To decrease the range of an ammeter, its resistance needs to be increased. An ammeter has resistance R₀ and range I. Which of the following resistances can be connected in series with it to decrease its range to I/n?
A. R₀ / n
B. R₀ / (n - 1)
C. R₀ / (n + 1)
D. None of these

To decrease the range of an ammeter to I/n, you need to add an external resistance in series with it. The total resistance of the combination should be R_0/n.

So, you need to find an expression for the external resistance (R_ext) that, when added in series with the ammeter's resistance R_0, results in a total resistance of R_0/n.

Therefore, R_ext + R_0 = R_0/n

Subtracting R_0 from both sides:

R_ext = R_0/n - R_0

Now, factor out R_0:

R_ext = R_0 * (1/n - 1)

To simplify further:

R_ext = R_0 * [(1 - n)/n]

So, the correct answer is:

A. R_ext = R_0/n

So, you should connect a resistance of R_0/n in series with the ammeter to decrease its range to I/n.