Section 9 - Gravitational and Electric Fields Flashcards
Is the force in a field contact or non-contanct?
Non-contact
Is force a vector or scalar quantity?
Vector
What are the similarities between electrostatic and gravitational forces?
- Inverse square force laws
- Potential concept
- Equipotential surfaces
- Use of field lines
What are some differences between electrostatic and gravitational forces?
The gravitational forces from masses always attract, whilst charges may repel or attract
What is gravity?
The universal attractive force which acts between all matter
What is G?
The universal gravitational constant
What is Newton’s law of gravitation?
Force between 2 objects is proportional to the product of their masses/charges and inverseley proportional to the square of their seperation
What can field lines tell you about a field?
The direction of the field and the strength of the field depending on the density of the field lines
What is g?
- The force per unit mass in a uniform field
- In a radial field the magnitude of g is the proportionality constant at that point between force and mass
What is gravitational potential?
The work done/energy required in bringing 1 kg/unit mass from infinity to the point
What is the gravitational potential difference?
Gravitational potential difference is the difference in the gravitational potentials of 2 points in a gravitational field
What is an equipotential surface?
A surface in which every point on the surface has the same potential
How much work is done when you move 1km in any direction on an equipotential?
No work is done when moving across equipotentials, as the potential at each point is the same
Why is gravitational potential a negative value?
Work needs to be done to move an object from the inside of the field to the outside of the field
SInce outside the field’s potential is defined as 0 then the potential inside the field must be negative
How is the orbital period related to the radius of a circular orbit?
T^2 ∝ R^3
What equations could you use to find the speed of an orbiting satellite?
The orbiting object (mass m) is in circular motion, so we would use F = ma with F = GMm/r^2 rearranged to a=v^2 r=ω^2 x r.
This can be sold to find the speed (V0, angular speed (ω), the radius of the orbit or using T=2π/ω its period
Compare the PE and KE of a lower orbit to a higher one
A lower orbit has less potential energy and more kinetic energy than a higher orbit
What is the period of a geosynchronous orbit?
24 hours
When calculating the force between two particles, what can air be treated as?
A vacuum
For a charge sphere the charge can be assumed to be at what part of the sphere?
The centre
Which is stronger? The gravitational force of subatomic particles or the electrostatic force
The electrostatic force
Electric field line always go from ________ to ________.
Electric field lines go away from positive charge to negative charge
What is electric field strength?
The force per unit charge acting on a positive charge
What is electric potential energy?
The work done in bringng a unit charge from infinity to that point
