AP Electricity and Magnetism Equations to memorize Flashcards
Rotational instantaneous power
P = τ·ω
Electric field of a point charge
E = kq / r2
Ampere’s law
μ0I = ∫(B)(ds)
Integral of a differential
∫ dx = x + C
Centripetal acceleration based upon v
ac = v2 / r
Lenz’s law
The current induced by a changing magnetic flux creates a field which opposes the change
Energy in an inductor
Newton’s third law
Fab = -Fba
Impulse for a constant force
J = (ΣF)(Δt)
(Impulse = force x time)
Area under a force/time function
Impulse
Instantaneous power
P = F∙v
Energy in a capacitor (3)
U = ½QV = ½CV2 = ½Q2/C
Derivative chain rule
d/dx (u) = (du / dv)(dv / dx)
Resistors in series
Rseries = R1 + R2 + R3 ….
Spring force
Fsp = -ks
Derivative quotient rule
d/dx (u / v) = (1/v)(du/dx) – (u/v2)(dv/dx)
Relative motion
va,c = va,b + vb,c
Center of mass
rcm = (m1)(r1) + (m2)(r2) … / Σm
Rule for the angle of the cross product
Rotate counterclockwise from the first vector to the second vector
Conservation of angular momentum
I1ω1 = I2ω2
Centripetal acceleration based upon ω
ac = ω2R
Relationship between the force and the change in energy per unit distance.
F = -dU/ds
This is a combination W = f x d and W = -ΔU
Work – potential energy relationship
-W = ΔU
Resistance of a wire
R = ρ(L/A)
Where ρ is resisitivity
L = length
A = cross sectional area
Magnetic field of a straight wire
B = μ0I / 2πR
vf2 equation
vf2 = vi2 + 2(a)(Δs)
Force down an incline
Fll = Fg ∙ sinθ
Gravitational potential energy on a planet
Ug = mgh
Rotational inertia of point masses
I = Σ(mr2)
Slope of a velocity/time graph
Acceleration
Torque (2)
τ = F∙ r┴
( torque = force times “lever arm” )
(The lever arm is just the shortest distance between the axis of rotation and the path the force is acting along.)
Cartesian to polar coordinates (2)
v = √(vx2 + vy2)
Rotational work
Wrot = (τ)(Δθ)
Integral of an exponential term
∫ (eu)dx = (1/u’)(eu) + C
Describe the electric field inside a conductor
Electric charge and field are zero
Voltage across an inductor
V = -L(dI / dt)
Battery emf
EMF = V - IRint
Magnetic flux
ФB = A∙B = ABcosθ
(Often, in the problems we do, the area vector and the magnetic field will be parallel, so the cosθ is equal to one and thus dropped from the equation.)
Resistors in parallel
1/Rparallel = 1/R1 + 1/R2 + 1/R3….
Centripetal force
Fc = mac
Period of a simple pendulum
T = 2π√(L/g)
Kinetic friction
Fkf = ± μkf∙ FN
Integrating with a constant
∫ k f(x)dx = k ∫ f(x)dx
Period of a physical pendulum
T = 2π√(I/mgd)
Power in a circuit (3)
P = IΔV
Electric potential (general)
V = U / q
Displacement under constant acceleration
Δs = (vi)(Δt) + ½(a)(Δt2)
Electrostatic force between point charges
FE = kq1q2 / r2
Acceleration due to gravity
g = G∙mp/rp2
(This is pretty much just the Law of Universal Gravitation with the mass of the planet and the radius of the planet plugged in.)
RC circuit growth
Vc = Vs(1e-t / RC)
RC the time constant (tau) (resistance x capacitance)
Vs is the supplied voltage
Law of Biot-Savart
Gravitational potential energy in space
Ug = (-G∙m1∙m2)/ r
Universal force of gravity
Fg = (G∙m1∙m2 )/ r2