Gravitational and Electric Fields Flashcards
What do field lines show?
The direction of force on a mass (gravitational) or positive charge (electric) placed in the field.
State Newton’s Law of Gravitation/ Coulomb’s Law (use F = GMm/r² or F=kQq/r²)
The force between two objects is proportional to the product of their masses/ charges and inversely proportional to the square of their separation.
Define potential.
The work required to move a unit mass/ positive charge from infinity to that point in the field.
What do equipotentials show?
The potential at certain intervals around a planet/ charge. No work is needed to move along equipotentials.
State Kepler’s 3rd law.
T² ∝ r³
What is a Geostationary orbit?
- Time period = 24 hours.
- Orbits above same point (on equator).
- Must all be the same height according to Kepler’s Law.
- Used for communication, GPS, internet, television
What is a low polar orbit?
- Lower radius = shorter time period.
- Moves from pole to pole: able to survey whole Earth.
- Used for surveillance and weather.
What is escape velocity, and how is it calculated?
- The minimum speed any object needs to be launched with in order to escape a planet’s gravitational field.
- GMm/r = 1/2 mv²
What is distance of closest approach, and how is it calculated?
- The minimum distance a charge can get to a like charge before turning around.
- kQq/r = 1/2 mv²
State the characteristics of a uniform field.
- p.d. set up across two parallel plates
- Field lines are parallel and equipotentials are equally spaced.
- Field strength and force are same everywhere in field.
What will the trajectory of a charged particle at right angles to a uniform field be?
Parabolic (suvat)
If a charged particle is levitating in a uniform field, what must be true?
Forge due to electric field must equal its weight.
