We have seen how an electric current is generated as a result of chemical action in a cell or battery. We have studied also a second method of generating a current by the use of a generator or dynamo. A third method is as follows:

Demonstration. - Twist together the ends of a small iron wire and a small copper wire and couple the other ends to the terminals of a sensitive galvanometer. Apply the heat of a Bunsen burner to the twisted ends of the wires and a movement of the galvanometer needle will indicate an electric current. Let the heated ends of the wires cool and the needle will return to zero. Hold a piece of ice against the twisted wires and the needle will move in the opposite direction.

The two wires as used in this demonstration form a thermoelectric couple. Such a couple will generate an electric current as long as the twisted ends of the wires differ in temperature from the ends coupled to the galvanometer. An extensive use of this current is made in the thermoelectric pyrometer, which is valuable in various industrial operations.

When this instrument is used for temperatures not to exceed 1800° F. (982° C.) the wires are made of nickel alloys and the couple is called a base metal couple. The wires are welded together at one end and are separately inclosed in porcelain insulating tubes as shown in Fig. 1. When in use they are inclosed in an outer protecting tube. 

For high temperatures the thermo-couple wires are one of platinum and the other of platinum alloyed with ten per cent of rhodium. This form can be used for temperatures as high as 2900° F. (1593° C.). High temperature pyrometers are used in measuring the temperature of furnaces, through the wall of which they are inserted.

The reading instrument is a form of millivoltmeter in which the scale is calibrated in degrees Fahrenheit or Centigrade as required. This instrument with its cover. removed to show its interior construction is shown in Fig. 2.

اخر الاخبار

اخبار العتبة العباسية المقدسة

العتبة العباسية المقدسة تعلن تأجيل مؤتمر معالم الحياة الطيبة عند أهل البيت (عليهم السلام) الدولي الثاني

قسم العلاقات العامة يقيم أمسية رمضانية ثقافية لطلبة الأقسام الداخلية في جامعة بابل

قسم الشؤون الفكرية ينظم ختمة قرآنية رمضانية في دولة تشاد بإفريقيا

ضمن مشروع بيوت النور.. المجمع العلمي ينظّم أمسية قرآنية رمضانية في كربلاء

المزيد

الآخبار الصحية

الماء المملح.. فائدة حقيقية أم "صيحة زائفة"؟

عادة بسيطة تدعم الصحة وتحافظ على الوزن المثالي

الغذاء النباتي يقلل مخاطر السرطان.. مع استثناء مهم

الحليب قليل أم كامل الدسم.. أيهما أفضل؟

المزيد

الآخبار التكنلوجية

أنثروبيك تتحدى البنتاغون.. وترامب يأمر بوقف التعامل معها

ميزة جديدة من "إنستغرام" لحماية المراهقين من الانتحار

الأولى من نوعها.. "تقنية مذهلة" في هاتف سامسونغ الجديد

لماذا تشعر المرأة بالألم أكثر من الرجل؟.. دراسة تجيب

المزيد

مواضيع ذات صلة

The Poles of a Cell

Size and E. M. F. of a Cell

Parallel Grouping

Ohms Law

Internal Resistance of a Cell

Unit of Electromotive Force, the Volt

Arrangement of Cells in a Battery; Series Grouping

The Laws of Resistance

The Unit of Resistance

The Unit of Current the Ampere

Electro-motive Force, Current, Resistance.

The Dry Cell