1B Flashcards
Describe what a gravitational field is
A place where a mass experiences a force.
State what is meant by the term gravitational field strength.
Weight per unit mass
State what is meant by the term gravitational potential.
The gravitational potential (Vp) at a point in a field is the work done in bringing a unit mass
from infinity to the point. Vp = 0 at infinity.
Describe what is meant by a conservative field
In a conservative field the journey an object takes is not important, it is the starting and
finishing positions which determine physical values.
State what is meant by ‘escape velocity’.
The minimum velocity required to escape a gravitational field to infinity.
Describe what causes a star to become a black hole.
It contracts causing its escape velocity to increase to a value bigger than the speed of light
meaning not even light can escape.
State what the event horizon is.
The event horizon is the edge of a black hole
State what the Schwarzchild radius is.
The minimum radius required of a star for it to become a black hole.
Describe what happens to photons in gravitational fields
Photons are deflected by gravitational fields and objects can appear in different positions in
the sky because of this.
State how many dimensions there are in space-time
4 (x, y, z and time)
Describe what gravitational redshift is.
Photons emitted from stars lose energy as they escape from the star meaning they are
redshifted. (This is different from the redshift associated with stars moving away from us)
Describe what special relativity is.
Time dilates and length contracts when observing objects moving at speeds close to the
speed of light.
Describe what general relativity is.
Includes special relativity and Newtonian mechanics to describe gravity as a property of
space-time.
Describe the principle of covariance.
Space-time is curved due to the large masses in the universe. This curved space-time then
affects all photons and masses travelling through it.
With reference to general relativity explain why planets orbit stars.
Space-time is curved due to the star. Planets follow this curved space-time and orbit the
star.
State what is meant by non-inertial frames of reference.
Frames of reference that are accelerating with reference to an inertial frame of reference.
State what is meant by inertial frames of reference.
Frames of reference that are moving at a constant velocity relative to each other.
State the equivalence principle.
If a physics experiment is conducted in a reference frame accelerating at 9.8 ms-2 it would
yield the same results as if it were completed on the surface of the earth. It is impossible to
tell the difference between acceleration and the effects of gravity.
Two clocks are placed in 2 different gravitational fields. Clock A experiences a greater g than
clock B. Explain which clock runs more slowly.
Clock A would run more slowly as it experiences a greater gravitational field strength.
Explain why a star expands and contracts during its life cycle
Thermal pressure in the star is large and it overcomes the gravitational pull causing it to
expand. This expansion reduces the thermal pressure in the star meaning the gravitational
pull overcomes it and contracts the star. This cycle continues.
State what is released in a proton-proton chain reaction.
Positrons, neutrinos, Helium nucleus and energy.
State what is meant by the ‘brightness’ of a star.
Power per unit area emitted.
State what is meant by the ‘luminosity’ of a star.
Total rate at which energy is radiated by a star across all wavelengths
Describe what the ‘apparent brightness’ of a star is
The brightness of a star in the sky depends on 2 things; how bright the star is and how far
away it is. Apparent brightness takes account of how far away the star is so it can be
compared with other stars.
