Download Physics p1 revision 2017 PPTX

Physics
P1 revision
Past paper question
solid
gas
solid
Past paper question
1. The marbles model act as molecules / atoms
2. Molecules leaving a liquid = evaporation OR
marbles leaving tray = evaporation
Past paper question
1. To evaporate the alcohol requires
energy
2. This energy (heat) is taken from the
skin and the skin feels cold
Heat Energy
Transfer
Conduction – key facts
1.
2.
3.
4.
Metals are good conductors
Non-metals and gases are poor conductors
Insulators are poor conductors
Free electrons are able to move about in metals
and the part of the metal atoms that are left behind
are charged metal ions
5. These metal ions are packed closely together and
vibrate all the time
6. The hotter the metal, the faster the vibrations of the
ions
7. This kinetic energy is then transferred from the
hotter parts of the metal to the cooler parts of the
metal by the free electrons as they collide with the
ions as they move about
Convection – key facts
1. Liquids and gases are fluids
2. When fluids are heated, they expand as the particles
move faster and further apart
3. The liquid or gas then becomes less dense as the
particles take up more space but the particles are still
the same size
4. The liquid or gas in hot areas is less dense than the
liquid or gas in cold areas, so it rises into the cold
areas.
5. The denser cold liquid or gas falls into the warm areas.
6. This cycle continues until the heat source is removed
7. The wind is caused by convection currents from the
Earth being heated by the sun
Emitting IR radiation
All objects emit (give out) some thermal radiation, hotter object
give out more IR. The greater the temperature difference the
greater the rate of transfer.
Certain surfaces are better at emitting (giving out) IR radiation
than others. The greater the surface area the greater the rate of
transfer.
worst emitter
best emitter
matt
black
white
silver
Matt black surfaces are the best emitters and absorbers of radiation.
Shiny surfaces are the worst emitters and absorbers of radiation.
Evaporation – key facts
1. The particles in a liquid have different amounts
of kinetic energy.
2. Some will have enough energy to escape from
the liquid at the surface and become a gas.
3. The remaining particles in the liquid have a
lower average kinetic energy than before, so
the liquid cools down as evaporation happens.
4. This is why sweating cools you down.
5. The sweat absorbs energy from your skin so
that it can continue to evaporate.
Condensation – key facts
1. The particles in a gas have amounts of kinetic
energy. Some may not have enough energy to
remain as separate particles, particularly if the
gas is cooled down.
.
Factors affecting condensation
and evaporation – key facts
1. Condensation happens faster if the
temperature of the gas is lowered
2. Evaporation happens faster if the
temperature of the liquid is increased.
3. Evaporation happens faster if the surface
area is increased
4. Evaporation happens faster if air is moving
over the surface of the liquid
U Values
High U value = bad insulator
Low U value = good insulator
Single glazed window
Double glazed window
Brick wall
Insulated brick wall
2.0
1.5
1.2
0.3
Payback time
Payback time is the time to ‘get your money back’.
payback time (in years) =
cost of insulation
saving each year
Example:
Adding silver reflectors behind radiators
costs £25 and saves £50 per year.
payback time = 25
50
= 0.5 years
= 6 months
Energy changes
To describe an energy change for a
light bulb we need to do 3 steps:
1) Write down
the starting
energy:
2) Draw an arrow
Electricity
3) Write down
what energy types
are given out:
Light + Heat
Energy efficiency
Most Kids Hate Learning GCSE Energy Names
•
•
•
•
•
•
•
•
•
•
Magnetic
Kinetic (movement energy)
Heat (thermal energy)
Light
Gravitational potential
Chemical
Sound
Electrical
Elastic potential
Nuclear
Energy efficiency
Wasted
Input
Useful
Energy efficiency
Wasted
Input
Useful
Energy efficiency
Wasted
Input
Useful
Sankey Diagram
The thickness of each arrow is drawn to
scale to show the amount of energy
Efficiency
Efficiency is defined as
Efficiency (%) = useful energy output x 100
total energy input
• The closer the efficiency is to 1 or 100%, the
more efficient the device is and the less
energy it wastes
• No device will have an efficiency of 1 or
100% as some energy is always lost as heat
and warms up the surroundings
Past paper question
1. 120 / 200 =
2. 0.6 or 60%
1. Most energy out as light or least energy wasted as heat
6 squares
20 squares
14 squares
1. Useful / input
2. 6 / 20 = 0.3 or 30%
What is specific heat capacity?
The specific heat capacity of a material is the amount of
energy required to raise 1 kg of the material by 1 °C.
It can be used to work out how much energy is needed to
raise the temperature of a material by a certain amount:
specific heat
temperature
energy = mass ×
×
capacity
change
E
=
m x
c
x
θ
 Energy is measured in joules (J).
 Mass is measured in kilograms (kg).
 Temperature change is measured in °C.
 Specific heat capacity is measured in J/kg°C.
Non-Renewable energy
All of these methods are used to heat water to create
steam which is used to turn the turbine and generate
electricity
Energy source
Coal
Advantages
Disadvantages
Relatively cheap to mine, Non-renewable,
ready made fuels
burning produces CO2
Oil
Short start-up time,
ready made fuels
Gas
Slightly cleaner fuel than oil Non-renewable,
and gas and is a ready
burning produces CO2
made fuel
Nuclear power
Produces lots of energy,
does not produce CO2
Non-renewable,
burning produces CO2
Non-renewable,
produces dangerous
nuclear waste
Renewable energy
1. Wind, hydroelectricity and geothermal all turn a
turbine which will create electricity
2. Solar cells use light to create electricity
Energy source
Advantages
Disadvantages
Wind
Renewable, no fuel
costs
No wind sometimes
(unreliable), noisy
Hydroelectric
Renewable, no fuel
costs
Can flood areas,
disrupts habitats
Solar
Renewable, no fuel
costs
No sun at night, some
countries don’t get
enough sun in the day
Geothermal
Renewable, no fuel
costs
Only available in
volcanic regions,
Transformers and the supply chain
Boiler
Generator
Cost of electricity
•
•
•
•
•
E=P×t
E - energy transferred in kWh
P - power in kW
t - time in h.
Power is sometimes given in W. To
convert from W to kW you must divide by
1,000.
• E.g. 2,000 W = 2,000 ÷ 1,000 = 2 kW.
1.
2.
3.
4.
Energy = power × time
Power = 0.85 kW, time = 0.1
Energy = 0.085
kWh
• Electricity meters measure the number of units of
electricity used. The more units used, the greater the
cost.
total cost = number of units × cost per unit
• E.g. if 5 units of electricity are used at a cost of 8p
per unit, the total cost will be
5 × 8 = 40p
• The number of units used can be calculated using
this equation:
total cost = power (kW) × time (h) × cost per unit
P1b Waves
• Waves are vibrations that transfer energy
from place to place without matter (solid,
liquid or gas) being transferred.
• Some waves must travel through a
substance. The substance is known as the
medium and it can be solid, liquid or gas.
TRANSVERSE waves
• In transverse waves, the oscillations
(vibrations) are at right angles to the
direction of travel and energy transfer
• Light and other types of electromagnetic
radiation are transverse waves. All types of
electromagnetic waves travel at the same
speed through a vacuum, such as through
space.
Longitudinal waves
• In longitudinal waves, the oscillations are
along the same direction as the direction of
travel and energy transfer.
• Sound waves and waves in a stretched
spring are longitudinal waves.
• Mechanical Waves (like a slinky spring) can
be either transverse or longitudinal.
Labelling waves
• The wavelength of a wave is the distance
between a point on one wave and the same
point on the next wave.
• The frequency of a wave is the number of
waves produced by a source each second. It
is also the number of waves that pass a
certain point each second. Measured in Hz
Wave equation
• The speed of a wave is related to its
frequency and wavelength, according to this
equation:
v=f×λ
• v is the wave speed in metres per second,
m/s
• f is the frequency in hertz, Hz
• λ (lambda) is the wavelength in metres, m.
Past paper question
1. speed = frequency × wavelength
1. 300, 000,000 / 909 000
2. = 330m
A
W
W
1. 0.1m X 2Hz
2. 0.2m/s
reflection
The angle of incidence equals the angle of reflection
• Sound waves and light waves reflect from surfaces.
• Smooth surfaces produce strong echoes when sound
waves hit them, and they can act as mirrors when
light waves hit them. The waves are reflected
uniformly and light can form images
object
image
1. Virtual
2. Upright
3. Laterally
inverted
refraction
• Sound waves and light waves change speed when
they pass across substances with different densities.
• This causes them to change direction and this effect
is called refraction.
• Refraction doesn't happen if the waves cross the
boundary at an angle of 90°(the normal) - they carry
straight on.
diffraction
• When waves meet a gap in a barrier, they carry on
through the gap and spread out
• How much they spread out depends on how the width
of the gap compares to the wavelength of the waves.
• Lots of diffraction happens when the wavelength is
the same size as the gap.
Past paper question
The normal
v
light has moved from glass to air / from air to glass
value of v doubles but the
value of y does not double
value of v doubles but the
value of y does not double
As (angle) v increases, angle y increases
no evidence outside this range
Sound
•
•
•
•
•
•
•
•
Longitudinal waves
Echoes are reflections of sound waves
Sound can only travel in a solid, liquid or gas
A loud sound has a large amplitude
A quiet sound has a small amplitude
A high pitched sound has a high frequency
A low pitched sound has a low frequency
The normal range of human hearing is between about
20 Hz and 20 kHz
• The range becomes less as we get older.
• Sounds with frequencies above about 20 kHz are
called ultrasound.
Past paper question
Microphone
Loud speaker
Radio waves
Electrical vibrations
Light waves
Past paper question
It will go quieter
ELECTROMAGNETIC (em)
SPECTRUM
Contains 7 different types of radiation
Longest wavelength
Lowest frequency
Shortest wavelength
Highest frequency
(10−15 metres to 104 metres)
radiowaves
• Used for TV and radio
• TVs use higher frequencies than radios
• Diffraction allows radio signals to be received behind
hills and repeater stations are used to improve
reception
microwaves
• Used to transmit signals such as mobile phone calls.
• Microwave transmitters and receivers on buildings
and masts communicate with the mobile telephones in
their range.
Some mobile phones may be a
health risk.
 Others think that the intensity of
the microwaves is too low to
damage tissues by heating, and
microwaves are not ionising.
 Some wavelengths can be used to
transmit information to and from
satellites in orbit. Satellite TV
signals use microwaves.

VISIBLE LIGHT AND
INFRARED
VISIBLE LIGHT
• Visible light helps us to communicate via sight
• Cameras and video recorders use visible light
• Very bright light damages our eyes
INFRARED
Infrared is used in toasters,
heaters and grills and can cause
burns
 Used in burglar alarms, remote
controls and security alarms

Past paper question
to compare mobile phone usage
between the two groups
enough data to indicate relationship
or reduce effect of anomalous data
Past paper question
Past paper question
1. Research may be biased (in favour of
companies)
2. Negative effects on health may not get
published
1. It allows people to easily identify lower
risk phones
2. And this allows people to make a more
informed choice
The big bang
• Theory – an idea but not a fact
• The theory states that originally all the
matter in the universe was concentrated
into a single incredibly tiny point.
• This began to enlarge rapidly in a hot
explosion (called the Big Bang), and it is
still expanding today.
• The Big Bang happened about 13.7 billion
years ago
Evidence for
the big bang
• Cosmic microwave background
radiation (CMBR) – thought to be left
over heat from the original explosion
• Red-shift
Explaining the
Doppler effect
• When a police car goes past, its siren is high-pitched
as it comes towards you, then becomes low-pitched
as it goes away.
• When a source (e.g. galaxy) moves towards an
observer, the observed wavelength decreases and
the frequency increases.
• When a source (e.g. galaxy) moves away from an
observer, the observed wavelength increases and the
frequency decreases.
Red-shift
• When an object (e.g. galaxy) moves away from an
observer, its light is affected by the Doppler effect
• We know our sun has helium in it because there are
black lines in the spectrum of the light from the Sun
where helium has absorbed light. These lines form the
absorption spectrum for helium.
• When we look at the spectrum of a distant star, we still
see an absorption spectrum. However, the pattern of
lines has moved towards the red end of the spectrum, as
you can see above.
Red-shift
• The positions of the lines have changed because of
the Doppler effect. Their wavelengths have increased
and their frequencies have decreased.
• The further from us a star is, the more its light is redshifted. This tells us that distant galaxies are moving
away from us, and that the further away a galaxy is,
the faster it's moving away.
• Red shift tells us how far away a galaxy is and the
speed at which it is getting further away from us
More Evidence for the Big Bang
Red shift is not the only evidence for the Big Bang.
Another key piece of evidence for the Big Bang theory is
cosmic microwave background radiation (CMB).
CMB is electromagnetic radiation that fills the whole of the
Universe and comes from every direction. It is the left over heat from the
Big Bang. The expansion of the universe has stretched the waves so they
are now microwaves.
NASA’s COBE satellite,
launched in 1989,
provided vital evidence for
the Big Bang theory by
measuring CMB.
Stephen Hawking said this
picture ‘shows the mind of
God’
Past paper question
1. Distance from Earth
2. Speed stars / galaxies are
moving (away from Earth)
3. Supports theory that the
Universe is expanding / Big Bang
theory
Past paper question
1. The microwave radiation comes from
radiation present just after Big Bang
2. The Big Bang theory is currently the only way
of explaining CMBR
1. wavelength is decreased and frequency
increased
1. Big bang theory – universe started at
one point then expanded
2. Steady state theory – universe has no
origin / has always existed
1. Wavelength of light increases / frequency of light
decreases
2. or wavelength / light moves to red end of spectrum
1. Red-shift is evidence / supports idea of expanding
universe
2. Both theories use the idea / accept / explain why the
universe is expanding
1. to find evidence to support one or both
theories or to find evidence to disprove one
or both theories
1. Religious belief or no / insufficient evidence