PhysicsAdvancedHigh School (11–12)Electricity & Magnetism › Electric Potential and CapacitanceJEE AdvancedOlympiad
Created by StemPy LabA point charge is fixed at , and a point charge is fixed at , from . Nothing else is nearby, and the potential is zero at infinity. Along the line the potential is zero at a point from , between the charges. But the points of zero potential do not lie only on that line. Taken together, at finite distances, they form one closed surface. Think about its shape, its size and where its centre lies. Which statement describes that surface?
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← A parallel-plate capacitor has air between its plates, which are 6.0 mm apart. It is charged to 90 V and then taken off the battery. Two flat pieces are now slid into the gap, parallel to the plates, as in the figure. One is a slab of dielectric constant 3.0 and thickness 3.0 mm. The other is an uncharged metal sheet of thickness 1.5 mm. They do not touch each other or the plates, and they cover the plates fully. Ignore the effects at the edges. What is the potential difference between the plates now?In a vacuum diode, a hot flat cathode at x = 0 gives off electrons. They cross to a flat anode at x = d = 4.0 mm, which is held at 200 V above the cathode. The electrons leave the cathode almost at rest. A steady stream of them fills the gap, and their charge changes the potential there. Between the plates it is V(x) = V₀(x/d)^(4/3), V₀ = 200 V The plates are large, so V depends on x only. Take ε₀ = 8.85 × 10⁻¹² C² N⁻¹ m⁻². What is the total charge in the space between the plates, per square metre of plate? →
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