Fields Flashcards
What is a force field?
a region in which a body experiences a non-contact force
How is a force field represented?
as a vector
How is a force field created?
interaction of mass/ static charge between moving charges
What are the similarities between electrostatic and gravitational forces?
Both have inverse-square force laws that have
many characteristics in common,
eg use of field lines, use of potential concept, equipotential surfaces etc
What are the differences between electrostatic and gravitational forces?
gravitational always attractive but electrostatic charges can repel
What is gravity?
Universal attractive force acting between all matter
How do you calculate the magnitude of the force between two point masses?
F = GMm/(r^2)
Newton’s law of gravitation
What is G?
the gravitational constant, 5.57 x10^-11
What is field strength?
the force applied by the field onto an object within the field
How does mass affect the force of gravity?
the larger the mass, the larger the force of attraction
What is a gravitational field line?
a line which indicates the direction of the gravitational force that would act on a test mass placed in the field
What is a test mass?
a mass small enough not to affect the shape of the field with its own gravity
What is the value of the Earth’s gravitational field strength, g
9.81
How is gravitational potential energy calculated?
V = -GM/r
Why is potential energy negative?
because work must be done to move towards infinity (against the force of attraction)
What is work done in a gravitational field?
the GPE gained, W=mΔV
What is a satellite?
something which orbits something else, eg moons, planets, stars etc
Which way does an electric field travel?
positive to negative
What is an electric field?
a region when a charged object will experience a force
What is meant by charge?
1C of charge is transported by 1A of current in 1second
What is static electricity?
a build up of electric charge on the surface of one object due to the removal or addition of electrons, usually caused by friction.
What does it mean if field lines are closer together?
the field is stronger
What is Coulomb’s law?
F = 1/4πε x QQ/r^2
Are gravitational fields radial or uniform?
radial as they only noticeably occur in large masses (eg planets). the closer you get to the surface the more uniform they appear
Are electric fields radial or uniform?
both
How does the force experienced by a charge in a uniform electric field change?
it doesn’t
How is electric potential calculated?
V = E/Q v = 1/4πε x Q/R
At which point from an electric field is there 0 potential energy?
infinity
At which point from a gravitational field is there 0 potential energy?
infinity
on a graph of gravitational field strength, g, against radius, r, what is given by the area under the graph?
Change in gravitational potential, ΔV
What is Kepler’s 3rd Law?
T^2 ∝ r^3
Define escape velocity.
the lowest velocity which a body must have in order to escape the gravitational attraction of a particular planet or other object
What is a geosynchronous orbit?
when an object is in a geosynchronous orbit around another, it appears to remain in a fixed point above one location on the surface. its orbit has the same time period as the planet in which it is orbiting, and so has a greater velocity as it must travel further (larger r from centre of earth than point on surface of earth)
On a graph of E against r, what does the area under the curve represent?
ΔV
