In the five-year primary school natural tenth book "Electric Heat", according to the requirements of the book, a wire is connected to the two poles of the battery, and then the wire is touched by hand, and the wire is heated, indicating that the current is passed through the wire to make the wire Get angry and get to know the electric heat. Personal experience of electric heating is the main advantage of this experimental design. However, the fly in the ointment is that because the electric energy of a dry battery is very limited, the electrical resistivity of the wire is relatively large, but the heat generated is very small. The feeling of heat is not obvious when the wire is touched by hand. Besides, the temperature of each person's hand is definitely not the same at the time, and the feeling after touching is definitely not the same. Some already feel hot, and some feel cold. Moreover, different people have different degrees of sensitivity to low external temperatures. In this way, students pass the experiment, and some have already felt the electric heat. He can say that the heat is generated when the current passes through the conductor, and some does not feel the electric heat. He thinks that the current does not generate heat when passing through the conductor. These two types of students each have their own opinions, and they all have their own reasons. It is also difficult to draw conclusions at one time.
After class, I meditate on how to solve this problem. The electric heat is due to the heat generated by the current passing through the conductor. Is it related to the heat conduction we have learned before? Can we use the experimental equipment for heat conduction used before? So I tried to stick the match to the wire with Vaseline, and then connect the two ends of the wire to the two poles of the battery. The match was shaken off due to the wire swaying during the connection. So I decided to connect the two ends of the wire to the two poles of the battery, and then stick the match on the wire. When I connected the wire and prepared to stick the match to the wire, I found a little bit stuck on the wire. Vaseline melted. I think if you use a few small pieces of Vaseline on the wire, the effect may be better. So I put this idea into practice. I got a few small groups of Vaseline and glued it to the wire. At the beginning, these groups of Vaseline were fixed there. Shortly after energizing the ends of the wire, Vaseline began to melt slowly and slowly slide down along the wire (the battery was held upright, with Vaseline attached) The wire is also vertical). This experimental phenomenon is very obvious.
When I used this experimental device in the classroom, the students responded very enthusiastically. "I saw it." "It's really hot." "Vaseline slipped down."... Such an experimental setup is very easy for students to read and easy to understand. When students see this experimental device, they naturally think of the experiments of heat conduction that they have learned before. This also helps students to consolidate the knowledge they have learned before, and it is easier to learn new knowledge based on the understanding of previous knowledge. .
However, the experiments in the book also need to be done and must be done first. If you can feel the electric heat yourself, of course it is better. Therefore, these two experiments complement each other and complement each other.
Nanxia S Central Elementary School (213166), Wujin City, Jiangsu Province. Based on the knowledge of secrets, balance, small windmills, wind power and wind direction, students in the third grade of elementary school have used some common materials to make some small technological productions. To enhance their ability to apply knowledge and inquiry.
The following describes a simple small boat production.
Scissors, single-sided tape paper, plastic water bottles with lids (cylinders), cardboard, straws (straight tubes, elbows), plasticine 1. Boats for making small sailboats body. Cut the mineral water bottle to the left as shown on the left: sail and mast. Take a straight straw as a mast, cut it into a triangular Baocui-shaped sail with hardboard paper (you can make two sails), and fix the sail and the mast with a single-sided tape, as shown in Figure 3. 3. Make the rudder. Cut one end of the curved straw into a socket, use it as a plastic piece cut from the hull, cut out the "small rudder", then insert the straw socket and use the tape paper.
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