question_answer

Eels are able to generate current with biological cells called electroplaques. The electroplaques in an eel are arranged in 100 rows, each row stretching horizontally along the body of the fish containing 5000 elecrroplaques. The arrangement is suggestively shown below. Each electroplaques has an emf of 0.15 V and internal resistance of 0.25\[\Omega \]. The water surrounding the eel completes a circuit between the head and Its tail. If the water surrounding it has a resistance of 500\[\Omega \], the current an eel can produce in water is about:

A) 1.5 A         

B)                       3.0 A                     

C)       15 A                      

D)       300 A

Correct Answer: A

Solution :

Key Idea: Find the equivalent circuit of consisting of net emf, net resistance. In each row all the 5000 electro-plaques are connected in series and all the 100 rows are connected in parallel. Hence, equivalent emf is \[5000\times 0.15=750V\] Equivalent resistance \[=0.25\times 5000\] \[=1250\Omega \] Now, the circuit of eel is redrawn as, Voltage across resistors connected in parallel is same, also equivalent resistance is \[\frac{1250}{100}=12.5\Omega \] From Ohms law, \[V=IR\] \[\therefore \]    \[I=\frac{V}{R}=\frac{750}{500+12.5}=1.46A\] \[\therefore \]     \[I\approx 1.5A\]