It is believed that many people may have such an unpleasant experience that when you need a flashlight, the flashlight can be found but cannot find the battery to light it, if flashlight also can emit light without the help of battery, such unpleasant experience will not occur any longer. Recently, AnnMakosinski, a 15-year-old girl from Canada, invented an eco-friendly flashlight; it can emit light without the use of battery. The flashlight works in accordance with the thermoelectric effect; it is powered by the heat of user's hand and the environmental temperature heat. How...