Chapter 3, Problem 2RP

If the current drops to 10 mA under the same conditions stated in the example, what is the voltage?

To determine

Find out the new voltage source value when the current in the ammeter drops suddenly from 50 mA to 10 mA.

Answer to Problem 2RP

The new voltage source value is 5 V.

Explanation of Solution

Calculation:

From the example problem 3-2 in the textbook, when a resistive circuit has 25 V source voltage, an ammeter reads 50 mA, and given that the current is suddenly drops to $10\text{ mA}$.

Calculate the percentage of current drop in original value as,

$\frac{10\text{mA}}{50\text{mA}}\times 100=20\%$

As the current drops 20 % of original value, the source voltage also must be change to $20\%$ of the original value. Thus the new voltage is,

$\begin{array}{l}20\%\times 25=0.20\times 25\\ 20\%\times 25=5\text{V}\end{array}$

The required voltage source to obtain the current of 10 mA is 5 V.

Conclusion:

Thus, the new voltage source value is 5 V.