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Question 1

Describe what a gravitational field is

Answer 1

A place where a mass experiences a force.

Question 2

State what is meant by the term gravitational field strength.

Answer 2

Weight per unit mass

Question 3

State what is meant by the term gravitational potential.

Answer 3

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.

Question 4

Describe what is meant by a conservative field

Answer 4

In a conservative field the journey an object takes is not important, it is the starting and
finishing positions which determine physical values.

Question 5

State what is meant by ‘escape velocity’.

Answer 5

The minimum velocity required to escape a gravitational field to infinity.

Question 6

Describe what causes a star to become a black hole.

Answer 6

It contracts causing its escape velocity to increase to a value bigger than the speed of light
meaning not even light can escape.

Question 7

State what the event horizon is.

Answer 7

The event horizon is the edge of a black hole

Question 8

State what the Schwarzchild radius is.

Answer 8

The minimum radius required of a star for it to become a black hole.

Question 9

Describe what happens to photons in gravitational fields

Answer 9

Photons are deflected by gravitational fields and objects can appear in different positions in
the sky because of this.

Question 10

State how many dimensions there are in space-time

Answer 10

4 (x, y, z and time)

Question 11

Describe what gravitational redshift is.

Answer 11

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)

Question 12

Describe what special relativity is.

Answer 12

Time dilates and length contracts when observing objects moving at speeds close to the
speed of light.

Question 13

Describe what general relativity is.

Answer 13

Includes special relativity and Newtonian mechanics to describe gravity as a property of
space-time.

Question 14

Describe the principle of covariance.

Answer 14

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.

Question 15

With reference to general relativity explain why planets orbit stars.

Answer 15

Space-time is curved due to the star. Planets follow this curved space-time and orbit the
star.

Question 16

State what is meant by non-inertial frames of reference.

Answer 16

Frames of reference that are accelerating with reference to an inertial frame of reference.

Question 17

State what is meant by inertial frames of reference.

Answer 17

Frames of reference that are moving at a constant velocity relative to each other.

Question 18

State the equivalence principle.

Answer 18

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.

Question 19

Two clocks are placed in 2 different gravitational fields. Clock A experiences a greater g than
clock B. Explain which clock runs more slowly.

Answer 19

Clock A would run more slowly as it experiences a greater gravitational field strength.

Question 20

Explain why a star expands and contracts during its life cycle

Answer 20

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.

Question 21

State what is released in a proton-proton chain reaction.

Answer 21

Positrons, neutrinos, Helium nucleus and energy.

Question 22

State what is meant by the ‘brightness’ of a star.

Answer 22

Power per unit area emitted.

Question 23

State what is meant by the ‘luminosity’ of a star.

Answer 23

Total rate at which energy is radiated by a star across all wavelengths

Question 24

Describe what the ‘apparent brightness’ of a star is

Answer 24

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.

Question 25

State what ‘absolute magnitude’ is

Answer 25

The brightness of a star measured at a set distance from the star (32.6 light years).

Question 26

State what ‘apparent magnitude’ is

Answer 26

The brightness of a star measured from Earth.

Question 27

Describe what a sunspot is

Answer 27

A dark region where cooler plasma sinks back into the sun.

Question 28

Describe what a solar flare is.

Answer 28

An emission of X-rays from the sun.

Question 29

State what type of star is found in the bottom left hand corner of a Hertzsprung-Russell
diagram

Answer 29

White dwarf.

Question 30

State what type of star is found in the top right hand corner of a Hertzsprung-Russell
diagram.

Answer 30

Red giant.

Question 31

State what the region from the top left to the bottom right of a Hertzsprung-Russell diagram
is known as.

Answer 31

The main sequence where stars spend a large portion of their life cycle expanding and
contracting.