Physics Paper 1 Definitions

Define simple harmonic motion of an object

Acceleration is directly proportional to displacement from the equilibrium position and is directed towards the equilibrium position

State and explain how stellar parallax is used to measure distances in space

Stellar parallax is the apparent displacement of a star relative to the position of more distant stars, it is caused by the Earth’s orbit around the Sun. An angle of parallax of 1 arcsecond when displacement of Earth is 1AU corresponds to a distance of 1 parsec

State the key assumptions made in the kinetic theory of gases

• Forces between particles are negligible except during collisions

• Collisions are perfectly elastic

• Time of a collision is negligible compared to the time between collisions

• Particles occupy negligible volume

• Large number of molecules are in random motion

Explain the term centripetal force

Resultant force that acts perpendicularly to the direction of motion

State Hubble’s Law

Recessional velocity of a galaxy is directly proportional to its distance from us

Suggest why hydrogen spectral lines play an important role in determining red shift of galaxies

Relative abundance of hydrogen

Define internal energy of a substance

The sum of the kinetic and potential energies of its molecules

Explain what is meant by the term homogeneous

Uniform distribution of matter

State the characteristics of a black hole

• Infinitely dense

• Has an escape velocity greater than the speed of light

Describe the evolution of the Universe up to the formation of the first nuclei

1. At the Big Bang, the Universe is a singularity

2. Expansion/inflation of high energy photons, but no matter

3. Quarks and leptons form

4. Quarks combine to form hadrons

5. Hadrons combine to make nuclei

Describe the doppler effect

Observed frequency is different to source frequency when source moves relative to the observer

Define gravitational potential

Work done per unit mass to move an object from infinity to that point

Define gravitational potential energy

Work done in moving an object from infinity to that point

Describe the origin of microwave background radiation

• During the Big Bang, and the universe expanded

State Newton’s second law of motion

Net force is directly proportional to the rate of change of momentum

Describe the formation of a neutron star

• remnant of a red supergiant star

• formed by gravitational collapse of core, star undergoes a supernova

Give the characteristics of a neutron star

• extremely dense

• has a very strong gravitational field

• supported by neutron degeneracy pressure

• fusion is no longer taking place

• core has mass greater than Chandrasekhar limit