AP Physics B : Understanding Resistors and Resistance
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Example Questions
Example Question #11 : Electricity And Magnetism
Which of the following changes to a copper wire will lead to the greatest decrease in voltage?
Increasing the length of the copper wire by a factor of two
Increasing the current through the copper wire by a factor of two
Increasing the cross-sectional area of the copper wire by a factor of two
Replacing the copper wire with a more conductive material
Increasing the cross-sectional area of the copper wire by a factor of two
According to Ohm’s law a decrease in current and/or resistance will lead to a decrease in voltage, since voltage is directly proportional to both current and resistance.
Increasing the current will not decrease voltage. Remember that resistance is defined as:
In this formula, 
The only answer that will lead to a decrease in voltage is the choice to increase the cross-sectional area of the wire.
Replacing the copper wire with a more conductive material will increase the resistivity, which will subsequently increase resistance and voltage.
Example Question #2 : Electric Circuits
A student assembles a circuit made up of a voltage source and two resistors. All three circuit elements are connected in parallel. The voltage across the voltage source is 
The current through the 
The voltage across the 
The voltage across the 
The current through the 
The voltage across the
When circuit elements, such as resistors, are connected in parallel they will have the same voltage drop. The current through the 
Since voltage is the same across resistors, the lower resistance (
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