Electrostatic levitation (ESL) is a laboratory method developed at JPL for conta

Question

Electrostatic levitation (ESL) is a laboratory method developed at JPL for container-less processing of metal alloy under high-vacuum conditions (Pressure P~10-8 Torr). The ESL, apparatus layout is shown in Fig-1. It used a CCD camera array connected by a LabView controlled feedback. Loop (Fig.-2), to apply the high electrostatic potentials (Vapplied) to levitate small metal alloy specimens, with mass m ~ 30 mg, between two copper electrodes inside the cylindrical high vacuum chamber (See Fig.-3, Fig.-4). While levitated, the mg-sized specimens are melted using a high-power laser (Fig.-5). In this problem, estimate the charge, qm, required to levitate a Ti3,Zr13Cu47Ni8 (at.%) bulk metallic glass-forming specimen (Fig.-5). Measurements show that a potential difference of Vapplied = 12 kV is required to levitate the specimen against the force of gravity. 1/2-way between the two copper electrodes, that are spaced 10 mm apart. Calculate the magnitude of the electric field E, acting on the levitated specimen, and the charge present on the metals surface, q8; where this charge is supplied by a high-power deuterium arc lamp used to irradiate the specimen with ultra-violet wavelength light (See Fig.-1). Choose one of the answers shown below.

Explanation / Answer

V = 12 x 10^3 V , d =10mm = 10 x 10^-3 m

m = 30mg = 30 x 10^-6 kg
V = E.d

E = V /d   = 12 x 10^3 / 10 x 10^-3 = 12 x 10^5 V/m

ELectric force = GRavitational force

qE = mg

q x 12 x 10^5   = 30 x 10^-6

q = 245pC

Ans (c)

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