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Transcript
Physics 1 revision facts

Heat energy moves from a hotter object to cooler surroundings

Heat energy is transferred in one of 3 ways
- conduction – vibrating particles pass on their energy to the particles next to
them. The main form of heat transfer in solids
- convection – particles with the most energy move from the hotter place to
the cooler place and take their heat energy with them. The main form of heat
transfer in liquids and gases.
- radiation is the transfer of heat energy by electromagnetic waves and
occurs in solids, liquids and gases

The bigger the temperature difference the faster heat is transferred

All objects are continually emitting and absorbing heat radiation

The bigger the surface area the more waves can be emitted from the surface so the
quicker the transfer of heat

Radiation depends on surface colour and texture

Dark matt surfaces absorb heat much better than bright glossy surfaces

Silver surfaces reflect nearly all radiation falling on them

Conduction of heat is the process where vibrating particles pass on their extra kinetic
energy to neighbouring particles

Metals are good conductors because they have free electrons, which can move
through the object and transfer heat

Convection occurs when the more energetic particles move from the hotter region
to the cooler region and take their heat energy with them.

Convection currents are all about changes in density. Hot water/air is less dense.
Less dense water/air rises and cool water/air is more dense and sinks

Kinetic theory explains the 3 states of matter.

The particles in a solid are tightly packed together with strong forces of attraction,
unable to move but can vibrate around a fixed point.

The particles in a liquid are still packed together, but with weaker forces of
attraction, can move past each other at low speeds.

The particles in a gas are spaced out, almost no forces of attraction, free to move in
any direction at high speeds.

Condensation is a gas turning into a liquid. As the gas cools the particles slow down
and lose energy. The attractive forces pull them closer together so the gas becomes
a liquid

The rate of condensation will be faster if
 the surface temperature of the liquid is lower
 the surface area of the liquid is larger.

Evaporation is a liquid turning into a gas. As the particles at the surface of the liquid
heat up and gain energy they can escape.

The rate of evaporation will be faster if
 temperature of the liquid is higher
 the density of the liquid is lower
 the surface area of the liquid is larger
 the airflow over the liquid is greater.

The rate an object transfers heat energy depends on
 Surface area – the bigger the surface area the more infrared waves can be
emitted = faster rate of transfer
 Volume – the smaller the volume the faster the rate of transfer
 Material – conductors transfer at a faster rate, darker matt surfaces transfer at a
faster rate
 Temperature difference – the bigger the temperature difference the faster the
rate

Vacuum flasks are designed to reduce heat transfer
 Plastic cap – reduces conduction
 Plastic casing – reduces conduction
 Shiny silver insides – reflects heat back onto liquid
 Double glass wall, filled with air – stops conduction and convection

Insulation reduces heat loss from homes
 Loft insulation – reduces conduction and radiation
 Cavity wall insulation – reduces convection and radiation
 Hot water tank jacket – reduces conduction and radiation

Payback time = initial cost of insulation / annual saving

U-values show how fast heat is transferred through a material

The higher the value, the faster the heat transfer

The better the insulator the lower the U-value

Specific heat capacity is the amount of energy needed to raise the temperature of
1kg of a substance by 1oC.

Specific heat capacity can be calculated by (DON’T NEED TO LEARN)
Energy transferred (J) = mass (kg) x specific heat capacity (J/kgoC) x temp change (oC)

There are 9 types of energy – electrical; light; sound; kinetic; nuclear; thermal;
gravitational potential; elastic potential; chemical

Potential and chemical are forms of stored energy

Energy can never be created or destroyed it can only be converted

Energy is only useful when it is converted from one form to another

Energy transfers involve losses often as heat

The efficiency of any device is defined as
useful energy output / total energy input

Efficiency is usually given as a percentage

No device is 100% efficient and the wasted energy is always as heat.

All types of energy are measured as Joules (J)

Electrical devices convert electrical energy into heat, sound, light etc.

Batteries convert chemical energy into electrical energy to run devices

Electrical generations always involves converting other forms of energy into
electrical energy

Gravitational and elastic potential energy always get converted into kinetic energy
first

The units of energy are Kilowatt-hours (kW-h)

A kilowatt-hour is the amount of electrical energy used by a 1kW appliance left on
for 1 hour

Energy = power x time

Energy is measured in joules and power is measured in watts

Number of units (kW-h) used = power (kW) x time (hours)

Cost = number of units x price of units

Non renewable energy resources will run out one day. These are coal, oil, gas and
nuclear fuels.

Coal, oil and gas are burnt in a power station to heat water, to produce steam. The
steam turns a turbine, which turns a generator which produces electricity.

All 3 fossil fuels release carbon dioxide. Burning coal and oil releases sulphur dioxide.
These both cause pollution, and can cause global warming, acid rain and climate
changes

Nuclear reactors use nuclear fission to heat the water to produce the steam, to turn
the turbine, to turn the generator.

There is no pollution as nothing is being burnt.

Renewable energy resources will never run out. They are wind, wave, tides,
hydroelectric, solar, geothermal, food, biomass.

These resources are designed to turn the turbines directly, which turns the generator
to produce electricity.

They damage the environment less than non renewable, but don’t provide as much
energy

Electricity gets around via the national grid.

Electricity is carried at very high voltage and low currents as it is cheaper

The voltage used is 400 000V. It requires transformers and large pylons to carry the
electricity at this voltage

Transformers alter the voltage. They step it up (increase it) at one end and step it
down (lower it ) at the other.

Electromagnetic waves carry energy not matter

Wavelength is the distance from the peak of one wave to the peak of the next

Frequency is how many complete waves there are per second. Measured in hertz. 1
Hz is 1 waves per second

Amplitude is the height of the wave from the midline to the peak

Wavespeed is how fast the wave travels

In transverse waves the vibrations travel at 90o to the direction of energy transfer of
the wave

Most waves are transverse e.g. light and electromagnetic waves

In longitudinal waves the vibrations are parallel to the direction of energy transfer of
the wave.

Sound waves and ultrasound are examples of longitudinal waves

Wavespeed (m/s) = frequency (Hz) x wavelength (m)

Reflection of light allows us to see objects

Light travels in straight lines

The normal is a line drawn at 90o to a surface

Angle of incidence = angle of reflection

An image formed in a plane mirror is
 Same size as the object
 Same distance from the mirror as the object
 Virtual (appears to be coming from a different place)
 Upright
 Laterally inverted

Diffraction is the spreading out of waves. This happens if a wave passes through a
gap.

The amount of diffraction depends on the size of the gap

The narrower the gap, or the longer the wavelength, the more the wave spreads out

Refraction is the bending of a wave due to a change in medium

As light passes from a less dense medium into a more dense medium (e.g. air into
glass) the light ray bends towards the normal

As light passes from a more dense medium into a less dense medium (e.g glass into
air) the light ray bends away from the normal

The electromagnetic spectrum is made up of
Radiowaves
Microwaves
Infrared
Visible light
Ultraviolet
X-rays
Gamma rays
Low frequency
High frequency
Long wavelength
Short wavelength
Low energy
High energy

EM radiation can be absorbed, reflected or transmitted

When it is absorbed it can make the object hotter or set up an tiny alternating
current with the same frequency as the EM wave

Radiowaves can pass through soft tissue without being absorbed

Microwaves are absorbed and cause the cells to heat up

UV rays can cause skin cancer

Radiowaves are used for communications

Microwaves are used for satellite communications and in mobile phones

Optical fibres use visible light and infrared

UV is used in sunbeds and fluorescent light tubes

X-rays are used in hospitals

Sound travels as a wave

Sound is caused by vibrating objects. These vibrations are passed through
surrounding mediums as a series of compressions

The sound eventually travels to someone’s ear

Sound cannot travel in a vacuum (no particles)

Humans can hear sounds with a frequency between 20-20000Hz

Sound waves can reflect and refract

Echoes are reflected sound waves. There will be a delay between the original sound
and the echo as the sound has further to travel.

High frequency sounds have high pitches

Low frequency sounds have low pitches

The Universe began with the Big Bang – an explosion which occurred from a single
space. The universe then started expanding and still is.

Cosmic Microwave Background Radiation (CMBR) is low frequency electromagnetic
radiation with was thrown out during the Big Bang – proof of it happening.

Red shift is more proof that the Big Bang occurred.

Light from distant galaxies are at a lower frequencies than they should be. It is shifted
towards the red end of the visible spectrum. The further away a galaxy is the bigger
the red shift.

This means the more distant galaxies are moving away from us faster than nearer
ones

This provides the evidence that the Universe is expanding and supports the big bang
theory
.