汉明码是如何发现并纠正单个比特错误的？校验位的个数怎么确定？
How does a Hamming code detect and correct a single-bit error, and how is the number of parity bits determined?
汉明码把校验位放在2的幂次位置（1、2、4、8等），第i个校验位负责所有编号的二进制第i位为1的位置，接收端重新计算各组校验并对照收到的校验位，得到出错位置的二进制编号，称为校正子。n个校验位可以定位2的n次方减1个位置，因此要满足2的n次方大于等于m加n加1，其中m是数据位数，例如m为11时n等于4，构成(15,11)汉明码。校正子为0表示无错，非零值直接指出错误位，翻转即可纠正，这就是它纠正单比特错误的原理。
Hamming codes place parity bits at power-of-two positions (1, 2, 4, 8 and so on), and parity bit i covers all positions whose binary index has bit i set; the receiver recomputes the parity groups and compares them with the received parity bits, and the pattern of mismatches, called the syndrome, gives the binary index of the erroneous bit. With n parity bits, 2^n minus 1 positions can be located, so the requirement is 2^n greater than or equal to m plus n plus 1 for m data bits; for m equal to 11, n equals 4, giving the (15,11) code. A zero syndrome means no error, and a non-zero syndrome directly names the flipped bit, which is then inverted, which is how single-bit errors are corrected.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-11-02
来源 · Source
《通信原理》（樊昌信，国防工业出版社）
A Mathematical Theory of Communication, Shannon (Bell System Technical Journal)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9787563511747（豆瓣书目条目: 通信原理）
#汉明码 #纠错编码 #信息论
柔性直流输电（VSC-HVDC）相比传统直流有什么优势，为什么适合海上风电和弱电网？
What advantages does VSC-HVDC have over conventional HVDC, and why suits offshore wind and weak grids?
传统直流靠换相需强交流支撑，柔性直流用电压源换流器可独立控制有功和无功，能主动建压、黑启动。它因此能连接无源海岛、弱电网和波动的海上风电场。
Conventional DC needs a strong AC system to commutate; VSC-HVDC uses voltage-source converters to control active and reactive power independently, even building voltage and black-starting. So it links passive islands, weak grids and fluctuating offshore wind.
难度 专业 · 适合 小学高段(9-12)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Arrillaga，《高压直流输电》（第2版）
Arrillaga, 'High Voltage Direct Current Transmission' (2nd ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9780852969410 (1998)
#柔性直流 #VSC #海上风电
在 CMOS 集成电路里，为什么静态功耗主要来自漏电流而非开关活动？
In CMOS ICs, why does static power come mainly from leakage rather than switching?
理想 CMOS 在静态时一个网络导通、另一个关断，没有直流通路，开关功耗只在充放电瞬间产生。但随着工艺微缩，亚阈值和栅极漏电流显著增大，使静态漏电流成为待机功耗的主要来源。
In ideal CMOS one network is on and the other off in steady state, so there's no DC path and switching power occurs only during transitions. As processes shrink, subthreshold and gate leakage grow, making standby leakage the dominant static power.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-11-03 · 2 条独立证据
来源 · Source
Streetman & Banerjee，《固态电子器件》（第7版）
Streetman & Banerjee, 'Solid State Electronic Devices' (7th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9787121315657（豆瓣书目条目: 固态电子器件） · 核验依据 2 OPENLIBRARY 标识 /works/OL34943756W：Solid State Electronic
#CMOS #漏电流 #功耗
为什么"异步"电动机的转子转速永远比旋转磁场慢一点？
Why does an induction motor's rotor always run slightly slower than the rotating field?
三相定子绕组产生以同步转速旋转的磁场，转子导条相对磁场运动时感应出电流，电流在磁场中受力产生转矩。如果转子转速追平同步转速，转子与磁场的相对运动为零，感应电流消失、转矩归零，所以转子永远以一定的"滑差"落后，实际转速等于同步转速乘以一减滑差率，滑差率一般在1%到5%。负载越重，需要的转矩越大，滑差也越大。正是这个"跟不上"才让电机能带负载运行，也是"异步"名称的由来。
The three-phase stator windings create a field rotating at synchronous speed; the rotor bars move relative to it and have currents induced, and those currents experience force in the field to produce torque. If the rotor ever matched synchronous speed, relative motion would vanish, induced current would die, and torque would go to zero — so the rotor always lags by a "slip", with actual speed equal to synchronous speed times one minus the slip fraction, typically 1-5%. Heavier load needs more torque, hence more slip. That very "lagging behind" is what lets the motor drive loads, and where the name induction/asynchronous comes from.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-10-03 · 2 条独立证据
来源 · Source
《费曼物理学讲义》第二卷（感应电流）
The Feynman Lectures on Physics, Vol. 2 (induced currents)
独立核验依据 · Independent verification: 核验依据 2 ISBN 978-0-7382-0298-3 (2006 Pearson 版，原始版为1963-65 Addis
#异步电机 #滑差 #感应电流
什么是阻抗匹配，为什么射频传输线不匹配会反射信号？
What is impedance matching and why does a mismatched RF line reflect signals?
当传输线特性阻抗与负载阻抗不相等时，行进的电压波在负载处无法被完全吸收，多余部分会反向反射形成驻波，造成功率损失和信号失真。匹配到相同阻抗可让能量最大传输、反射最小。
When a line's characteristic impedance differs from the load, the traveling wave isn't fully absorbed at the load and the excess reflects back, forming standing waves that waste power and distort signals. Matching minimizes reflection and maximizes transfer.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Nilsson & Riedel，《电路》（第11版）
Nilsson & Riedel, 'Electric Circuits' (11th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 978-0-13-747784-5 (11th ed., Pearson)
#阻抗匹配 #反射 #射频
电磁炉为什么不用火也能把锅烧热？
How can an induction cooktop heat a pan without any flame?
炉面下的线圈通交变电流产生变化磁场，在铁质锅底感应出涡电流，电流因锅底电阻发热，所以热直接在锅里产生，炉面本身并不烫。
Coils under the glass carry alternating current creating a changing magnetic field that induces eddy currents in a ferromagnetic pan; the pan's resistance heats it directly while the surface stays cool.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Nilsson & Riedel，《电路》（第11版）
Nilsson & Riedel, 'Electric Circuits' (11th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 978-0-13-747784-5 (11th ed., Pearson)
#电气 #电磁感应 #涡流
为什么全世界电力系统都选三相交流电，而不是两相或四相？
Why does the whole world standardize on three-phase AC, not two or four phases?
三相制的三个相位相差120度，各相功率的脉动互相抵消，合成瞬时功率恒定，电机输出转矩没有波动，这是单相或两相做不到的。用同样三根导线，在三相对称时零线电流为零，输送的功率可达单相系统的约1.732倍，导线材料利用率最高。三相绕组还能天然产生旋转磁场，让三相异步电动机无需启动装置就能自行启动。相数再多（如六相）对功率品质的提升微乎其微，却要多花导线成本，所以三相是综合最优的选择。
Three phases spaced 120 degrees apart cancel each other's power pulsations, giving constant instantaneous total power and ripple-free motor torque — something single-phase or two-phase cannot achieve. With the same three conductors, and zero neutral current when the system is balanced, you can deliver about 1.732 times the power of single-phase, the best utilization of conductor material. Three-phase windings also naturally produce a rotating magnetic field, so three-phase induction motors start by themselves with no starting hardware. More phases (say six) improve power quality only marginally while requiring extra conductors, which is why three-phase is the optimum compromise.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
邱关源 主编 罗先觉 修订,《电路》第5版,高等教育出版社,2006
Qiu Guanyuan ed., Circuit, 5th ed., Higher Education Press, 2006
#三相电 #功率恒定 #旋转磁场
为什么碳化硅（SiC）和氮化镓（GaN）功率器件能让电动车和快充更高效，硅器件卡在哪？
Why do SiC and GaN power devices make EVs and fast chargers more efficient, and where does silicon fall short?
它们是宽禁带半导体，耐更高电压、温度和开关频率，开关损耗和导通损耗都更低，所以充电器更小、车续航更长。硅器件在高频高压下损耗和发热迅速恶化，逼近极限。
They are wide-bandgap semiconductors tolerating higher voltage, temperature and switching frequency with lower loss, so chargers shrink and EV range grows. Silicon's loss and heat rise fast at high frequency and voltage, nearing its limit.
难度 专业 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
Mohan，《电力电子：变换器、应用与设计》（第3版）
Mohan, 'Power Electronics: Converters, Applications and Design' (3rd ed.)
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL31566418W：Power Electronics Conv
#碳化硅 #氮化镓 #宽禁带
用变频器驱动的电机，为什么轴承会出现电蚀损坏？
Why do motors fed by variable-frequency drives suffer electrical bearing damage?
PWM 逆变器输出的三相电压之和不为零，产生高频共模电压，它通过定子绕组与转子、机壳之间的寄生电容耦合到转轴上形成轴电压。当轴电压超过轴承润滑油膜的击穿强度时发生放电，在滚道和滚珠表面熔出微坑，长期积累成搓板状条纹，伴随振动噪声上升并很快导致轴承失效。抑制措施包括安装导电碳刷或轴接地环旁路电流、采用绝缘或陶瓷球轴承切断回路，以及使用对称屏蔽电缆和共模电抗器降低共模电压与 dV/dt。
A PWM inverter's three output voltages do not sum to zero, producing a high-frequency common-mode voltage that couples through parasitic capacitances between stator winding, rotor and frame to appear as shaft voltage. When it exceeds the dielectric strength of the bearing's lubricant film, a discharge melts micro-craters in raceways and balls, which accumulate into washboard fluting with rising noise and vibration and rapid bearing failure. Countermeasures include conductive brushes or shaft grounding rings to bypass the current, insulated or ceramic-ball bearings to break the loop, and symmetrical shielded cable plus common-mode chokes to cut common-mode voltage and dV/dt.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-11-02
来源 · Source
Busse 等，《Bearing currents and their relationship to PWM drives》，IEEE Transactions on Power Electronics 12(2)（1997）
Busse et al., 'Bearing currents and their relationship to PWM drives', IEEE Transactions on Power Electronics 12(2) (1997)
独立核验依据 · Independent verification: 核验依据 1 CROSSREF 标识 10.1109/63.558735：Bearing currents and their
#轴电流 #共模电压 #轴承电蚀
电容器是什么，它在电路里有什么用？
What is a capacitor and what is it used for in circuits?
电容器由两片导体中间夹绝缘层构成，能快速充放电储存电能。它常用来滤波平滑电压、耦合信号、定时，以及在断电瞬间提供短暂电力。
A capacitor is two conductors separated by insulation that stores charge and releases it quickly; it smooths voltage, couples signals, sets timing, and bridges brief power gaps.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Nilsson & Riedel，《电路》（第11版）
Nilsson & Riedel, 'Electric Circuits' (11th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 978-0-13-747784-5 (11th ed., Pearson)
#电气 #电容器 #储能
卫星通信链路预算中的关键损耗有哪些？为什么雨衰对Ku/Ka频段影响很大？
What are the key losses in a satellite link budget, and why does rain fade matter so much in the Ku/Ka bands?
链路预算把发射功率、天线增益、自由空间损耗、大气吸收、雨衰和接收机灵敏度等叠加起来计算链路余量。自由空间损耗随频率的平方和距离的平方增大，静止轨道卫星距离远，单跳损耗巨大。雨衰源于雨滴对电磁波的吸收和散射，频率越高波长越短，雨滴尺寸越接近波长，衰减越严重，因此Ku/Ka频段大雨时可能损失数dB甚至十几dB。工程上用衰减余量、自适应编码调制和上行功率控制来对抗。
A link budget sums transmit power, antenna gains, free-space loss, atmospheric absorption, rain fade and receiver sensitivity to yield the link margin. Free-space loss rises with the square of both frequency and distance, and geostationary satellites are so far away that one hop loses tens of dB. Rain fade comes from absorption and scattering by raindrops; as frequency rises, drop size approaches the wavelength, so attenuation grows, and in the Ku/Ka bands heavy rain can cost several to over ten dB. Fade margins, adaptive coding and modulation, and uplink power control are used to counter it.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 来源待核验 · Source pending review
来源 · Source
出处备注：此条未指向带版次的可引用著作（通识性内容、机构文件或未展开的英文书名），本库不提供独立书目出处；如需精确引用，需由编辑补全具体篇目与版次。
Clarke 1945（地球静止轨道）；Wertz
Clarke (1945, geostationary orbit); Wertz, Space Mission Analysis
#卫星通信 #链路预算 #雨衰
什么是波分复用（WDM）？它如何成倍提升光纤的传输容量？
What is wavelength division multiplexing (WDM), and how does it multiply the capacity of a single fibre?
WDM把多路不同波长的光信号在发送端通过合波器合成一束光注入同一根光纤传输，接收端再用分波器把各波长分离出来，实现一根光纤同时承载多路信号。由于每路波长互相独立、互不干扰，光纤容量就按波长数成倍增长，再加上每路采用高速调制和相干接收，单纤容量可达几十Tbps。它与时分复用不同，是在光域维度上的复用。
WDM combines multiple signals on different optical wavelengths into one beam at the transmit end via a multiplexer, sends them down the same fibre, and at the receive end a demultiplexer separates the wavelengths again, so a single fibre carries many channels at once. Because the wavelengths are independent and do not interfere, capacity grows in proportion to the number of wavelengths, and with high-speed modulation and coherent detection each channel is very fast, pushing single-fibre capacity to tens of Tbps. Unlike time division multiplexing, it multiplies capacity in the optical domain.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Keiser《光纤通信》；Corning 光纤
Keiser, Optical Fiber Communications; Corning optical fiber
独立核验依据 · Independent verification: 核验依据 1 ISBN 9780071007856 (2000)
#波分复用 #WDM #光纤通信
超高压输电线路为什么把一相做成好几根并排的分裂导线？
Why is one phase of an extra-high-voltage line built as several bundled sub-conductors?
单根导线的表面电场强度随电压升高而增大，一旦超过空气击穿场强就产生电晕，带来功率损耗、无线电与可听噪声以及臭氧腐蚀。把一相拆成二到八根间隔布置的子导线后等效半径大幅增大，表面场强显著降低，于是不必使用不切实际的超粗导线就能抑制电晕。分裂还减小线路电抗、提高输送能力，代价是需要间隔棒与更多金具、铁塔风载增大，并要防范子导线间的次跨距振荡与覆冰舞动。
Surface field strength on a single conductor grows with voltage, and once it exceeds air's breakdown strength corona appears, bringing power loss, radio and audible noise and ozone attack. Splitting a phase into two to eight spaced sub-conductors greatly increases the equivalent radius and lowers the surface gradient, suppressing corona without impractically thick conductors. Bundling also reduces series reactance and raises transmission capacity, at the cost of spacers and extra hardware, larger tower wind loads, and the need to control subspan oscillation and ice galloping between sub-conductors.
难度 进阶 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-10-04 · 2 条独立证据
来源 · Source
Grainger 与 Stevenson，《Power System Analysis》（McGraw-Hill，1994）
Grainger & Stevenson, 'Power System Analysis' (McGraw-Hill, 1994)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9780070612938 (1994) · 核验依据 2 ISBN 9780665590955 (2002)
#分裂导线 #电晕损耗 #表面电场强度
为什么长距离输电要用很高的电压，这和家庭安全用电矛盾吗？
Why use very high voltage for long-distance transmission, and does that conflict with household safety?
输电线上损耗功率与电流的平方成正比，升高电压可在相同功率下大幅降低电流，从而减少发热损失。高压只用在输电线路上，到用户端再用变压器逐级降到安全电压，两者并不矛盾。
Line loss grows with the square of current, so raising voltage cuts current for the same power and reduces heat loss. High voltage is only on the lines; transformers step it down to safe levels before it reaches homes.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-10-04 · 2 条独立证据
来源 · Source
Stevenson & Grainger，《电力系统分析》（第3版）
Stevenson & Grainger, 'Power System Analysis' (3rd ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9780070612938 (1994) · 核验依据 2 ISBN 9780665590955 (2002)
#输电 #高压 #损耗
交流电和直流电有什么不同？
What is the difference between AC and DC?
直流电方向始终不变（如电池），交流电方向和大小周期性来回变化（如家用插座）。交流便于用变压器升压远距离输送，直流适合电子设备和储能。
DC flows one way steadily, like a battery; AC reverses direction periodically, like wall outlets. AC is easy to step up for long transmission, while DC suits electronics and storage.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Nilsson & Riedel，《电路》（第11版）
Nilsson & Riedel, 'Electric Circuits' (11th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 978-0-13-747784-5 (11th ed., Pearson)
#电气 #交流电 #直流电
光纤为什么能把光信号传得很远？全内反射的条件是什么？
Why can optical fibre carry signals over long distances, and what conditions make total internal reflection possible?
光纤由高折射率的纤芯和低折射率的包层组成，光以大于临界角的角度入射到纤芯与包层界面时发生全内反射，光被囚禁在纤芯中沿轴向传播而几乎不进入包层。临界角由两种介质的折射率差决定，所以只要纤芯折射率高于包层且入射角足够大，光就能以极低损耗传输。再加上低损耗材料和光放大器补偿衰减，光纤可实现上百公里的中继距离。
An optical fibre has a high-index core and a lower-index cladding; light striking the core-cladding interface at more than the critical angle undergoes total internal reflection and stays trapped in the core, travelling along the axis with almost no loss into the cladding. The critical angle is set by the refractive-index contrast, so as long as the core index exceeds the cladding's and the incidence angle is large enough, light propagates with very low loss. Combined with low-loss materials and optical amplifiers that compensate attenuation, fibre achieves repeater spans of a hundred kilometres or more.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-10-03
来源 · Source
Serway & Jewett，《科学家与工程师的物理学》（第10版）
Serway & Jewett, 'Physics for Scientists and Engineers' (10th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 978-1-337-55327-8
#光纤 #全内反射 #光通信
大功率异步电动机直接启动时，电流为什么能达到额定值的六七倍？
Why does a large induction motor draw six or seven times rated current on direct-on-line starting?
静止瞬间转子与旋转磁场的相对速度最大，转子感应电动势高、频率等于电源频率，此时等效电路中转子回路以漏抗为主而代表负载的等效电阻很小，整机呈现低阻抗，堵转电流可达额定的五到八倍。这股冲击电流会造成电网电压跌落、干扰邻近设备，同时带来剧烈的转矩冲击和绕组温升。工程上用星-三角启动、自耦变压器降压、晶闸管软启动器或变频器把启动电流限制到两三倍以内，代价是启动转矩按电压平方下降，必须仍然大于负载的启动阻力矩。
At standstill the relative speed between rotor and rotating field is maximal, rotor emf is high and at line frequency, so in the equivalent circuit the rotor branch is dominated by leakage reactance with only a small load-representing resistance, leaving low total impedance and locked-rotor current about five to eight times rated. That inrush sags the supply voltage and disturbs nearby equipment while imposing severe torque shock and winding heating. Star-delta, autotransformer, thyristor soft starters or variable-frequency drives limit starting current to roughly two or three times rated, at the cost of starting torque falling with the square of voltage, which must still exceed the load's breakaway torque.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Fitzgerald、Kingsley、Umans，《Electric Machinery》（第7版）
Fitzgerald, Kingsley & Umans, 'Electric Machinery' (7th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9780070211407 (1992)
#异步电动机 #启动电流 #软启动
半导体二极管为什么只能单向导电？
Why does a semiconductor diode conduct in only one direction?
二极管由一个 p 型和一个 n 型半导体形成的 pn 结组成。正向偏置时耗尽层变薄、载流子能通过；反向偏置时耗尽层变宽、几乎阻断电流，于是呈现单向导电。
A diode is a p-n junction. Forward bias thins the depletion region so carriers pass; reverse bias widens it and blocks current, giving one-way conduction.
难度 进阶 · 适合 小学高段(9-12)
CC BY 4.0 · 已核验 · Verified 2026-11-03 · 2 条独立证据
来源 · Source
Streetman & Banerjee，《固态电子器件》（第7版）
Streetman & Banerjee, 'Solid State Electronic Devices' (7th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9787121315657（豆瓣书目条目: 固态电子器件） · 核验依据 2 OPENLIBRARY 标识 /works/OL34943756W：Solid State Electronic
#二极管 #pn结 #单向
静止轨道（GEO）和低轨（LEO）通信卫星各有什么特点？为什么低轨星座延迟更小？
What are the characteristics of GEO versus LEO communication satellites, and why do LEO constellations have lower latency?
GEO卫星在赤道上空约35786公里，周期与地球自转同步，对地静止，单星覆盖广、终端不用跟踪，但单跳延迟约250毫秒（上行加下行）且链路功率要求高。LEO卫星轨道高度仅几百到两千公里，单跳延迟可降到几十毫秒，信号损耗也小，但单星覆盖小，必须组网并频繁切换卫星来维持连续覆盖，这是Starlink等星座的思路。
GEO satellites sit about 35,786 km above the equator with an orbital period matching Earth's rotation, so they appear fixed, cover a huge area and need no terminal tracking, but one hop has roughly 250 ms latency and needs high link power. LEO satellites orbit at a few hundred to 2,000 km, cutting one-hop latency to tens of milliseconds with far less path loss, yet each satellite covers little ground, so a constellation and frequent handovers are required to maintain continuous coverage, the approach taken by Starlink and similar systems.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 来源待核验 · Source pending review
来源 · Source
出处备注：此条未指向带版次的可引用著作（通识性内容、机构文件或未展开的英文书名），本库不提供独立书目出处；如需精确引用，需由编辑补全具体篇目与版次。
Clarke 1945（地球静止轨道）；Wertz
Clarke (1945, geostationary orbit); Wertz, Space Mission Analysis
#卫星通信 #GEO #LEO
逆变器是怎么把直流电"变"成交流电的？
How does an inverter turn direct current into alternating current?
逆变器用IGBT等功率开关管以每秒几千到几万次的高速开断直流母线，输出一串正负交替的方波脉冲；再用脉宽调制（PWM）让脉冲宽度按正弦规律变化，经滤波后得到平滑的正弦交流电。电压和频率都由开关规律决定，所以逆变器既能驱动变频电机调速，也能把光伏板或电池的直流电送上电网，并自动与电网电压相位同步。
An inverter switches the DC bus through power transistors such as IGBTs at rates from a few to tens of kilohertz, chopping it into alternating positive-negative pulses; pulse-width modulation (PWM) varies the pulse widths sinusoidally, and filters smooth the result into a clean sine wave. Both voltage and frequency are set by the switching pattern, so inverters drive variable-speed motors and also feed solar-panel or battery DC into the grid, locking automatically onto the grid's phase.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
王兆安 刘进军 主编,《电力电子技术》第5版,机械工业出版社,2009
Wang Zhaoan and Liu Jinjun eds., Power Electronics, 5th ed., China Machine Press, 2009
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787111268062（豆瓣书目条目: 电力电子技术）
#逆变器 #PWM #功率电子
在开关电源中，为什么提高开关频率可以减小变压器和电感的体积？
In a switching power supply, why does raising the switching frequency shrink the transformer and inductor?
变压器和电感所需磁芯体积与能量存储成正比，而储能与开关周期相关。频率越高，每个周期时间越短，需要的储能越少，因此可用更小的磁芯和更少的匝数实现同样功率。
Core size scales with the energy it must store, which relates to the switching period. Higher frequency means a shorter period and less stored energy per cycle, so the same power needs a smaller core and fewer turns.
难度 进阶 · 适合 小学低段(6-8)
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
Mohan，《电力电子：变换器、应用与设计》（第3版）
Mohan, 'Power Electronics: Converters, Applications and Design' (3rd ed.)
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL31566418W：Power Electronics Conv
#开关电源 #频率 #磁性元件
什么是运算放大器的虚短和虚断，它们为什么成立？
What are the virtual short and virtual open of an op-amp, and why do they hold?
在深度负反馈下，运放两输入端电压被强制几乎相等，称为虚短；又因为输入级阻抗极高，流入两端的电流近似为零，称为虚断。两者是分析放大电路的基础近似。
Under heavy negative feedback the two inputs are forced to nearly equal voltage (virtual short), and because the input impedance is huge, almost no current flows in (virtual open). These are the key approximations for analyzing amplifier circuits.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Nilsson & Riedel，《电路》（第11版）
Nilsson & Riedel, 'Electric Circuits' (11th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 978-0-13-747784-5 (11th ed., Pearson)
#运放 #负反馈 #虚短
为什么发电站要用几十万伏的高压来输电？
Why do power plants transmit electricity at hundreds of thousands of volts?
输电损耗主要来自线路电阻发热，其大小与电流的平方成正比。输送功率一定时，电压升得越高电流就越小，损耗按平方关系急剧下降。所以发电厂把电压升到220千伏、500千伏甚至1000千伏特高压再送出去，长途输送效率可超过90%。但电压太高绝缘成本和电晕损耗又会上升，因此输电距离越长，才越值得用更高电压；超长跨海线路还会改用高压直流进一步降损。
Transmission losses are mostly resistive heating, which grows with the square of the current. For fixed power, raising the voltage cuts the current, and losses drop with the square of it. That is why plants step up to 220 kV, 500 kV, or even 1000 kV ultra-high voltage before sending power out, achieving over 90% efficiency over long distances. But higher voltage means more insulation cost and corona loss, so only longer lines justify it; ultra-long undersea links now switch to high-voltage DC to cut losses further.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-10-04 · 2 条独立证据
来源 · Source
Stevenson & Grainger，《电力系统分析》（第3版）
Stevenson & Grainger, 'Power System Analysis' (3rd ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9780070612938 (1994) · 核验依据 2 ISBN 9780665590955 (2002)
#高压输电 #线路损耗 #特高压
5G毫米波频段有什么优点和缺点？为什么它主要用于热点覆盖？
What are the advantages and disadvantages of the 5G millimetre-wave bands, and why are they mainly used for hotspot coverage?
毫米波（如24至39GHz）频带极宽，可提供数十GHz的可用带宽，因而单载波速率远超中低频段，这是其最大优势。但毫米波波长短，绕射能力弱，穿透墙体、树叶的损耗大，传播距离短，甚至人体遮挡都会造成信号明显衰落。因此毫米波主要用于人流密集的体育场、车站等热点区域做容量增强，而广覆盖仍靠中低频段。
Millimetre-wave bands (e.g. 24 to 39 GHz) offer extremely wide spectrum, giving many tens of GHz of usable bandwidth and per-user rates far beyond sub-6 GHz, their biggest advantage. But the short wavelength diffracts poorly, suffers heavy penetration loss through walls and foliage, has short range, and even a human body in the path causes deep fading. That is why mmWave is mainly deployed in dense hotspots such as stadiums and stations for capacity boost, while wide-area coverage relies on lower bands.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
Rappaport《无线通信》；3GPP 5G 标准；Proakis《数字通信》
Rappaport, Wireless Communications; 3GPP 5G standards; Proakis, Digital Communications
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL2462469W：Wireless communications
#5G #毫米波 #移动通信
Qi标准无线充电的基本原理是什么？为什么要求接收线圈对准发射线圈？
What is the basic principle of Qi-standard wireless charging, and why must the receiver coil align with the transmitter coil?
Qi充电基于电磁感应：发射线圈通入交流电产生交变磁场，接收线圈通过磁耦合感应出电动势，整流后给电池充电。耦合系数随两线圈的对准程度和距离急剧变化，偏离中心时磁通耦合面积减小、效率大幅下降，所以要求线圈对准；Qi还通过异物检测和通信协议协商功率，防止金属异物被磁场加热并保证充电安全。
Qi charging is based on electromagnetic induction: an AC current in the transmitter coil creates an alternating magnetic field, which induces an EMF in the receiver coil that is rectified to charge the battery. The coupling coefficient changes sharply with alignment and gap; off-centre coils reduce the linked flux and drag efficiency down, so alignment matters. Qi also performs foreign-object detection and uses a communication protocol to negotiate power, preventing metal objects from heating up and ensuring safe charging.
难度 进阶 · 适合 大众
CC BY 4.0 · 来源待核验 · Source pending review
来源 · Source
出处备注：此条未指向带版次的可引用著作（通识性内容、机构文件或未展开的英文书名），本库不提供独立书目出处；如需精确引用，需由编辑补全具体篇目与版次。
无线充电联盟（WPC，Qi标准）
WPC (Wireless Power Consortium, Qi Standard)
#无线充电 #Qi标准 #电磁感应
正交幅度调制（QAM）是如何用同一个载波同时传递更多比特的？
How does quadrature amplitude modulation (QAM) carry more bits per symbol on the same carrier?
QAM把载波分解成相互正交的两路，即同相分量（I）和正交分量（Q），每路独立调幅，合成后的每个符号点就同时携带两路信息。比如16QAM有16个符号点，每个符号代表4比特；64QAM有64个点，每符号6比特，频谱效率随调制阶数对数增长。但星座点越密，点间距越小，对噪声和相位噪声越敏感，所以高阶QAM需要更高的信噪比，通常与信道编码和均衡配合使用。
QAM splits the carrier into two orthogonal components, the in-phase (I) and quadrature (Q) axes, each independently amplitude-modulated, so the combined symbol point carries two independent streams at once. 16QAM has 16 constellation points, giving 4 bits per symbol; 64QAM has 64 points or 6 bits per symbol, so spectral efficiency grows logarithmically with modulation order. But denser constellations mean smaller point spacing and higher sensitivity to noise and phase noise, so high-order QAM demands high SNR and is paired with channel coding and equalisation.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-02
来源 · Source
《通信原理》（樊昌信，国防工业出版社）
A Mathematical Theory of Communication, Shannon (Bell System Technical Journal)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9787563511747（豆瓣书目条目: 通信原理）
#QAM #调制 #频谱效率
无线充电为什么不用电线也能把电送进手机，它靠的是哪种物理现象？
How can wireless charging power a phone without wires—what physical phenomenon does it use?
它利用电磁感应：充电板里的交流电产生交变磁场，手机线圈感应出电流再整流成直流电。谐振耦合还能拉近一点距离仍高效，所以手机放上去就悄悄充上了。
It uses electromagnetic induction: AC in the pad makes an alternating magnetic field, and the phone coil induces current that is rectified to DC. Resonant coupling stays efficient a bit farther, so the phone charges quietly when placed on top.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-02
来源 · Source
Kurs 等，《基于强耦合磁共振的无线能量传输》，《科学》317卷，83–86页（2007）
Kurs et al., 'Wireless Power Transfer via Strongly Coupled Magnetic Resonances,' Science 317, 83–86 (2007)
独立核验依据 · Independent verification: 核验依据 1 EUROPEPMC 标识 17556549：Wireless power transfer via strong
#无线充电 #电磁感应 #谐振
变压器是怎样改变电压的？
How does a transformer change voltage?
变压器用两组匝数不同的线圈和铁芯，交流电在一组产生变化磁场，在另一组感应出电压；匝数多的输出高压、匝数少的输出低压。
It uses two coils of different turns on an iron core; the alternating current in one coil makes a changing magnetic field that induces a different voltage in the other, set by the turn ratio.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-10-04 · 2 条独立证据
来源 · Source
Stevenson & Grainger，《电力系统分析》（第3版）
Stevenson & Grainger, 'Power System Analysis' (3rd ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9780070612938 (1994) · 核验依据 2 ISBN 9780665590955 (2002)
#电气 #变压器 #电压
为什么锂电池可以反复充电，而普通干电池用完了就只能扔？
Why can a lithium battery be recharged hundreds of times while a primary dry cell cannot?
锂离子电池是二次电池：放电时锂离子从石墨负极脱出、穿过电解液嵌入正极金属氧化物，充电时外加电压让锂离子反向迁回负极，这是可逆的嵌入-脱出反应，因此能循环上千次。而碱性干电池的放电反应不可逆，正极活性物质一旦消耗就没了。锂电池能量密度高靠的是锂原子轻、电压高，但其寿命仍受容量衰减和析锂等问题的限制。
A lithium-ion cell is a rechargeable battery: on discharge, lithium ions leave the graphite anode, cross the electrolyte, and insert into a metal-oxide cathode; charging forces them back in reverse. This reversible intercalation-deintercalation allows thousands of cycles. An alkaline dry cell's chemistry is irreversible — once the cathode material is consumed it is gone. Lithium cells pack more energy because lithium is light and the cell voltage is high, though cycle life is still capped by capacity fade and lithium plating.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Linden & Reddy，《林登电池手册》（第4版）
Linden & Reddy, 'Lindens Handbook of Batteries' (4th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 978-0-07-037921-3 (1995, McGraw-Hill)
#锂电池 #可逆反应 #能量密度
为什么电动机通上电就会转起来？
Why does an electric motor spin when current flows?
电动机靠磁场相互作用转动：定子线圈通电产生旋转磁场，转子（永磁体或感应电流）处在这个磁场中，载流导体受到的电磁力让转子追逐旋转磁场，感应电机的转速略低于同步转速，同步电机则与之完全同步。直流电机靠换向器在转子转到合适角度时切换电枢电流方向，使转矩始终朝同一方向，转子才能持续旋转；交流异步电机则靠转子与旋转磁场之间的速度差（滑差）维持感应电流，同步电机靠转子磁极锁定旋转磁场。输出力矩的大小由电流与磁场强度的乘积决定。
A motor spins through interacting magnetic fields: current in the stator windings creates a rotating field, and the rotor (permanent magnets or induced currents) sits inside it and feels electromagnetic force on its conductors, which makes the rotor chase the rotating field — an induction rotor runs slightly below synchronous speed, while a synchronous rotor locks to it exactly. In a DC motor the commutator switches the armature current direction as the rotor reaches the right angular position, so torque keeps acting in one rotational direction and the rotor keeps spinning; an induction motor relies on the speed difference (slip) between rotor and field to sustain the induced currents, while a synchronous motor locks its poles to the rotating field. Output torque is set by the product of current and field strength.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Fitzgerald 等《电机学》(Electric Machinery)；Tesla《多相交流电机》(1888)
Fitzgerald et al., 'Electric Machinery'; Tesla, 'A New System of Alternating Current Motors' (1888)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9780070211407 (1992)
#电动机 #旋转磁场 #电磁力
发电机是怎样把运动变成电的？
How does a generator turn motion into electricity?
让线圈在磁场中转动（或让磁场相对线圈动），磁通量变化就会在线圈里感应出电流，这就是法拉第电磁感应，水轮、风轮都是先转再发电。
Rotating a coil in a magnetic field changes the magnetic flux and induces a current by Faraday's law; water and wind turbines spin first, then generate.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Nilsson & Riedel，《电路》（第11版）
Nilsson & Riedel, 'Electric Circuits' (11th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 978-0-13-747784-5 (11th ed., Pearson)
#电气 #发电机 #电磁感应
电池里的电是怎么存起来的？
How is electricity stored inside a battery?
电池里有两种不同的材料泡在电解液里，化学反应会把电子推到一侧积存起来。用电器接通时，电子从一边流向另一边形成电流，反应慢慢消耗完电就没了。
A battery has two different materials in an electrolyte; chemical reactions pile electrons on one side. When you connect a device, electrons flow from one side to the other as current, and the reaction runs down until empty.
难度 入门 · 适合 幼儿(3-6)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Linden & Reddy，《林登电池手册》（第4版）
Linden & Reddy, 'Lindens Handbook of Batteries' (4th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 978-0-07-037921-3 (1995, McGraw-Hill)
#电池 #化学 #电子
为什么手机充电器要把交流电变成直流电？
Why does a phone charger convert AC to DC?
电网送来的是方向和大小周期性变化的交流电，而手机电池和内部电路需要方向恒定的直流电才能稳定充放电。充电器里的整流电路先把交流变直流，再降压到合适的电压。
The grid supplies alternating current that reverses direction, but a phone battery and its circuits need steady direct current. The charger rectifies AC to DC, then steps it down to the right voltage.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Nilsson & Riedel，《电路》（第11版）
Nilsson & Riedel, 'Electric Circuits' (11th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 978-0-13-747784-5 (11th ed., Pearson)
#充电器 #交流电 #直流电
电池是怎样储存和放出电能的？
How does a battery store and release electrical energy?
电池内部发生化学反应，把化学能存起来；接通电路时反应反向进行，电子从一端流到另一端形成电流，电就用掉了。
A battery stores energy in chemical reactions; when connected, the reaction runs the other way and electrons flow from one terminal to the other as current, delivering power.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Linden & Reddy，《林登电池手册》（第4版）
Linden & Reddy, 'Lindens Handbook of Batteries' (4th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 978-0-07-037921-3 (1995, McGraw-Hill)
#电气 #电池 #化学能
避雷针是怎样保护建筑物的？
How does a lightning rod protect a building?
金属避雷针立在最高处，通过粗导线把雷电引到地下，让巨大电流安全地导入大地，而不是击穿房顶或引发火灾。
A metal rod at the highest point channels lightning through a thick wire into the ground, safely dumping the huge current into Earth instead of through the roof.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Nilsson & Riedel，《电路》（第11版）
Nilsson & Riedel, 'Electric Circuits' (11th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 978-0-13-747784-5 (11th ed., Pearson)
#电气 #避雷针 #防雷