Gravitational And Electic Fields Flashcards
Define force field
A region in which a body experiences a non contact force
Define gravitational force
A region in which a body with mass experiences a non contact force
Is a force field a vector or scalar quantity?
Vector
What is the inverse square law in relation to gravitational field lines
No of field lines in a given area is inversely proportional to the distance squared
What is Newton’s law of gravitation?
The force between 2 masses is proportional to the product of their masses and inversely proportional to the distance between them squared
Define gravitational field strength
What is the unit?
Is it scalar or vector?
Force per unit mass
Nkm-1
Vector
What is the equation for potential energy
In a uniform field?
In a radial field?
Ep = mg x change in h
Ep = - G m1 m2
———-
r
Define gravitational potential
What is the unit?
Is it scalar or vector?
The work done per unit mass in moving a body from infinity to that particular point in a gravitational field
Jkg-1
Scalar
Gravitational potential difference
The energy needed to move a unit mass between 2 points in a gravitational field
What is a line of equipotential?
A line that joins all points where V is constant
Why is gravitational potential negative?
V or Ep is taken as zero
Because work is done (per unit mass if it is V)
By the mass to move it from infinity to that particular point
What is the centripetal force acting on a satellite?
Gravitational force
Define orbital time period
The time taken for a satellite to make one orbit
Describe a circular orbit
What affect does it have on energy?
Speed and distance above mass is constant
Total energy is constant
No energy change
Describe an elliptical orbit
What affect does it have on energy?
As speed increases, radius decreases
Kinetic energy increases as potential energy decreases
Total energy is constant
Define escape velocity
The speed at which an unpowered satellite must be traveling at to escape the gravitational field of a planet
Synchronous orbit
Orbiting object has an orbital period that is equal to the rotational period of the planet
Describe a geostationary satellite
5 points
It's orbit is in plane of the equator Time period = 24 hours Same fixed position relative to surface of the earth Orbital radius = 42 000 km Equatorial orbit
Define low orbiting
What is a low orbiting satellite used for?
A satellite which orbits between 180-2000 km above earth
Used for imaging and weather monitoring
What are the advantages and disadvantages of a low orbiting satellite?
Advantages
- cheaper
- less powerful transmitter required because it has a small orbital radius which is useful for communications
Disadvantages
- high orbital speed and proximity so multiple satellites are required to maintain constant coverage
Define electric field
A region in which a body with charge experiences a non- contact force
What is Coulomb’s law
The force between 2 point charges is proportional to the product of their charges and inversely proportional to the distance between them squared
Define electric field strength
What is the unit? (2 possibilities)
Force per unit charge
NC-1
Vm-1
What is the definition for potential energy in
Uniform electric fields?
Radial electric fields?
Ep = VQ
Ep = +- k Q1 Q2
———
r
