Variable capacitor, Physics

Assignment Help:

These capacitors are used as tuning capacitors in radio receivers. The two requirements of these capacitors are:

(1)         Frequency stability

(2)         Preventing micro phony

For frequency stability, the spacing between vanes should not change. For this the vanes are relived of all the internal stresses before assembly. To prevent micro phony, there must not be mechanical resonance over audio range of frequencies. At very high frequency (V.H.F.); vanes are either thick or widely spaced.

CONSTRUCTION: For tuning receiver and low power transmitters air dielectric capacitors are usual. A two-gang variable capacitor suitable for radio receivers contains two variable capacitors operated to a single tuning control. The various parts of a capacitor are: Frame, rotor, stator spindle and bearing. In this construction, fixed metal plates or vanes connected together form a stator and movable vanes connected together from a rotor. Capacitance is varied by rotating the shaft to make the rotor plates mesh with the stator plates. The fixed vanes are insulated from the frame work of capacitor by mounting which are made of ceramic materials. The movable vanes are spaced on the spindle by spacing washers to that they do not touch the fixed vanes at the point. Full mesh of the two sets of vanes means maximum capacitance. Moving the rotor completely out of mesh provide minimum capacitance. Losses in such air dielectric capacitors are small. The power factor at 1.5 MHz may be as low as 10-4 corresponding to a Q of 10000. Variable capacitors may be having their capacitance intestinally and rapidly change over the life of the device. They include capacitors that use a mechanical construction to change the distance between the plates, or the amount of plate surface area which overlaps, and variable capacitance diode that change their capacitance as a function of the applied reverse bias voltage. Variable capacitance is also used in sensors for physical quantities, including microphones, pressure and hygrosensors.


Related Discussions:- Variable capacitor

Electricity, two charge(q) each are kept 1m apart, where should third charg...

two charge(q) each are kept 1m apart, where should third charge be placed in order to get third charge -q/4

Young two slit interference experiment, If Young' two slit interference exp...

If Young' two slit interference experiment is done with white light what could be seen?

WEDGE CONSTRAINTS, HOW TO MARK DIRECTION OF ACCELERATION TO APPLY WEDGE C...

HOW TO MARK DIRECTION OF ACCELERATION TO APPLY WEDGE CONSTRAINTS ..

What is applied force, Applied Force (Fapp) : an applied force is a force t...

Applied Force (Fapp) : an applied force is a force that is useful to an object by a person or another object. If a person is approaching a desk across the room, there is applied fo

Determine the pd across the resistor, An alternating voltage v=250sin800t v...

An alternating voltage v=250sin800t volts is applied across a series circuit having a 30 resistor and 50µF capacitor. Calculate (a) the circuit impedance, (b) the current ?

Find the minimum angle at which a roadbed should be banked, Find the minimu...

Find the minimum angle at which a roadbed should be banked Determine the minimum angle at which a roadbed should be banked so that a car traveling at 20.0 m/s can safely negotia

Determine the magnitude of the pointing vector, A laser beam from 200 watt ...

A laser beam from 200 watt source is focused on an area of 10 -8 m 2 . Determine the magnitude of the Pointing vector of the area.

Draw a possible configuration of nodes and cells - 2d shape, Consider the 2...

Consider the 2D shape below. Draw a possible configuration of nodes and cells (at least 15) that could be used to solve for the temperature distribution. Provide equations that wou

Michealson interferometer, describe the principle, construction and working...

describe the principle, construction and working of Michelson Interferometer.

How can we increase current sensitivity of a galvanometer, Q. How can we in...

Q. How can we increase the current sensitivity of a galvanometer? The current sensitivity of a galvanometer is able to be increased by (i) Rising the number of turns (ii

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd