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

What is the v of he gas, At what temperature would the average speed of hel...

At what temperature would the average speed of helium atoms equal (a)the escape speed from Earth, 1.12 ´ 10 4  m/s, and (b) the escape speed from the Moon, 2.37´ 10 3  m/s? (See Ch

Principles of radiation therapy, Principles of radiation therapy: The ...

Principles of radiation therapy: The basic principle of radiation therapy is to maximize damage to the tumor while minimizing damage to the normal tissue.Factors that determin

What evidence suggests that light is a wave, 1. What evidence suggests that...

1. What evidence suggests that light is a wave? What evidence suggests that light is a particle? 2. In what sense does the "information age" depend on the bending of light?

Application for Subject Matter Expert in Physics., Hello! I would like to a...

Hello! I would like to ask if there is a job in Physics which is 24/7 Question Answering/problem solving and if any, I would like to apply for it. Thank You Prerak Dhawan

How the wavelength of monochromatic light is calculate, Briefly explain how...

Briefly explain how the wavelength of monochromatic light is calculated using Newton's rings arrangement?

New potential difference, A parallel plate capacitor has plates of area 200...

A parallel plate capacitor has plates of area 200 cm 2 and separation among the plates 1.00 mm. What potential difference will be manufactured if the charge of 1 nC is given to th

State zeroth law , When two objects A and B are in thermal equilibrium with...

When two objects A and B are in thermal equilibrium with a third object (C) independently, then they (i.e. A and B) are in thermal equilibrium equally i.e. Therefore, the t

Define the temperature and pressure conditions, What is the name of the tem...

What is the name of the temperature and pressure conditions at which water can be in the solid, liquid and gas phases simultaneously? Ans: The name of the temperature and pr

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