F5物理問題疑難

1)電勢差同電動勢有咩分別?
"Potential difference"(電勢差), as the name implies, is the difference in potentials between two points.
"Electromotive force"(電動勢), strictly speaking, is not a "force". It is a "voltage" that drives current through a circuit, as if there is a "force" that moves charges (or electrons) to flow. Hence, electromotive force (emf) is used on a power source, e.g. batteries or generators.
2)心臟起博器(pacemaker)如何應用了放射同位素?
Pacemakers need batteries to operate. Hence, after a number of years' operation, the batteries have to be replaced. This causes inconvenience to the patient as replacing of battery needs to be performed in hospitals.
If nuclear battery is used in pacemaker, replacement of battery need not be done because of the long operation life of these nuclear batteries.
Common isotopes used in nuclear batteries are alpha emitters. These isotopes have long half-lives so that they can supply power for many many years without any replacement. One of the isotopes used in early nuclear battery was plutonium-239 with half-life of 24 000 years. Other isotopes used may include promethium-147 or strontium-90 (half-life 29 years).
Since there are tremendous amount of heat produced in radioactive decay, this amount of heat is utilized in an thermopile (i.e. a thermocouple) to produce electric current. There are also other designs, such as those using a capacitor to store up the charges, that come from the emitted alpha or beta particles, to produce electricity.
You may refer to the following web-page for more information:
http://en.wikipedia.org/wiki/Atomic_battery

1) * 电动势定义为非静电力做功与电荷量的比值；电势差定义为静电力做功与电荷量的比值。前者衡量产生电能（非静电能转化为静电能）的能力；后者衡量消耗电能（静电能转化为非静电能）的能力。
* 在一般的电路中，电动势的积分路径是在电源当中，电势差则是沿着外电路积分。在数值上，电动势等于路端电压。