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Title: GCSE Physics Exam 2
Description: These are concise, exam-focused notes made using the WJEC specification and BBC Bitesize. (I achieved an A*.) Topics are also sold separately.
Description: These are concise, exam-focused notes made using the WJEC specification and BBC Bitesize. (I achieved an A*.) Topics are also sold separately.
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2
...
The same change in momentum happens over a longer time so there is
decreased deceleration so the force decreases
...
2: Newton’s laws
Inertia
•
•
a resistance to a change in motion
directly proportional to mass and resultant force needed to change the motion
Newton’s first law of motion
•
An object will remain at rest or in uniform motion unless acted upon by an external resultant
force
...
Newton’s second law of motion
•
resultant force = mass × acceleration
Weight (in N)
•
•
Mass (in kg)
the force of gravity acting on an object
weight = mass × gravitational field strength
•
the amount of matter in an object
Gravitational field strength (in N/kg)
•
10 N/kg on Earth
Terminal (constant) speed
•
•
no resultant force
e
...
When a skydiver jumps, they fall faster, and air resistance or drag forces increase
...
When the drag forces become the same
as the weight or the thrust, then the forces become balanced
...
Newton’s third law of motion
•
If Body A exerts a force on Body B then Body B exerts an equal and opposite force on Body A
...
3: Work and energy
Energy
•
•
When a force acts on a moving body, energy is transferred although the total
amount of energy remains constant
...
Work
•
•
•
a measure of energy transfer
work = force × distance
work = energy transfer (in the absence of thermal transfer)
Kinetic energy
•
kinetic energy =
mass × velocity 2
2
; KE =
𝑚𝑣 2
2
Change in gravitational potential energy
•
gravitational potential energy = mass × gravitational field strength × change in height
; PE = 𝑚𝑔ℎ
Springs
•
force = spring constant × extension; 𝐹 = 𝑘𝑥
Force extension (𝐹-𝑥) graphs
•
area under graph = work done in stretching; 𝑊 =
4
𝐹𝑥
2
(in a linear relationship)
2
...
limited to situations involving a pivot and parallel forces (such as a balanced metre
rule)
Moments
•
•
•
the turning effects of a force around a fixed point (a pivot)
moment of force (in Nm) = force (in N) × perpendicular distance (in m);
𝑀 =𝐹×𝑑
e
...
a spanner being used to undo a nut
5
2
...
1 AU = 1
...
47 × 1015 m
speed of light = 3 × 107 m/s
The stability of stars
•
depends upon a balance between gravitational force and a combination of gas and
radiation pressure
Fusion
•
1
...
3
...
Stars generate their energy by the fusion of increasingly heavier elements
...
In main sequence, the forces acting on a star are balanced (gravitational inward
forces match outward gas and radiation pressure forces)
...
The star will begin to swell as the combination of gas and radiation pressure exceeds
the gravitational force and the forces become unbalanced
...
The origin of the solar system
•
•
•
from the collapse of a cloud of gas and dust
Gravitational forces cause the matter to get closer together creating the Sun and the
planets
...
7
The Hertzsprug-Russell (H-R) diagram
•
A means of displaying the properties of stars, depicting the evolutionary path of a
star
...
6: The Universe
Atomic absorption spectra
•
•
•
used to identify gases from a given absorption spectrum and additional data
Absorption lines arise from gas atoms in a star’s atmosphere absorbing wavelengths
of visible light that are specific to the elements present in a star
used by scientists in the nineteenth century to reveal the chemical composition of
stars
Cosmological red shift
•
•
•
•
•
•
revealed initially by Edwin Hubble’s measurements on the spectra of distant galaxies
revealed that the wavelengths of the absorption lines are increased and that this
effect increases with distance
attributed to the increasing space between the distant source and observers on
Earth (as opposed to Doppler red shift)
The recession velocity increases with the distance of the galaxy and it is this that
implies that all galaxies originated from a single point
...
supports the Big Bang model of the origin of the Universe, as if expansion of the
Universe is reversed, then everything would revert to one single point
...
This increase in wavelength is believed to be due to the
expansion of space
...
7: Types of radiation
Nucleon number
•
•
𝐴
the number of protons and neutrons in an atomic nucleus
Proton number
•
•
𝑍
the number of protons in an atomic nucleus
Isotopes
•
elements that have equal numbers of protons but differing numbers of neutrons in
their nuclei
Radioactive emissions
•
arise from unstable atomic nuclei because of an imbalance between the numbers of
protons and neutrons
Waste materials from nuclear power stations and nuclear medicine
•
•
•
radioactive
(some) will remain radioactive for thousands of years, due to long half-lives
require safe disposal, but only time can reduce the radiation emitted, so waste must
be stored
Methods of storage/disposal of nuclear waste
•
•
•
low-level radioactivity: in drums surrounded by concrete; in clay-lined landfill sites
intermediate-level radioactivity: mixed with concrete and put in a stainless-steel
drum in a purpose-built store
high-level radioactivity: underwater in large pools for 20 years, then placed in
storage casks in purpose-built underground stored where air can circulate to remove
the heat produced
10
Radioactive decay
•
•
random
has consequences when undertaking experimental work, requiring repeat readings
to be made or measurements over a lengthy period as appropriate
Alpha (α) radiation
•
•
•
•
4
2+
2He
or 42𝛼
helium nuclei (groups of two neutrons and two protons)
has a high ionising power (very damaging inside the body)
can penetrate air until skin
Beta (β) radiation
•
•
•
•
0
−1e
or −10β
high-energy electrons
has a medium ionising power
can penetrate air and skin until aluminium
Gamma (ɣ) radiation
•
•
•
•
ɣ
electromagnetic
has a low ionising power (easily passes through the body)
can penetrate air, skin and aluminium until lead
Background radiation
•
•
has natural sources (such as cosmic rays, rocks and soils and living things) and
artificial sources (such as medical X-rays, nuclear missiles and nuclear power)
varies with altitude as at higher altitudes there is more cosmic radiation
Radon
•
•
originates from rocks (especially granite), so the type of rock in an area determines
the amount of radon
can be avoided by improving ventilation by opening windows, fitting air bricks and
installing a fan underneath the house
11
2
...
Uses of radioactive materials
•
•
•
smoke alarms using alpha radiation (long half-life; weak penetration so smoke can
break small current in the air)
measuring the thickness of paper using beta radiation (long half-life; medium
penetration)
external cancer treatment using gamma radiation (long half-life; strong penetration)
12
2
...
g
...
( 226
88Ra → 86Rn + 2He)
29
29
e
...
Aluminium decays by releasing a beta particle to form silicon
Title: GCSE Physics Exam 2
Description: These are concise, exam-focused notes made using the WJEC specification and BBC Bitesize. (I achieved an A*.) Topics are also sold separately.
Description: These are concise, exam-focused notes made using the WJEC specification and BBC Bitesize. (I achieved an A*.) Topics are also sold separately.