Root mean square value ( r.m.s )

• Alternating current and voltage values fluctuate between zero and maximum potential , while direct current values remain steady . 
• In order to obtain the same values for A.C as are present in D.C , the r.m.s value is used . 
• The r.m.s. value of a current of 1A A.C gives the same heating effect as 1A D.C, and similar for A.C voltage . 
• The relationship of r.m.s. value to maximum value A.C is : 
• r.m.s. value / maximum value = 0.707 
• maximum value = r.m.s. value x 1.414 

Example :
(A) Calculate the maximum value of A.C. voltage when the r.m.s value is 240 V
(B) Calculate the r.m.s value of an A.C current which has a maximum value of 30 A .