Question

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 $5000$ electroplaques. The arrangement is suggestively shown below. Each electroplaque has an emf of $0.15\, V$ and internal resistance of $ 0.25\, \Omega $ . The water surrounding the cell completes the 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

Answer 1

Answer: (A)

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 $5000 \times 0.15=750\, V$
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 Ohm's law, $V=I R$
$\therefore I=\frac{V}{R}=\frac{750}{500+12.5}=1.46 A$
$\therefore I \approx 1.5 \,A$