Electric Potential Energy vs. Electric Potential on the MCAT

Electric potential (V) and electric potential energy (U) regularly trip up MCAT students. Here, we’ll clear it up with explanations, tips, and helpful mnemonics. 

What Is the Difference Between Electric Potential Energy vs. Electric Potential?  

Let’s break down these concepts in an easy-to-remember way!

Electric Potential Energy (U)

This is energy stored due to the interaction between two charges.

Formula:‍

U=kQqrU = \frac{kQq}{r}U=rkQq​

• Q = source charge
• q = test charge
• r = distance between them
• k = Coulomb’s constant

Imagine two magnets. When you bring them closer, they either repel or attract each other—and you can feel that stored tension. That’s potential energy. If you let go, that energy might turn into motion (kinetic energy).

Electric potential energy works the same way. It's energy stored due to a spatial relationship between charges, ready to be converted into movement or work.

Key idea: This is actual energy. Think of it like the energy in a stretched spring or a lifted weight. It depends on both the source and test charge.

Electric Potential (V)

This is energy per unit charge at a point in space created by a source charge.

Formula:

‍V=Uq=kQrV = \frac{U}{q} = \frac{kQ}{r}V=qU​=rkQ​

Think of it like setting up a gravitational hill. You can describe how steep it is without knowing whether a rock is rolling down yet. That’s electric potential—it describes what would happen if a charge showed up.

Key idea: It’s the “electric landscape” created by the source charge. It doesn’t care if another charge is there yet, it just tells you what would happen if one showed up.

Here’s a rule of thumb to make this concept easier to remember:

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Real-Life High Voltage: Jurassic Park Example

The Jurassic Park fence is a great example. It’s labeled 10,000 volts. That means there’s a huge difference in potential between the fence and the ground (or the kid grabbing it). If a charge moves from the fence into the kid’s body, it releases tons of energy:

Energy=q⋅ΔV\text{Energy} = q \cdot \Delta VEnergy=q⋅ΔV

So if 3 Coulombs of charge move:

E=3⋅10,000=30,000 JoulesE = 3 \cdot 10,000 = 30,000 \, \text{Joules}E=3⋅10,000=30,000Joules

That energy surges into the body—and could stop a heart. This illustrates why voltage matters: it’s not just a number, it’s a measure of energy-per-charge waiting to be released.

Let’s summarize all of this information:

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MCAT Connections: What to Know for Test Day

Here is where these questions show up:

• Electrostatics: Fields, forces, and charge movement
• Circuits: Battery voltages, capacitors
• Work-energy problems: Calculating work done on/by a charge

Here’s your formula cheat sheet:

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Common MCAT Mistakes/Red Flags

Here is what constantly trips up students:

• Confusing U and V—they look similar but represent different things
• Forgetting that V is independent of the test charge
• Assuming all charges move from high to low potential—this only works for positive charges
• Misusing ΔV in work calculations: Use the right sign for q!
• Plugging in the wrong distance—remember r is always from center-to-center of charges

Final Thoughts

Electric potential is about where a charge is; electric potential energy is about how two charges interact. Know the difference, and you’ll unlock a key concept that shows up all over the MCAT.