Advertisements
Advertisements
प्रश्न
A capacitor is made of two circular plates of radius R each, separated by a distance d << R. The capacitor is connected to a constant voltage. A thin conducting disc of radius r<<R and thickness t << r is placed at a centre of the bottom plate. Find the minimum voltage required to lift the disc if the mass of the disc is m.
Advertisements
उत्तर
When the disc is in touch with the bottom plate, the entire plate is a equipotential. A change q′ is transferred to the disc.
The electric field on the disc is `V/d`
∴ q' = `ε_0 V/d pir^2`
The force acting on the disc is `- V/d xx q^' = ε_0 V^2/d^2 pir^2`
If the disc is to be lifted, then `ε_0 V^2/d^2 pir^2 = mg`
⇒ V = `sqrt((mgd^2)/(piε_0r^2))`
APPEARS IN
संबंधित प्रश्न
Obtain an expression for electric field intensity at a point outside uniformly charged thin plane sheet.
In the given circuit diagram a voltmeter ‘V’ is connected across a lamp ‘L’. Ho would (i) the brightness of the lamp and (ii) voltmeter reading ‘V’ be affected, if the value of resistance ‘R’ is decreased? Justify your answer.
A 5 V battery of negligible internal resistance is connected across a 200 V battery and a resistance of 39Ω as shown in the figure. Find the value of the current in circuit.
What is the permittivity of a medium?
When a dielectric is completely inserted between a capacitor’s plates, what does its dielectric constant represent?
Which description defines a dielectric?
Which unit and approximate value are given for the dielectric strength of air?
In the parallel plate capacitor reference state, what is assumed about the charge when the battery is disconnected?
What is the potential difference across the plates in the reference state without a dielectric?
Which expression gives the capacitance of the reference parallel plate capacitor without a dielectric?
What is the stated value of the permittivity of free space?
How is the net electric field related to the external field and the induced opposing field in a dielectric?
For a full dielectric slab filling the gap, how does the potential difference change?
What is the capacitance of an isolated parallel plate capacitor when a full dielectric slab of dielectric constant \[K\] is inserted?
Which expression connects the permittivity of a dielectric medium to the capacitance of a full-slab parallel plate capacitor?
How does the stored energy change when a full dielectric is inserted into an isolated capacitor with constant charge?
A dielectric slab with thickness \[t=\frac{3d}{4}\] and dielectric constant \[K\] is inserted into a gap of separation \[d\). What is the new capacitance in terms of the original capacitance \[C_0\]?
