the sensitivity limitation of conventional surface plasmon resonance (SPR) biosensors, novel highly sensitive SPR biosensors with Au nanoparticles and nanogratings enhancement have been proposed recently.But in practice, these structures have obvious disadvantages.In this study, a nanohole based sensitivity enhancement SPR biosensor is proposed and the influence of different structural parameters on the performance is investigated by using rigorous coupled wave analysis (RCWA).Electromagnetic field distributions around the nanohole are also given out to directly explain the performance difference for various structural parameters.The results indicate that significant sensitivity increase is associated with localized surface plasmons (LSPs) excitation mediated by nanoholes.Except to outcome the weakness of other LSP based biosensors, larger resonance angle shift, reflectance amplitude, and sharper SPR curves' width are obtained simultaneously under optimized structural parameters.     

Polymer gratings based on photopolymerization for low-order distributed feedback polymer lasers

Novel polymer distributed feedback(DFB)gratings are fabricated based on photopolymerization to reduce lasing threshold of polymer lasers.A photopolymer formulation sensitive to 355-nm ultraviolet(UV)light is proposed for the fabrication of polymer gratings and it can be used to form polymer films by spin-coating process.A very low surface-relief depth ranging from 12.5 to about 1.0 nm has been demonstrated with a refractive-index modulation of about 0.012.The experimental results indicate that such polymer gratings have promising potentials for the fabrication of low-order DFB organic semiconductor lasers.