Current Electricity and Electrical InstrumentHard
Question
The efficiency of a cell when connected to a resistance R is 60%. What will be its efficiency if the external resistance is increased to six times.
Options
A.80 %
B.90 %
C.55 %
D.95 %
Solution
η = 
= 1 − 
= 0.6 ⇒ R = 0.6 r + 0.6 R
r =
R = 
⇒ η = 
= 0.9 = 90%
= 1 − = 0.6 ⇒ R = 0.6 r + 0.6 Rr =
R = ⇒ η = = 0.9 = 90% Create a free account to view solution
View Solution FreeTopic: Current Electricity and Electrical Instrument·Practice all Current Electricity and Electrical Instrument questions
More Current Electricity and Electrical Instrument Questions
Two cities are 150 km apart. Electric power is sent from one city to another city through copper wires. The fall of pote...A battery consists of a variable number 'n' of identical cells (having internal resistance 'r' each) whi...Consider the following two statements. (A) Kirchhoff′s junction law follows from the conservation of charge (B) Ki...In a balanced wheat stone bridge, current in the galvanometer is zero. It remains zero when...A group of N cells whose emf varies directly with the internal resistance as per the equation EN = 1.5 rN are connected ...