Final answer:
Increasing resistance with constant voltage will decrease the current due to Ohm's law. Doubling the voltage in an ohmic resistor doubles the current, and changing the resistance in one branch of a parallel circuit does not affect the other branches.
Step-by-step explanation:
If the voltage is constant and the resistance is increasing, the current will decrease according to Ohm's law, which states that current I is equal to voltage V divided by resistance R (I=V/R). Thus, increasing the resistance while holding the voltage constant will lead to a decrease in current.
Considering the practice problems, if you double the voltage across an ohmic resistor, the current through the resistor will double as well (answer a), which is in accordance with Ohm's law stating that current is directly proportional to voltage when resistance remains constant.
When two identical resistors are connected in parallel and you increase the resistance of one resistor, the current through and the voltage across the other resistor will remain the same. This is because in a parallel circuit, the voltage across resistors is the same and independent of changes in other branches.