# Physics

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The internal resistance of a dry cell increases gradually with age, even though the cell is not used. The emf, however, remains fairly constant at 1.5 V. Dry cells must be tested for age at the time of purchase by connecting an ammeter directly across the terminals of the cell and reading the current. The resistance of ammeter is so small that the cell is practically short-circuited. (a) The short-circuit current of a fresh No. 6 dry cell (1.5 V, emf) is 25 A. What is the internal resistance? (b) What is the internal resistance if the short circuit current is only 10 A? (c) The short circuit current of a 6 V storage battery may be as great as 1000 A. What is its internal resistance?

ok..I am confused are we suppose to use the V=E-Ir? I don't know what equation to use!

• Physics - ,

Ohm's law can be stated as:
(resistance in ohms)= (voltage in volts)/(current in amps) .

For part (a):
resistance=(1.5V)/(25A)=0.06 ohms

Use the same equation for (b) and (c).