Fields Flashcards
electrostatic field
- field strength (E) units are NC^–1
- created by charged object
- experienced by charged objects in the field
- two type of charge, negative (due to a surplus of electrons) and positive (due to a deficit of electrons)
- can be attractive (unlike charges) or repulsive (like charges)
“the force per unit charge experienced by a small positive test charge placed in the field”
where does the charge exist for a spherical object?
only on the surface of the object. there is no electrostatic field within the object
gravitational potential energy
work done in moving it from infinity to that point
unit = J
gravitational potential
the work done in taking a unit mass from infinity to that point
equipotential lines
they are drawn at 90º to the field lines
Vesc definition
the speed a body needs to escape the gravitational attraction of a planet from the surface of the planet
derive Vesc
for a body of mass m to escape it must reach an infinite distance away where Ep=0
it must gain GMm/r of energy, which is provided in the form of kinetic energy
so 1/2m(Vesc)^2 = GMm/r
rearrange for Vesc
––> Vesc = √(2GM/r)
(so it is independent of the body’s mass)
Vorbit =
= √(GM/r) = √(–Vg)
how to find orbital period of an object undergoing orbital motion
- Find Vorbit
- Find distance (orbit)
- Find period
derive the formula for the total energy of an object undergoing orbital motion
Ek=1/2 mv^2 but v=√(GM/r) ––> Ek=1/2 GMm/r
and Ep=–GMm/r
so Et=Ek+Ep ––> = –1/2 GMm/r = (Vg m)/2
total energy of object undergoing orbital motion graph
Ek goes from +ve to close to 0
Et goes from –ve to close to 0
Ep goes from –2Ek to close to 0
electric potential at a point in an electric field
work done per unit charge in bringing a small positive test charge from infinity to that point
