5. Electrostatics and Magnetism EQUATIONS

Question 1

5 (Equation) What is the equation for Coulomb’s Law?

I.E. The electrostatic force between two charges.

Answer 1

F_e= the electrostatic force between two charges
k= Coulomb’s constant
q₁ & q₂= the magnitude of the two charges
r= distance between charges.

** it’s important to note that force will change by a magnitude of distance squared when they forces are separated.

Very similar to the equation for gravitational force

Question 2

5 (Equation) What is the equation for the magnitude of an electric field?

Or electric field magnitude

Answer 2

E= the electric field magnitude in newtons per coulomb
F_e= magnitude of the force felt by the test charge q
q= test charge
k= electrostatic constant 8.99×10⁹ (N⋅m²)/C²)
Q=is the source charge magnitude
r= distance between the charges

Key Concept: by dividing coulomb’s law by the magnitude of the test charge, we arrive at two ways of determining the magnitude of the electric field at a point in space around the source charge.

Note: the second equation does not require a test charge.

Question 3

5 (Equation) What is the equation for electric potential energy?

POTENTIAL ENERGY
not
ELECTRIC POTENTIAL

Answer 3

U= electric potential energy

k= electrostatic constant 8.99×10⁹ (N⋅m²)/C^²

Q= the source charge magnitude= electron x (e=1.6x10^-19 C)

q= the test charge magnitude = electron x (e=1.6x10^-19)

r= radius

Question 4

5 (Equation) What is the equation for the electric potential?

Answer 4

V= electric potential measured in volts (V) (1 V = 1 J/C)

U= electric potential energy

q= the test charge magnitude = electron x (e=1.6x10^-19 C)

Q= the source charge magnitude= electron x (e=1.6x10^-19 C)

k= electrostatic constant 8.99×10⁹ (N⋅m²)/C²

²

Question 5

5 (Equation) What are the four equations that you should know for the MCAT based off of coulomb’s law?

Answer 5

From left to right, multiply by R
From top to bottom, divide by q

Question 6

5 (Equation) What is the equation of a magnetic field from a wire (straight wire)?

Answer 6

B= magnetic field
r= distance from the wire
µ ₀= permeability of free space
I= current

Question 7

5 (Equation) What is the equation of a magnetic field for a loop wire?

Answer 7

B= magnetic field
r= distance from the wire
µ₀= permeability of free space
I= current

Note, it is the same equation, just without the pi.

This gives the magnitude of the magnetic field only at the center of the circular loop of current carrying wire with a radius r.

Question 8

5 (Equation) What is the equation for the magnetic force exerted on an object moving by?

Answer 8

F_b=qvBsinӨ

• F_b= the magnetic force
• q= the charge of the moving object
• v= the velocity of the moving charge
• B= magnitude of the magnetic field
• Ө= the smallest angle between the velocity vector and the magnetic field.

Question 9

5 (Equation) What is the equation for the magnetic force exerted on an object moving by a current-carrying wire?

Answer 9

F_b=ILBsinӨ

• F_b= the magnetic force
• I= The current
• L= length of the wire field
• B= magnitude of the magnetic field
• Ө= the smallest angle between the velocity vector and the magnetic field.