is always less than that of either circuit alone. The reason for this is evident when we consider the expression for the resistance of a wire,   

The putting of two wires in parallel, in place of one of them, is equivalent to increasing the diameter of that one.

FIG .1

Demonstration. - Wind a coil of iron wire No. 18 and couple its ends to two binding posts A and B, Fig. 1. Measure its resistance. Wind a second coil of No. 18 copper wire, couple it to A and B and measure its resistance. Couple both coils to A and B and measure the combined resistance. The last resistance will be less than either of the others.

A careful study of the results of the above demonstration will help the student to understand the conditions which govern the resistance of parallel circuits.

To find an expression for the combined resistance of a circuit and its shunt, we can take the case of a galvanometer with its shunt (Fig. 1).

The current passing through the galvanometer may be written G=V/g ,  in which G is the current, g the resistance of the galvanometer V and the potential difference at its terminals. The current through the shunt may be written S=V/s.

The entire current will be I=V/R in which R is the combined resistance of the galvanometer and its shunt.  

In general, the parallel resistance of two circuits is the product of the two resistances divided by their sum. The parallel resistance of several circuits is found by finding the  value of R in the expression

In the case of any number of equal resistances, incandescent lamps for example, the parallel resistance of n lamps is    th the resistance of a single lamp. 

The arrangement shown in Fig. 2 is frequently used when we wish to measure a current greater than the galvanometer will carry safely. A shunt that will carry    of the current, so that the galvanometer will read  of the true value of the current, is called a tenth shunt.  

اخر الاخبار

اخبار العتبة العباسية المقدسة

بمشاركة 72 متسابقًا.. المجمع العلمي ينظم مسابقة قرآنية في بغداد

قسم الصناعات يباشر تصنيع أبواب خشبية لمكتبة ودار مخطوطات العتبة العباسية المقدسة

شعبة فاطمة بنت أسد تنظم زيارة إلى الراقدات في مدينة الإمام الحسين (عليه السلام) الطبية

قسم الإعلام يختتم الدورة الثانية الخاصة بالتصوير الفيديوي لمنتسبيه

المزيد

الآخبار الصحية

نصائح علمية لتقوية دماغك وتقليل التدهور العقلي

هرمون الذكورة يفاقم عدوى خطيرة تهدد حياة الرجال

سبب رئيسي للإصابة بسرطان القولون

بعد سن الأربعين.. هل أنت من الفئات المعرضة لخطر الغلوكوما؟

المزيد

الآخبار التكنلوجية

حرق الأمونيا.. كيف يساعد محطات الكهرباء في اليابان على إزالة الكربون؟

الشمس تقذف نتوءا عملاقا باتجاه قطبها الشمالي

كيف يخدع النعناع جسمك ليشعر بالبرودة؟.. صور عالية الدقة تكشف السر لأول مرة

ما الدور الذي يلعبه الـ AI في "حروب أميركا"؟

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