A-Level物理的评分标准，物理考试如其它考试一样, 也采取全球标准化评分, 总分600分。 所有考试分为六个单元,其中 1、 2、 4、 5单元的卷面分值均为80分,标准化之后的满分为 120分; 第3、6两个实验单元卷面分值为 40分,标准化之后的满分为 60分。总成绩达到标准化分数 80%以上的即 A 等(480分以上) , B、C、D、E、U 分别对应总成绩的70-80%、60-70%、50-60%、40-50%及40%以下。
A capacitor is a device used to store charge.
They can also store energy, in the form of electrical energy due to the electrical field that is generated between the charged plates.
When in a circuit containing a cell and a resistor capacitors collect charge on these plates. One plate collects positive charge and the other collects negative charge. You may therefore say that a capacitors overall charge is 0 as the plates cancel out. Well not quite as when we talk about the charge a capacitor holds we refer to the amount on just ONE of the plates.
Circuit symbols for capacitors
They are made of two parallel metal plates which are separated by an insulting material called a dielectric. These are two types of main capacitor, electrolytic and non-electrolytic.
Electrolytic capacitors can store a greater amount of charge but are polarized (have a +ve and -ve lead) and therefore must be connected in the correct way. Reversing the polarities of an electrolytic capacitor results in their being damaged and possibly exploding.
Non-electrolytic capacitors store slightly less charge but are not polarized and can be connected anywhere in a circuit.