Question bank — Ion engine — ionization, acceleration grid, neutralizer

False. Ise isliye choose kiya gaya hai kyunki yeh heavy hai (har ion mein bada momentum), ionize karna easy hai (12.13 eV), inert aur storable hai — xenon actually rare aur expensive hai.

False. Electric fields sirf charged objects ko push karti hain; ek neutral atom koi force feel nahi karta, yahi wajah hai ki Stage 1 (ionization) pehle aani chahiye.

False. Thrust momentum $mv$ se aata hai, charge se nahi. Ion electron se ~240,000 guna bhaari hai, isliye woh essentially saara momentum carry karta hai; electrons sirf charge fix karte hain.

False. Kyunki $v_e=\sqrt{2qV/m}$, exhaust speed $\sqrt{V}$ ke saath scale hoti hai, isliye $V$ double karne se $v_e$ sirf $\sqrt{2}\approx 1.41$ se multiply hoti hai.

True. Thrust bahut tiny hai (≈0.1 N, coin-weight) kyunki ion flow rate kam hai — lekin yeh mahino tak chalti hai, huge total $\Delta v$ deti hai. Dekho Chemical vs Electric Propulsion.

True. Agar $I_{neutralizer}=I_{beam}$ hai, toh ions ke roop mein nikalne wala charge electrons ke roop mein nikalne wale charge se match hota hai, isliye spacecraft constant potential par rehti hai.

False. Xenon woh reaction mass hai jo bahar feka jata hai; electricity sirf ise accelerate karti hai. Xenon khatam → koi thrust nahi, chahe full power ho.

False. Thrust current-limited hai is baat se ki kitne ions extract kiye ja sakte hain (Child–Langmuir limit); extra $V$ mainly efficiency (specific impulse) kharidta hai, bada thrust nahi. Dekho Child-Langmuir Space Charge Law.

False. Woh freed electron aur atoms ionize karta rehta hai, discharge ko sustain karta hai — yeh ek self-feeding chain hai, waste nahi.

Error: electrons ka mass negligible hai (~1/240000 of a xenon ion) aur speed bhi kam hai, isliye $\dot{m}{v}_e$ mein unka contribution essentially zero hai.

Error: light ions tezi se jaate hain lekin kam momentum carry karte hain. Thrust $F=I\sqrt{2mV/q}$ actually mass $m$ ke saath badhta hai, heavy ions ko favour karta hai.

Error: sirf magnitude matter karta hai. Ek positive ion positive-to-negative drop se guzarta hai; work $qV$ positive hai kyunki field ion ko sahi direction mein point karti hai.

Error: screen grid high positive hai; woh outer accelerator grid hai jo strongly negative hai, positive ions ko bahar kheenchta hai aur electrons ko wapas aane se rokta hai.

Error: dono same direction mein (peeche ki taraf) nikalte hain; aur phir bhi, momentum $mv$ hai, jo poori tarah massive ions se dominate hota hai.

Error: yeh ideal single-ion picture hai. Real engines ionization cost, grid interception, aur imperfect neutralization mein power lose karti hain.

Kyunki grids ek electric field ke zariye act karte hain, aur ek neutral atom koi electric force feel nahi karta — tumhe pehle ise charged banana hoga taaki field ise pakad sake.

Har ionizing collision ek ion plus ek extra free electron produce karta hai; woh electron aur atoms ionize karta hai, isliye ek seed electron ek chain trigger karta hai.

Yeh continuously positive ions eject karti hai; har second positive charge khone se ship mein growing net negative charge reh jaata hai.

Ek negative ship electrostatically nikalne wale positive ions ko wapas kheeenchti hai, woh forward momentum cancel kar deti hai jo unhe carry karna tha.

Unka thrust (~0.1 N) ship ke Earth weight se bahut kam hai, isliye woh lift off nahi kar sakti; lekin space mein, mahino ki tiny push enormous $\Delta v$ add kar deti hai. Dekho Tsiolkovsky Rocket Equation.

Thrust momentum flow $\dot{m}{v}_e$ hai; bhaari mass slower speed ko zyada compensate karta hai, kyunki $F=I\sqrt{2mV/q}$ $m$ ke saath badhta hai.

Yeh seedha electrical work $qV$ jo ion par kiya gaya usse gained kinetic energy $\frac{1}{2}m{v}_e^2$ se equate karta hai, field ki shape ki koi details ki zarurat nahi. Dekho Work-Energy Theorem.

Specific impulse fuel economy capture karta hai (thrust per propellant used); ion engines wahan high score karte hain bhaale unka raw thrust tiny rehta hai. Dekho Specific Impulse and Exhaust Velocity.

Kyunki wider gap $d$ beam ke apne positive space charge ko zyada build up hone deta hai, current choke karta hai ($I\propto 1/d^2$); gap decide karta hai ions kitne crowded hote hain. Dekho Child-Langmuir Space Charge Law.

Thrust vanish ho jata hai: $F=I\sqrt{2mV/q}=0$. Akele voltage bina ions ke move kiye koi momentum flow produce nahi karta.

Spacecraft positive charge ho jati hai, jo phir electrons ko wapas attract karega aur kuch useful repel nahi karega — balance $I_{neutralizer}=I_{beam}$ dono taraf hold karna chahiye.

Har ion zyada energy gain karta hai ($v_e\propto \sqrt{q}$), lekin per unit current kam ions charge carry karte hain; doubly-charged ions aam taur par ek inefficiency hain, ionization energy waste karte hain bina matching thrust gain ke.

Nahi. Hardware limits ko ignore karte hue bhi, thrust extractable current par space-charge (Child–Langmuir) limit se cap hoti hai; $v_e$ badhta rehta hai lekin $I$ saath nahi de sakta. Dekho Child-Langmuir Space Charge Law.

Same voltage bahut zyada $v_e$ deta hai lekin har ion mein bahut kam momentum, isliye thrust drop ho jata hai — yahi wajah hai ki heavy inert xenon prefer kiya jata hai. Dekho Plasma Physics — Ionization Energy.

$I\propto V^{3/2}/d^2$ ke saath extractable current unphysically blow up hoti hai aur grids arc/short ho jaate — real engines ko ek finite gap chahiye, jo geometry limit ko fundamental dikhata hai.