Fields part 1 Flashcards
What is a force field
An area in which an object experiences a non-contact force
2 ways to represent force fields
Vectors or diagrams containing field lines
What feature of field lines represent strength of force exerted
Distance between them
When are force fields formed
During interaction of masses, static charges or moving charges
When are gravitational fields formed
During interaction of masses
When are electric fields formed
During interaction of charges
3 similarities of gravitational and electric fields
Forces both follow an inverse-square law, use field lines to be represented, both have equipotential surfaces
2 differences of gravitational and electric fields
Gravitational fields only attractive, electric can be attractive or repulsive, electric field acts on charge, gravitational acts on mass
2 basic principles of gravity
Acts on any objects with mass, always attractive
Relationship between magnitude of gravitational force between 2 objects and the product of the masses of them
Directly proportional
Relationship between magnitude of gravitational force between 2 objects and the square of the distance between the 2 centre of masses
Inversely proportional
What is magnitude of gravitational force between 2 objects directly proportional to
Product of masses
What is magnitude of gravitational force between 2 objects inversely proportional to
Square of distance of 2 centres of masses
Force, gravitational constant, masses and distance formula
F = (Gm1m2)/r^2
F = (Gm1m2)/r^2 - what is G
Gravitational constant
F = (Gm1m2)/r^2 - what is m1 and m2
mass 1 and mass 2
F = (Gm1m2)/r^2 - what is r
Distance between centre of masses
F = (Gm1m2)/r^2 - what is F
Force
How many types of gravitational fields are there
2
What are the types of gravitational fields
Uniform, radial
Uniform field basic principle
Exerts same gravitational force on a mass everywhere in the field
Radial field basic principle
Gravitational force exerted depends on the position of the object in the field, further from centre means force decreases and vice versa
Why does the Earth’s gravitational field act uniform at the surface of the Earth
Area is so big that the lines appear in the same way as a uniform field (zoom in on a radial image and the lines look straight)
What is the gravitational field strength
Force per unit mass exerted by a gravitational field on an object
Gravitation field strength value in a uniform field vs radial
Constant in uniform, varies in radial
Gravitation field strength general formula
g = F / m
Gravitation field strength formula for radial fields only
g = GM / r^2
What is gravitational potential (V)
Work done per unit mass against gravitational force to move an object from infinity to a given point
What is the gravitational potential at infinity
0
Gravitational potential, negative or positive and why
Always negative, energy is released as gravitational potential is reduced
Gravitational potential formula for a radial field
V = - GM / r
V = - GM / r - what is G
Gravitational constant
V = - GM / r - what is M
Mass of object causing the field
Work done and gravitational potential difference formula
Work done = mΔv
Work done = mΔv - what is m
Mass of the object moved
What are equipotential surfaces
Surfaces created by joining points of equal potential together so potention on an equipotential surface is constant everyone
How much work is done when moving along an equipotential surface
None because constant gravitation potential means no potential difference when moving along the surface
Relationship between gravitational potential and distance between centre of 2 objects
Inversely proportional
What is the gravitational potential inversely proportional to
Distance between 2 centre of masses
Graph of gravitation potential against distance
Picture
How to measure gravitational field strength (g) on V-r graph
Negative gradient
Gravitational field strength, potential and distance formula
g = -ΔV/Δr
How to find gravitational potential difference from a gravitational field strength against distance graph
Area under the curve between those 2 points
What is Kepler’s 3rd law
Square of the orbital period (T) is directly proportional to the cube of the radius (r) T^2 = kr^3
Centripetal force formula
Centripetal force = mv^2 / r
What force acts as the centripetal force on an object orbiting a planet
Gravitational force
What is the total energy of an orbiting satellite
Kinetic energy + potential energy
What is the escape velocity of an object
Minimum velocity in order to escape gravitational field at the surface of a mass
What is an object’s escape velocity equal to
Magnitude of its gravitational potential energy
Escape velocity formula
square root of (2GM / r)
How does the mass of an object effect the escape velocity
It doesn’t
What is a synchronous orbit
Orbital period of satellite is equal to rotational period of the object that it is orbiting
Orbital period of a synchronous satelitte orbiting the Earth
24 hours
What are geostationary satellites
Follow geosynchronous orbit, orbital period is 24 hours, stay above same point on Earth as orbit directly above equator
What are geostationary satellites used for
Sending TV/phone signals
Why are geostationary satellites used for TV/phone signals
You don’t have to alter plane of aerial or transmitter as always at the same point above the Earth
What is the orbital radius of a geostationary satellite
4.2x10^7
What are low-orbit satellites
Satellites with lower orbits than geostationary satellites
Speed and orbital periods of low-orbit satellites compared to geostationary satellites
Travel much faster, smaller orbital periods
Benefits of low-orbital satellites
Require less powerful transmitters and can potentially orbit across the entire Earth’s surgace
What are low-orbit satellites used for
Monitoring the weather, making scientific observations about places which are unreachable, military applications
Low-orbit satellites as a use for communication
Good because they travel so quickly, many must work together to allow for constant coverage for a certain region
What does Couloumb’s law state
Magnitude of force between two point charges in a vacuum is directly proportional to the product of their charges and inversely proportional to the square of the distance between the charges
What is the squiggly e in terms of electric field
Permittivity of free space
Couloumb law formula
F = 1 / (4(pi)(squiggly e 0)) x ((Q1Q2) / r^2)
What is r in terms of the couloumb law formula
Distance between charges
When will the force in an electric field be positive or negative
Same sign then repulsive, different signs then attractive
Size of electrostatic forces compared to gravitational
Electrostatic force between subatomic particles is magnitudes greater than gravitational forces because the masses of subatomic particles are ver small whilst their charges are much larger
What is the electric field strength
Force per unit charge experienced by an object in an electric field
How does the electric field strength vary in a uniform vs radial electric field
Constant in uniform, varies in radial
Formula to find electric field strength in either a uniform or radial field
E = F / Q
Formula to find electric field strength in a uniform field
E = V / d
Formula to find electric field strength in a radial field
E = 1 / (4(pi)(squiggly e 0)) x (Q / r^2)
Which direction to electric fields flow
Positive to negative
What is the work done in an electric field
Work done by moving a charged particle between the parallel plates of a uniform field
What is the equation to find the work done by moving a charged particle between the parallel plates in a uniform field
Work done = Q / (change in V)
What happens when you fire a particle at right angles to a uniform electric field and how can you tell if it is charged / what charge is has
Charged particle will follow a parabolic shape, if charge is positive then it follows direction of field, if negative then moves opposite to direction of the field
What is absolute electric potential at a point
Potential energy per unit charge of a postive point charge at that point in a field
Where is the absolute magnitude of electric potential biggest
At the surface of a charge
Relationship between distance from charge and absolute electric potential
Bigger distance means a smaller absolute electric potential
At what point in a field is the absolute electric potential zero
Infinity
Absolute electric potential formula in a radial field
V = 1 / (4(pi)(squiggly e 0)) x (Q / r)
Is absolute electric potential negative or positive when the charge is positive
Positive
Is absolute electric potential negative or positive when the charge is negative
Negative
Gradient of a tangent to an electric potential against distance graph
Electric field strength
What is the electric potential difference
Energy needed to move a unit charge between two points
What is the work done in moving a charge across a potential difference equal to
Product of potential difference and charge
What is the work done in moving a charge across a potential difference formula
(change in)W = Q x (change in)V
Area under graph of electric field strength against distance
Electric potential difference
