Electrostatics on the MCAT

POV: you reach out to touch a doorknob and, all of a sudden, you are rudely interrupted by a static shock. This is where static electricity comes into play. This occurs when extra electrons (negatively charged particles) jump from your body to the doorknob. 

Another example is, when you rub your shoes on the carpet, excess electrons can transfer from the carpet to your body. As you reach out to touch the doorknob, electrons jump from your body (the more negative end) to the doorknob (the more positive end). This phenomenon of jumping of electrons is what creates the annoying static shock and the scary thunderstorms. 

Now that we have gone through a well known example of electrostatics at play, we can dive a little further into looking at key terms, definitions, and topics that will be important for the MCAT

Let’s get started!

Electrostatics on the MCAT: What You Need to Know

Physics will make up 20-30% of the Chem/Phys section of the MCAT.

Specifically, electrostatics is considered medium-yield and comes up primarily in passage-based questions within the context of electrical circuits and instrument design. 

This is not to say, however, that questions on electrostatics will not come up as fundamental discrete questions as well. In particular, simple electrostatics calculation questions (e.g. calculating electrostatic force, electric field, etc.) will be a medium-yield topic within fundamental discrete questions as well. 

Luckily for you, this review will give you a concise yet comprehensive review of electrostatics you are required to understand! 

Let’s get started!

Important Sub-Topics - Electrostatics 

Charged Particles 

Like mass and density, electric charge is a physical property of matter. The elementary charges are protons and electrons. Protons carry a +1.6 x 10-19 C, while electrons carry a -1.6 x 10-19 C and charge. The SI unit for electric charge is the coulomb (represented by ‘C’) and is a scalar quantity. 

Conductors, unlike insulators, are materials that easily allow the movement of charge throughout. When there is an excess build-up of charge, specifically electrons, placed on a conducting object a potential difference is generated, resulting in the repulsion of like charges and the movement of electrons to the positive end of the potential difference. This flow of charge is called an electric current.

The law of conservation of charge states that electrical charge cannot be created nor destroyed within a closed system. However, this does not mean that it is impossible to create or destroy protons or electrons. 

Electric charge is carried by electrons and protons which can be created and destroyed. However, the law of conservation of charge states that positive and negative charges can transfer from one area to another, but the net charge of a closed system stays the same. 

(Coming Soon!) Full Study Notes : Charged Particles

For more in-depth content review on charged particles, check out these detailed lesson notes created by top MCAT scorers. 

Coulomb’s Law

Coulomb’s Law states that the magnitude of the electrostatic force of attraction or repulsion between two point charges is directly proportional to the product of the magnitude of charges and inversely proportional to the square of the distance between the two point charges.

Coulombs Law

If Coulomb’s law gives a positive result, this means that the force between the point charges is repulsive. However, if Coulomb’s law gives a negative result this means that the two point charges are attracted to each other. 

(Coming Soon!) Full Study Notes : Coulomb's Law

For more in-depth content review on coulomb's law, check out these detailed lesson notes created by top MCAT scorers. 

Electric Fields

An electric field (E)  is a region in which a charge will feel a force. More specifically, it is defined as the amount of electrostatic force (F) that is felt by a charge(q) of +1C. 

F = E x q

Electric fields are vectors, where positive charges will experience electrostatic force in the same direction as the electric field, and negative charges will experience electrostatic force in the opposite direction to the electric field. 

(Coming Soon!) Full Study Notes : Electric Fields

For more in-depth content review on electric fields, check out these detailed lesson notes created by top MCAT scorers. 

Distinction between Electric Potential Energy and Electric Potential

Electric potential energy is the energy required to move a charge against the electrostatic force brought on by an electric field. Electrical potential energy can be gained by moving a charged particle against the electrostatic force brought on by an electric field. 

On the other hand, electric potential is the amount of work per unit charge required to bring a charge from infinity to a point within an electric field. The concept of electric potential is used to express the effect of an electric field on a point charge in terms of its location within the electric field. The electric potential difference, or the difference in electric potentials between two points in an electric field is termed voltage.

Electric Potential = Potential Energy / q

For more in-depth content review on distinction between electric potential energy and electric potential, check out these detailed lesson notes created by top MCAT scorers. 

Important Definitions and key Terms - Electrostatics on the MCAT 

Term

Definition

Electric Charge

A basic property of matter that is carried by elementary particles (electrons & protons), which govern how the particles will be affected by an electric or magnetic field.

Conductors

Materials that easily facilitate the flow of electrons through it ( i.e. it conducts electricity).

Insulators

Materials that do not impede the flow of electrons (i.e. the flow of current) through it.

Electric Potential Difference

The work/change in potential energy required to bring a point charge of +1 from one location to another within an electric field.

Electric Current

The flow of charged particles (electrons or ions) through an electrical conductor or space.

Law of Conservation of Charge

States that the net charge within a closed system remains the same.

Point Charge

A hypothetical charge, of some magnitude, located at a single point in space.

Electric Field

Originates from electric charges and exert either attractive or repulsive forces on other charged particles.

Electrostatic Force

The force of attraction or repulsion between point charges or from an electric field.

Electric Potential Energy

Energy/work required to move a charge against an electric field.

Electric Potential

The amount of work per unit charge required to bring a charge from infinity to a point within an electric field.

Voltage

The difference in electric potential between two points.

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