Physics modular 1

Energy is neither created nor destroyed, it merely changes from one form to another.

The Gravitational Potential Energy of an object depends on how high and the position that object is above a surface. When released the gravitational potential energy will diminish and the object will gain kinetic energy. It can be used as a store for energy (hence the word 'potential').

Kinetic Energy depends on how fast the object is moving, the faster it goes the higher the kinetic energy it has.

Elastic Potential Energy (sometimes called 'stretch or compressed' potential energy) is found in springs, elastic materials. It comes from the structure of the materials and their desire to retain a particular shape. It can be used as a store for energy.

Chemical Energy is energy stored because of the chemical makeup of a substance. It is determined by the bonding sturcture. Ice at O^OC has less energy than water at O^OC. It can be used as a store for energy. This energy can be released by burning or other reactions. Chemical energy is used in a system when a chemical change takes place.

Sound Energy can be detected by our ears. Movement causes the air molecules to vibrate and when this vibration of the air molecules is great enough, it can be detected as sound. Most things that have moving parts convert some of their energy to sound energy.

Light Energy is a form of electromagnetic radiation . Light energy can be detected by our eyes. When a system converts some of its energy into light energy, heat energy often accompanies it, as this is part of the same family.

Heat Energy can be detected by our skin. When it travels from the source by contact we call its method of conduction. In gases and liquids it also travels by convection and it travels directly in the form of electromagnetic radiation called infra red radiation. Heat energy is almost certain to be found as an energy transfer in a system. It can often be a nuisance in an energy transfer system design.

Electrical Energy derives from the movement of electrons (the kinetic energy of electrons). It is a very convenient form of energy and we make a great deal of use of it today.

Magnetic Energy is produced by moving charges. Some elements; cobalt, iron and nickel are said to be ferromagnetic and are attracted to magnetic objects and can be made into magnetic objects themselves. When a current passes through a wire a magnetic field results (because the electrons are moving in the wire). This cannot easily be detected, but when conducting wire is wound into a coil the effect is detectable with a small compass.

Energy isn't always used, this is not useful energy we are shown this by sankey diagrams, they represent 'to scale' the energy transfers.

energy input --------> useful energy
                      ||
                      v
Wasted or unwanted energy forms (width represents the amount of energy)
Candle
           chemical energy -------------> light energy
                                            |
                                       heat energy

energy input --------> useful energy
                      ||
                      v
Wasted or unwanted energy forms (width represents the amount of energy)
Candle
           chemical energy -------------> light energy
                                            |
                                       heat energy

Efficiency = useful output/ total input

input = 20 -----> useful is 6       
                  |
             wasted 14

6/20 = 0.3

There are two types of energy - mechanical energy and electromagnetic energy

Mechanical Energy

passed on by particle vibration
travel best throughsolids sound and siesmic

Electromagnetic Energy

Pure energy packets (photons) no mass just energy - travel best through a vacuum
Parts of the Electromagnetoc Spectrum

Waves of energy al travel at the same speed through a vacuum, that speed is called the speed of light the symbol given to it is c.

c = 3x10⁸ m/s
c = 300,000,000 m/s

The sun rays take 8.3 minutes to reach us. The stars light takes at least four years.

The speed of light is the fastest anything can travel at.

The elctromagnetic spectrum is a family of waves with wave lengths.

Wavelengths vary from much smaller than nanometres up to hundreds of kilometres in wavelength. The higher the frequency of the wave the smaller the wavelength.

wavespeed = frequency x wavelength(c = fl)

Everything is made up of atoms. Each element has a different number of protons in the nucleus. They are listed in order of the number of protons. The nucleus of the atom is ery tiny and it is orbited by electrons.

Electrons move at high speeds within a vast empty space arounf the nucleus. The higher the energy the furthur out their orbit is.
Tiny dense nucleus containing most the mass of the atom packed into a very small volume. It is positively charged because the protons are positive.
The number of neutrons determines which isotope of the element we are dealing with - this does not change its chemical properties but does change physical properties
The number of protons determines which element we are dealing with.
Equal numbers of protons and electrons make an atom neutral.
If there are fewer electrons than protons we have a positive ion - which is attracted to the cathode
I there are more electrons than protons we have a negative ion - sttracted to an anode.
proton = charge +1, mass 1, inside nucleus
neutron = charge 0, mass 1, inside nucleus
electron = charge -1, mass 0.00055, orbitting nucleus 

The orbitting electrons can move between two different energy levels. When they are close to the nucleus they are of a lower energy. When they gain energy they can move to a higher energy level. 'If they fall down' to a lower energy they give out the energy they have lost as electromagnetic radiation.

If you have a iron bar that is heated, you can feel the heat coming from it. These heat rays are infra red radiation. They are heat rays given out as the electrons fall back to their lower energy state. If you heated the iron bar enough it would glow this is electromagnetic rays of visible light given out by electrons falling back from a higher energy state. 

All of the electromagnetic spectrum except gamma rays are given out when electrons change energy.  

Atroms sometimes lose or gain electrons in chemical reactions
Protons are positive and Electrons are negative
Neutral atoms have the same number of protons and electrons
Negative ions have gained electrons
The positie Ion has more protons than electrons, it has lost electrons

Electromagnetic radiation is absorbed by electrons this makes them jump to higher energy levels if the absorb very high energy rays they can jump clear of an atom and make it an Ion.

Electromagnetic radiation that is able to do this is called Ionising radiation. This can be dangerous to us as if atoms within our DNA are ionised it can lead to cell mutations and cancers.

Your body has an immune system that recognises rogue cells and kills them before they can do any damage this is relatively easy to do if the damage is widely spread but if the damage is concerntrated in a small area the immune system can not cope and you are more likely to develop cancer this is also true if your immune system is weak.

Gamma radiation is very penetrating and can penetrate deep into matter. The Ionisationfrom Gamma rays is therefore widely spread. If you swallowed a gamma emitter most of the rays would come striaght through the body and out to the surroundings. This is used in medical procedures. A chemical that emits gamma rays is injected into your blood stream and the doctors use the gamma rays to find out where the chemical has accumulated.

Ultra-violet radiation is only Ionising if the radiation is of higher energy it can not penetrate deeply into the body it doesn't get through the skin all the damage it does to the skin and the corneas of the eyes.

X-rays are also very penetrating therefore the Ionisation is wisely spaced and X-rays can also be used in medicine. Xray rays are not given out by atoms like gamma rays they are made by a machine that fires very fast electrons at a metal target.

Heat is a form of energy measured in joules

Temperature is a measure of how hot or cold something is. It is measured in degrees celsius or kelvin. The same amount of heat will have differing effects on different amounts of fluid.

Heat transfer is the transition of thermal energy from a hotter mass to a cooler mass. The three main types of heat transfer are conduction, convection and radiation.

Heat causes the molecules in a solid to vibrate.

introduced heat ----> ||Io|o|oo         o= molecule | = vibration

object heated -----> ||o||o||o||o||

If we heat one end of the solid the vibrations will increase and increase the neighbouring molecules to vibrate more. The heat energy is conducted through the solid.

Metals are excelent conductors of heat because they have free electrons which can move around the metal and distribute the heat energy throughout the metal and distribute the heat energy throughout the metal more quickly.

Exam answer

Metal always feels cold to touch and carpet feels warm on your feet because metal being a dense solid requires a lot of energy to pass from your body to warm up. It also has a reasonable rate of heat conduction, so the surface remains cold for sometime when in contact with your body. Carpet on the otherhand has a smaller number of density because most of the volume is occupied by air. It therefore warms up very quickly to the temperature of your skin, at which point it is preventing furthur heat loss and feels warm. In reality the carpet never reaches the temperature of your skin, because it is constantly being colled by the replacement of warm air with cool air. so unlike metal, the main colling process for carpet is not conduction but convection.

Insulators are materials whise atoms have tightly bound electrons. An insulator has negligible thermal conductivity.

It is important to prevent heat escaping from our houses, wasting energy is not only a waste of money but it adds to our carbon footprint which leads to global warming.

Three ways of insulating houses:

loft insulation - prevents heat loss when the hot air rises, the insulator stops the heat energy escaping from the roof

Cavity Walls - prevents heat escaping through the walls

Double Glazing - prevents heat escaping through the windows

Convection is the transfer of heat through a fluid, by molecular motion.

A fluid is a substance that flows - gas or liquid

A convection current is when hot air rises and is replaced by cooler air. This cooler air wil then gain heat energy and begin to rise. As the hotter air meets the cooler air it transfers its energy and becomes cooler, so the whole process starts again.

When a gas is heated the movement of the particles becomes greater and therefore the same mass of particles taking up a larger space.

This means that the gas has become less dense and therefore gas with a greater density will fall to take its place, forcing the less dense gas upwards. 

    ^-------->
    |        |     hot air rising
    |        |     cool air falling
    <____v

During the day, the sun shines on the land and the sea.
It requires more heat energy to raise the temperature of the sea so the land becomes hotter than the sea.
The land then heats the air above it causing it to become less dense it is then replaced by cooler air from above the sea and we have a breeze.

      ^---------> -----------> 
      |                         | 
      |                         |
       < ____ < _____  v
=========mmmmmmmm

warm                 cool

At night, the land loses heat at a faster rate than the water

This can cause the air above sea to become warmer then the air above the land so the convection current moves in the opposite direction

        <---------- <------- ^
      |                         | 
      |                         |
      V _____ > _____>   .

=========mmmmmmmm

      cool             warm

Radiation is a transfer of heat energy through electromagnetic waves.

Radiation occurs in the infra red part of the spectrum.

As radiation travels in waves it does not need a medium like conduction and convection do. It can therefore travel through a vacuum, which is why the sun's energy can reach us from space.

All matter emits radiant energy. The hotter an object is compared to its surroudings, the faster it will radiate heat.

The physical qualities of an object dtermine its ability to absorb or reflect radiation.

Dark, rough and dull surfaces generally absorb and emit radiation well.
Smooth, shiny surfaces are usually good reflectors of radiation and therefore do not emit radiation.

Inside a vacuum flask there is a double glass shell. Betweenthese layers of glass is a vacuum.

The vacuum prevents any heat transfer through conduction or convection.

The glass shell is coasted with a shiny reflective material.

The silver reflects the heat to keep more in there is no dull surface because we do not want to emit heat. We want the contents to remain a constant heat.

Anaogue signals - vary constantly in ampitude or frequency or both. The signal can have any value

Digital Signals - are a series of pulses with only two states ON or OFF (0 or 1). There are no values in between

Noise

Signals become weaker as they travel further distances and may also pick up random extra signals. The distortion of the original signal is called noise. Noise can be heard as crackles and hissing on radio programmes.

Advantages of Digital Signals
-- any noise can usually be ignored by amplifiers
-- Quality is maintained over longer distances
-- More information can be carried per second
-- Can be transmitted along optical fibres (cheaper to transmit)

Microwaves  are a part of the Electromagnetic spectrum .

Microwaves have a frequency range of 300 MHz to 300 GHz. This positions them between radiowaves and infra red.

A microwave oven uses microwave radiation to cook food. The frequency of the waes causes the water molecules within the food to vibrate faster and raise the temperature of the food.

Leave the food for a few minutes because once the microwaves have stopped being transmitted the heat energy of the water molecules has to be conducted to the rest of the food.

wave equation = v = fl

speed = frequency x wavelength
speed of light = 3.0 x 10⁸

 l = v/f =  3 x 10^{8
                ---------------}                      = 300,000,000
           300,000,000,000

=0.001 = 1/1000 = 1mm -1m

Microwaves range from one metre to 1 millimetre

Both radiowaves and microwaves are used in communication. Radiowaves have a longer wavelength than microwaves and can't penertrate the atmostphere. The higher the frequency the higher the radiowave can get into the atmostphere before it is reflected.

High wavelength low frequency
Low wavelength high frequency

Radio - slower
Microwave - quicker, high frequency = more energy

As microwaves have a higher frequency they can penetrate the Earth's atmostphere and can therefore send data to and from Satellites.
Microwaves are said to be non-ionising which means they can't change DNA and cause cancers

SAR - Specific Absorption Rate which is a measure of the rate at which radiation from your phones is absorbed by our head

The Electromagnetic Spectrum contains a very big range of wavelengths and frequencys. Some of these are absorbed by the atmosphere some are not.

The visible part of the Electromagnetic spectrum gets through the atmosphere. Some of the ultra- violet gets through. Frequencys higher than ultra-violet light are completly absorbed by the atmosphere. Infra-Red is partially absorbed, but there is no pattern linked to its wavelength that can describe how this absorption happens.

The increase of green house gases means the amount of infra-red absorped by the atmosphere has increased. The high energy infra-red gets through the atmosphere easier than the lower energy infra-red. That means the infra-red from the Sun easily gets through the atmosphere, but the lower energy infra-red emmitted by objects the Sun warms tends to get absorbed by our atmosphere.

Microwave radiation gets through the atmosphere easily so it is used for satellite communication. RadioWaves get absorped therefore are not used for satellite communication.

First telescopes were optical systems - using lenses and mirrors
They gave a magnified image and allowed us to find out about the planets and moon.

Todays telescopes not only detect visible light detect all parts of the electromagnetic spectrum.

The intensity of the microwaves etc and the frequency and wavelength of them is transferred into a visible image by a computer.

The atmosphere absorbs a lot of the electromagnetic radiation that comes from outer space 'to see' through the atmosphere is difficult.

telescopes are put in very high places, so the radiation doesn't have to travel far to get through the atmosphere - images will be picked up much better.

You can get even better information by putting the telescope on a satelite orbiting the Earth 

When light or sound waves are entitled from a moving body the waves get bunched up infront and spread out behind. The light from a moving body looks bluer infront and redder behind. This is called red shift and it is this that led scientists to discover that lots of galaxies are moving away from us.

wave speed = frequency x wavelength

Having a longer wavelength means the frequency will be low because it always happens as it is a pair like the shorter the wavelength the higher the frequency.

Ionisation
If an atom or molecule is ionised, electrons are added or taken away. Extra electrons cause a negative charge and loss of electrons cause a positive charge.

Isotopes
If an atom gains extra neutrons it is called an isotope. This is unstable and is radioactuve.

Radioactive substances
Radioactive emissions come from the nuclei of atoms. Chemical reductions or heating do not change the radioactivity.

Bakground Radiation
Background radiation is from our surroundings which we are exposed to on a daily basis:
natural - radon gas from the ground, gamma rays from the ground and buildings, from food and other body chemicals, cosmic rays from space
man made - madical sources, nuclear power, nuclear weapon testing

Alpha Decay
When a radioactive isotope gives out an alpha particle two protons and two neutrons are given out of the nucleus

The alpha particle can be written as 4 He
                                                    2
Americium is an element which decays by emitting alpha.
 241Am -------> 237Np  + 4 alpha
   95                 93         2

Beta Decay
When an element decays by beta by beta decay a neutron in the nucleus becomes a proton. An electron is released and this is emitted out of the atom. The electron is known as a beta particle, often called 0 e
                                                       -1
Gamma Decay
An unstable nucleus can decay by emitting a gamma ray from its nucleus. This does not change the form of the atom and so it is still the same element.  

alpha - 2 protons+ 2 neutrons, +2 positive charge, 4u heavy mass, slow speed, Most ionisation, short range 2-3cms, stopped by paper or skin

beta - a neutron turned into a proton and electron released, -1 negative charge, 1/2000u very light, quick speed, medium ionisation, medium range in air 1-2ms, stopped by aluminium

Gamma - electromagnetic wave, no charge, no mass, speed of light, least ionisation, long range in air 1 km, stopped by 5cm lead

This deflection happens when the magnetic field is at right angles

1 = beta
2 = gamma
3 = alpha