Physics Paper 2

P1, P2, P3, P4

P4) Isotope

P4) Isotope

Atoms of the same element with different numbers of neutrons

Some isotopes are radioactive

P4) Radioactive Decay

When an unstable nucleus becomes more stable over time by randomly (spontaneously) emitting ionising radiation

P4) Activity

The rate at which a source of unstable nuclei decay

Becquerel (Bq) = 1 decay per second

P4) Count-rate

The number of decays recorded each second by detector

P4) What is alpha radiation (α)?

• 2 protons and 2 neutrons (same as a helium nucleus)

• Large particles

• Can travel around 5cm in air before they collide with air particles and stop

• Alpha particles are stopped by a single sheet of paper

• Very strongly ionising

P4) What is beta radiation?

• an electron which is ejected from the nucleus at very high speed

• A beta particle is formed inside the nucleus when a neutron changes into a proton and an electron

• Can travel around 15cm before stopping

• Beta particles can be stopped by a few millimetres of aluminium

• Quite strongly ionising

P4) What is gamma radiation?

• Electromagnetic radiation for the nucleus

• Gamma radiation travels several meters in air before stopping

• Gamma radiation is stopped by several centimetres of lead

• Weakly ionising

P4) Ionising power

When radiation collides with atoms, that can cause the atoms to lose electrons and form ions

P8) Moon

Moons are natural satellites which orbit planets

P8) How do stars form?

• Stars form from nebulas (clouds of dust and gas)

  • In a nebula the gas is mainly hydrogen

1. Gravity causes the cloud of dust and gas to collapse

2. The dust particles move faster, causing the temperature to rise to millions of degrees Celsius

   • This is called a protostar

3. When the temperature of the protostar gets hot enough, then hydrogen nuclei join together to form helium

   • This is nuclear fusion

4. Now the protostar has turned into a main-sequence star

• The force of gravity acting inwards is balanced by the force due to fusion energy acting outwards (equilibrium)

P8) What is the life cycle for a star the same size as our sun?

• Hydrogen nuclei fuse together to make larger nuclei such as helium

1. Hydrogen in the star begins to run out

2. This means the outward force due to fusion energy is less than the inward force due to gravity

3. This causes the star to collapse inwards which causes the temperature to increase

4. The helium nuclei fuse to form heavier elements

5. Star expands to form a red giant

6. Once the red giant stops fusing helium, it shrinks to form a white dwarf

7. The white dwarf no longer carries out any fusion so it gradually cools down

8. Eventually it stops releasing energy and becomes a black dwarf

P8) What is the life cycle for a star that is greater than our sun?

• Hydrogen nuclei fuse together to make larger nuclei such as helium

1. Hydrogen in the star begins to run out

2. This means the outward force due to fusion energy is less than the inward force due to gravity

3. This causes the star to collapse inwards which causes the temperature to increase

4. Once it runs out of hydrogen it expands into red super giants

5. The helium nuclei fuse to form heavier elements

6. Once the red super giant stops carrying out nuclear fusion it EXPLODES

   • This is a supernova (the temperature of a supernova is high enough to produce elements heavier than iron)

7. During the explosion, these elements are distributed throughout the universe

8. After the supernova, the remains can form one of two objects:

   • Neutron star- neutrons densely packed together

   • Black hole- has such a large gravity that not even light can escape

P8) Elements heavier than …. can only be produced in a supernova

Iron

P8) Absorption Spectra

• These wavelengths are emitted from the sun towards Earth

• However the suns atmosphere contains many different chemicals and some can absorb certain wavelengths of light

• When the light reaches Earth, wavelengths are missing

• This causes the physical dark lines

P8) Red Shift

• Light from distant galaxies have different absorption spectras

• The lines are in the same pattern but shifted towards the red end of the spectrum

• This happens as light waves get stretched on their way to Earth

• This proves that the space between us and the galaxy is expanding/stretching (imagine dotting two points on a balloon and blowing it up)

P8) The Big Bang Theory

• Proposes all the matter in the universe that originally occupied a tiny space (dense and hot)

• EXPLOSION

• Then space itself started to expand continuing to today

P8) Orbit

The curved path of one celestial object or spacecraft around another celestial object

P8) What results in a steady orbit?

• Instantaneous velocity of the orbiting object (the direction is always changing so the satellite is always accelerating)

• Strong gravitational pull of the larger object that its orbiting

P8) Describe the relationship between the size of an object’s orbit and its speed

The smaller an object’s orbit —> The faster the object must be travelling