A current of one quarter ampere may be written as:

First, we convert the fraction to a decimal: 'one quarter ampere' is equal to 0.25 amperes (A). The prefix 'milli' (m) means one-thousandth (1/1,000) of a base unit. Therefore, there are 1,000 milliamperes in a single ampere. To convert from the base unit (amperes) to a smaller unit (milliamperes), you multiply the value by 1,000. Multiplying 0.25 by 1,000 yields 250 milliamperes (mA). Other options are incorrect because they either use the wrong metric prefix, such as microamperes (which would be 250,000 µA), or they fail to multiply the 0.25 value by 1,000.