Ohm's Law states that voltage is equal to current times resistance, or, V = IR. Solve the equation for current, I
, and substitute the known values, noting that 20k ohms is equivalent to 20,000 ohms: I = 1.5V/20,000ohms.
This yields an answer of amperes, but the answer choices only provide milliamperes. To convert amperes to milliamperes, use the conversion factor of 1 A = 1000 mA: 0.000075A x (1000 mA/1A) = 0.075 mA.
Note that the A's in the numerator and denominator cancel, leaving the desired mA; this technique is called dimensional analysis and proves extremely useful in verifying answers.