(O Level Phy) The current from an electric eel

In solving complicated electric circuit problems, we often need to simplify the circuits step by step. Let’s apply this in an exotic question on an electric eel.

Draw the circuit and then simplify it step by step... 

Question:

The electric eel lives in rivers of South America. They kill their prey by electric shocks. Their “battery” is found in their large tail which contains a circuit of 700 000 special electricity-generating cells. The circuit consists of 15 parallel branches and each branch is a series of 47 000 special cells. Each cell produces a voltage of 0.15 V. Assume that there is a resistance of 0.25 Ω connected in series to each cell. The water around the eel is 800 Ω. Calculate the current generated by the electric eel.

[Solution]

Let's draw the circuit and simplify it step by step.

Total voltage across the circuit

= 47 000 x 0.15 V

Total resistance in each branch

= 47 000 x 0.25 Ω

Effective resistance of the circuit in the tail

= [15/(47 000 x 0.25)]^-1

= (47 000 x 0.25)/15

Total resistance

= effective resistance + water resistance

= (47 000 x 0.25)/15 + 800

Current

= V/R

= (47 000 x 0.15 V) / [800 + (47 000 x 0.25)/15] Ω

= 4.5 A

This following question is not related to the above question. Try this question before checking with the answer.

The special cells are arranged in lines in the electric eel's tail. Each line consists of 6000 special cells connected in series. The voltage across its body is 600 V.
(a) Calculate the voltage across each special cell.
(b) Calculate the current through the surrounding water if the water has a resistance of 600 Ω. An electric current of 0.2 A can kill a person. Can the current from the electric eel kill a person?


Answer: (a) Voltage across each special cell = 600 V ÷ 6000 0.1 V (b) I = V/R = 600 V/600 Ω = 1 A. This current is greater than 0.2 A and therefore can kill a person.