AP Physics C: Electricity and Magnetism Flashcards: Resistance, Resistivity, and Ohm's Law
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Review key ideas with interactive flashcards. This set includes 10 cards to help you master important concepts.
What is Ohm's Law?
Ohm's law states that the current through a conductive element is directly proportional to the potential difference across it and inversely proportional to its resistance ($I=\frac{\Delta V}{R}$).
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What is Ohm's Law?
Ohm's law states that the current through a conductive element is directly proportional to the potential difference across it and inversely proportional to its resistance ($I=\frac{\Delta V}{R}$).
How do the physical properties of a uniform resistor determine its resistance?
The resistance of a uniform resistor is directly proportional to its resistivity and length, and inversely proportional to its cross-sectional area.
To decrease the resistance of a wire of a given material, should you make it thicker or thinner?
You should make it thicker. Resistance is inversely proportional to the cross-sectional area (A), so a larger area results in lower resistance.
What distinguishes resistance from resistivity?
Resistivity (ρ) is an intrinsic property of a material, while resistance (R) is an extrinsic property of a specific object that depends on its material, length, and area.
A potential difference of 12V is applied across a resistor, resulting in a current of 3A. What is the resistance?
The resistance is 4 ohms, calculated using Ohm's Law rearranged as $R = \Delta V / I$.
How is the total resistance calculated for a resistor whose resistivity varies along its length?
The total resistance is found by integrating along the length of the resistor using the equation $R=\int\frac{\rho(l)dl}{A}$.
According to Ohm's Law, what is the relationship between current and potential difference if resistance is held constant?
Current is directly proportional to the potential difference; if the potential difference doubles, the current will also double.
If a wire's length is doubled while its cross-sectional area remains constant, how does its resistance change?
The resistance will double, because resistance is directly proportional to the length of the object ($R=\frac{\rho l}{A}$).
State the formula for the resistance of a resistor with uniform geometry.
The formula is $R=\frac{\rho l}{A}$, where ρ is resistivity, l is length, and A is the cross-sectional area.
When is it necessary to use the integral form, $R=\int\frac{\rho(l)dl}{A}$, to calculate resistance?
This form is necessary when the resistor is made of a material whose resistivity, ρ(l), is not uniform but varies along the length of the resistor.