Okay, so this is driving me absolutely nuts. I have really good memorization skills but I cant seem to keep the electric field, electric potential, coulombs law, and voltage formulas straight (the ones that use some variation of "something=k*one or two Qs/r or r^2") . If there is no mnemonic for these formulas, can someone show me how to derive them? If I need to clarify what Im asking please let me know
Electric Field Mnemonic
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So, a good one to remember is that Force=Coulomb's Law=k(q)(q)/r^2
And the force on a charge q is: F=qE
so if you have charges q and Q, the force is the charge q x the electric field created by Q:
F=qE so that means that E=kQ/r^2
As for electric potential, just remember that its formula is the same as electric field except that the denominator is r instead of r^2. so potential=kQ/r
And the force on a charge q is: F=qE
so if you have charges q and Q, the force is the charge q x the electric field created by Q:
F=qE so that means that E=kQ/r^2
As for electric potential, just remember that its formula is the same as electric field except that the denominator is r instead of r^2. so potential=kQ/r
Vector quantities (electric force and electric field), r^2 at the bottom.
Scalar quantity, just r at the bottom.
Only scalar quantity is electric potential. Force and field are vector quantities.
potential and field is relative to only 1 charge, while force is acting between 2 charges.
KQq/(r^2) = Force (measured in N)
KQ/(r^2) = electric field (E)
Kq/r = electric potential (V)
As far as relatioinships go,
Force is just qE.
Potential energy is just qV.
Scalar quantity, just r at the bottom.
Only scalar quantity is electric potential. Force and field are vector quantities.
potential and field is relative to only 1 charge, while force is acting between 2 charges.
KQq/(r^2) = Force (measured in N)
KQ/(r^2) = electric field (E)
Kq/r = electric potential (V)
As far as relatioinships go,
Force is just qE.
Potential energy is just qV.
Relate them to the gravitational force equation if you already know it
If you know F=Gm1m2/r^2, then just replace G with K, and m with q.
So g (gravational constant) is like E (electric field) and since F=mg, again replace m with q and g with E and you get F=Eq
W=mgd
W=Eqd=voltage=potential energy
Gravity and electricity have very similar equations, except gravity is intuitive, at least more than electricity, so try to relate the two if thats helpful.
If you know F=Gm1m2/r^2, then just replace G with K, and m with q.
So g (gravational constant) is like E (electric field) and since F=mg, again replace m with q and g with E and you get F=Eq
W=mgd
W=Eqd=voltage=potential energy
Gravity and electricity have very similar equations, except gravity is intuitive, at least more than electricity, so try to relate the two if thats helpful.
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Just remember this one to start with:
Fe = k (q*Q)/r^2
Now, remember that W = F*d, so if you multiply both sides by the distance r, you get:
Fe * r = W = EPE (electric potential energy) = k(q*Q)/r
Next, recall that EPE / q = V (voltage). So, divide both sides of the Fe equation by the charge q:
EPE / q = V = k (Q)/r
Lastly, remember that E (electric field) = V / d (because E has the units volts/meter). Take the voltage equation just derived and divide both sides by the distance r:
V / r = E = k (Q)/r^2
Here is a summary table:
Fe = k (q*Q)/r^2
Now, remember that W = F*d, so if you multiply both sides by the distance r, you get:
Fe * r = W = EPE (electric potential energy) = k(q*Q)/r
Next, recall that EPE / q = V (voltage). So, divide both sides of the Fe equation by the charge q:
EPE / q = V = k (Q)/r
Lastly, remember that E (electric field) = V / d (because E has the units volts/meter). Take the voltage equation just derived and divide both sides by the distance r:
V / r = E = k (Q)/r^2
Here is a summary table:
