Tuesday, November 27, 2007

Capacitance

Capacitance is a measure of the quantity of electric charge stored for a given electric potential. The most general form of charge storage device is a two-plate capacitor. If the charges on the plates are +Q and -Q, and V gives the voltage difference between the plates, then the capacitance is given by c=Q/v. The capacitance of the majority of capacitors used in electronic circuits is several orders of size smaller than the farad. The most ordinary units of capacitance in use today are the millifarad (mF), microfarad (µF), the nanofarad (nF) and the picofarad (pF).

The dielectric constant for a number of very useful dielectrics changes as a function of the applied electrical field, e.g. ferroelectric materials, so the capacitance for these devices is no longer purely a purpose of device geometry. If a capacitor is driven with a sinusoidal voltage, the dielectric constant, or more exactly referred to as the dielectric permittivity, is a function of frequency. A changing dielectric constant with frequency is referred to as a dielectric dispersion, and is governed by dielectric recreation processes, such as Debye relaxation.

Monday, November 19, 2007

pregnant woman and her health

Pregnancy is not an easy job for a woman. Starting from conception to birth, a woman's body carries out the most miraculous process of fertilization, implantation and the maturity and growth of her baby . Her body is her baby's dwelling place for the next nine months and the occurrences of pregnancy turn into a journey of many new physical feelings. Whether it is first, second, thirdpregnancy, her body will respond in a different way to each individual pregnancy. So health of a pregnant woman is very important to be taken care of.

Throughout the first 12 weeks of pregnancy called the '1st trimester’, a woman's body adjust to present a fostering and protective environment for her baby to grow and develop. Seldom, the early signs of pregnancy can make a woman feel puzzled. This may be for the reason that many of the physical signs of in the early hours of pregnancy such as enlarged tender breasts, sensitivity of tiredness, overstuffed and perhaps experiencing spasms and or pelvic uneasiness can be considered as normal pre-menstrual signs. In all these stages the health of the woman declines because she is not only feeding herself, also her little developing fetus.

They may also sense disgusted or sick, due to morning sickness. It is not unusual to feel unsure about what is 'normal' during the early stages of pregnancy development, and unfamiliar signs or sensations may trigger concerns about the health, of her and baby. It’s been proved by the Gynecologists that every woman's body will react in a different way to being pregnant. Many women find their early pregnancy symptoms very difficult to cope with, both at work and generally.