Unit 12 Variables - AP Physics C

F||

component of force parallel to motion: this component does work/changes the speed, but can’t change the direction; N

F⊥

component of force perpendicular to motion: this component changes the direction but can’t do work/change the speed; N

W

Work: change in a system’s energy. Only caused by parallel force components; J

E

electric field; N/C

FE

Electric force. Always parallel or anti-parallel to the electric field. Can do work; N

FB

Magnetic force. Always perpendicular to velocity and the magnetic field. Can’t

do work; N

I

Current: flow of objects with charge; A or C/s

B

Magnetic field; T

l (magnetism)

Length of current; m

0 (magnetism)

Angle between charge motion and magnetic field; o

n (magnetism)

Ratio of turns/meter for a solenoid: n =turns/length

μ0 (magnetism)

Vacuum permeability; 4π x 10^-7 (T*m)/A

r (magnetism)

Distance between current and spot; m

J (circuits)

Current Density ≡ dI/dA = current/(cross − sectional area); A/m²

dA in terms of dr

Step 1: do d/dr (Area formula) Step 2: solve for dA; dAcircle=2πr dr

Cross-Sectional Area

Area of a hollow cylinder = π(b²-a²)

Magnetic Force on a Current-Carrying Wire:

FB = ∫ I dl*B = ILBsinθ

Magnetic Force on a Moving Charge:

FB = q(v × B) = qvBsinθ

Magnetic Field a distance r from a Straight Wire:

B =μ0I/2πr

Magnetic Field in the center of a solenoid:

B = μ0nI = μ0(N/L)I