Habitat

The physical environment that an organism (or a population of organisms) lives in is called it's Habitat. It can be described using the biotic and abiotic factors we have been looking at. For each of the biotic features an organism will have a prefered niche range. Outside this range the some organism will may survive in a marginal niche, but will be stressed. Large variance from the prefered niche normally causes the organisms to avoid those conditions (if mobile) and may cause death.




The above graph show plant growth at a range of temperature. In class we looked at a W.A. study on trout which found their prefered niche was 8 - 17 oC. The study also showed trout could survive in water as cold as 2oC and as hot as 27oC, but outside the prefered range they were unlikely to breed. The study also looked at other factors such as pH, and salinity.


We also looked at Dingo habitats and saw that a very mobile animal such as a Dingo may have everal types of habitat in a pack's home range such as Hills, Woodland and Riverine in order to provide all the water and prey the pack needed. The dingos seemed to prefer the productive wooded riverbanks and spent a large proportion of their time in these areas only occasionally visiting the rocky mountainous areas in their range.

Earth’s components

The Hydrosphere – includes all the water found on Earth (Lakes, ponds, oceans ice caps and even water vapour in the air. All organisms depend on water for their metabolism; most chemical reactions take place in water. (Remember Hydro means water in Greek.)

The Atmosphere – the envelope of air that surrounds the Earth. It is often subdivided into four zones (called from lowest altitude to highest: the troposphere, stratosphere, mesosphere and thermosphere) (Remember atmos means air or vapour in Greek.)


The Lithosphere – the outermost solid layer of Earth, its crust and upper mantle. It is made of the large mobile plates we studied in geology both land masses and under the ocean floor. In this topic we will be most interested in the rock and soil types. (Remember litho means rock in Greek.)


These entire three systems link together to form a Biosphere, a region that supports living things (or biota.) It is common to subdivide the Biosphere into regions characterised by their main plant types.

These regions called Biomes include deserts, tundra, tropical rainforest, savannah, and alpine areas.

The Ecosystem describes the way organisms are found together in a physical place. Both physical (abiotic) and biological (biotic) factors describe an ecosystem. Examples of abiotic factors may be: wind speed, humidity, rainfall, soil type, air temperature etc. While biotic factors may include the presence of producers, parasites, competitors, pathogens and decomposers in the community

Radio Signals

When you tune in your radio you are listerning to information sent by a broadcaster as a carrier wave. There are however two ways to modulate this underlying carrier wave signal. On your radio there will be an AM/FM switch to swap between radio stations that use these two methods.

FM radio works the same way that AM radio works. The difference is in how the carrier wave is modulated, or altered. With AM radio, the amplitude, or overall strength, of the signal is varied to incorporate the sound information. With FM, the frequency (the number of times each second that the current changes direction) of the carrier signal is varied.

FM signals have a great advantage over AM signals. Both signals are susceptible to slight changes in amplitude. With an AM broadcast, these changes result in static. With an FM broadcast, slight changes in amplitude don't matter -- since the audio signal is conveyed through changes in frequency, the FM receiver can just ignore changes in amplitude. The result: no static at all.

Digital radio only needs to carry on/off digital information, like a computer or a cd, so digital radio uses the AM system.

Radio waves like all other forms of electromagnetic radiation travel at the speed of light (300 000 000m/s).

Our wave equation says that:

velocity (metres per second) = frequency (hertz Hz) x wavelength (metres)

which can be written i short as: v= f ƛ

Radio stations normally give their frequencies in KiloHertz. For example ABC Melbourne is on 774 KHz so has a wavelength of 300 000 000 / 774 000 = 388m

electromagnetic radiation

Unlike the water waves in a ripple tank, that are oscillating water molecules, or sound waves, that are oscillating air molecules in light waves there are no actual physical particals that move. Instead light is made from electric feilds and magnetic fields oscillate together (but perpendicular to each other.)

Light, electricity, and magnetism are manifestations of the same thing called electromagnetic radiation. The energy you see coming out of the computer screen you are using to read this page is made of fluctuating electric and magnetic energy fields. This energy comes in many forms, some have wavelengths that are detectable by our eyes but others can not be seen such as infrared (IR), radio, X-rays, ultraviolet (UV), and gamma rays.

All these electromagnetic waves carry energy and we can use it in many different ways for example ultraviolet light has high enough energy to damage our skin cells (we tan as a defense mechanism). Special UV bulbs called ``black lights'' are used by hospitals to kill bacteria. Because X-rays have such high energy they can pass through skin and muscle but are stopped by bone.

The link below to go to a diagram of different wavelengths of electromagnetic radiation and some of the properties of the different parts of this spectrum.

http://en.wikipedia.org/wiki/File:EM_Spectrum_Properties_edit.svg

Resonance

All objects have a natural frequency of vibration.

If an object if forced to vibrate at its natural frequency it will vibrate at its maximum amplitude.

We call this effect Resonance.

The larger the mass of an object, the lower its natural frequency.

We did an experiement in class with test tubes partially filled with water so that each contained a column of air. The one with the shortest column of air (most water) had the least mass of air and therefore the highest frequency, the empty tube, with the greatest mass of vibrating air had the lowest frequency. Similarly on a guitar the thickest string (the one with the most mass) has a low freqency (deep note) while the thinest string has the highest note.


You may have seen film of a singer finding a glasses natural frequency and causing the glass to shatter. In class we looked at a movie of the wind causing the old Tacoma Narrows Bridge to resonate at it's natural frequency.

Diffraction

Diffraction
When waves meet a gap in a barrier, they carry on through the gap. However, the waves also spread out to some extent into the area beyond the gap. This bending of the waves is called diffraction.

The amount of diffraction depends on the wavelength and the size of the gap. The smaller the width of the gap compared with the wavelength of the wave, the stronger the diffraction.

For example, when in Melbourne you may have noticed waves at St.Kilda, Elwood Beach, Williamstown, or Frankston. These waves have all passed through the narrow gap into Port Phillip from Bass strait.

Diffraction of Different Types of Waves

Sound
Sound can diffract through a doorway or around buildings. Lower pitched sounds travel better than high-pitched sounds. This is because low-pitched sounds have a long wavelength compared with the width of the gap, so they spread out more.

Ultrasound
Ultrasound is sound with a high frequency. It has a very short wavelength compared with most gaps, so there is very little spreading. This makes sharp focusing of ultrasound easier, which is good for medical scanning.

Light
Light has a very short wavelength compared with most everyday gaps such as windows and doors. There is little obvious diffraction, so it produces sharp shadows.

Radio waves
Long wave radio signals are much less affected by buildings and tunnels than short wave radio signals or VHF radio signals. Because of diffraction, radio signals can sometimes be received in the shadow of hills.

REMEMBER - as well as behaving like a wave (reflecting, refracting diffracting and interfering) electromagnetic radiation also can act as a particle just like we saw in the spinning wheel demonstration where the light particles (or photons) were able to spin the wheel because they had momentum (and therefore mass.)

Interference

This week in year 10 we are looking at wave interference : That is the combining of two or more waves that meet at one point in space.

Terminology:

SUPERPOSITION OF WAVES:
When two or more waves interfere, the resultant wave's amplitude equals the sum of the signed amplitudes of the interfering waves.

CONSTRUCTIVE INTERFERENCE occurs when waves interfere in such a way that the amplitude of the resulting wave shows positive growth.

DESTRUCTIVE INTERFERENCE occurs when two or more waves interfere in such a way that the amplitude of the resulting wave shows negative growth.

There are two special cases of interference where the wavelength, and amplitude are the same for both the original waves.

IN PHASE: Wave 1 and wave 2 are said tobe in phase both waves have the same wavelength and rise and fall together.
This leads to constructive interference, and the resultant wave's amplitude equals the sum of the individual wave amplitudes. Here, the resultant amplitude is twice as large as wave 1's (or wave 2's).

OUT OF PHASE: Here wave 1 and wave 2 are out of phase, because wave 2 looks like wave 1 shifted half of its wavelength to the right. This leads to deconstructive interference, and since wave 1 and wave 2 also have the same amplitude, the waves completely cancel each other out and the resultant wave has an amplitude of zero.

Refractive Index

The refractive index of a substance is a comparision of the speed of light in that material to the speed of light in a vacuum.

This will be slightly different for different frequencies (colours) of light, and are normally quoted using an orange sodium light.

Light is bent towards the normal as it passes into a more dense material (eg air into water) and away from the normal when it speeds up by entering a less dense material (eg glass into air)






Every substance has its own index of refraction.
Here are a few examples:-
Water 1.33 Glass 1.50
Quartz crystal 1.54 Glycerin 1.47
Diamond 2.42



The angle of incidence θ1 is related to the angle of refraction θ2 by the formula (left) where n1 and n2 the refractive indices.





In class we bent light towards the normal by passing it from air through a perspex block, and then away from the nnormal as it came out the other side. In my case the angle of incidence θ1 was 43 degrees, and the angle of refraction θ2 was 28 degrees.


Now we know that Sin 43 = 0.681 and that Sin 28 = 0.469,
also that the RI air = approx 1 (same as a vacuum)

so using the formula above 0.681 / 0/469 = RI perspex 1.45

Compare this to your results.

Can we now use our knowledge of refraction to understand a rainbow ?

Waves

Waves are a means by which energy travels.

There are many different types of waves. For example the waves on an ocean are physical waves caused mainly by wind. Light is an electromagnetic wave caused by excited electrons moving. Sound also moves in waves with the air particles moving backwards and forwards creating areas of different pressure.

Last week we looked at:

Reflection - when waves, whether physical or electromagnetic, bounce from a surface back toward the source. A mirror reflects the image of the observer.

and

Refraction - when waves, whether physical or electromagnetic, pass from one material into another they are deflected. The wave generally changes the angle of its direction because it's velocity changes. As it moves from a less dense to a more dense material it it bends towards the normal.

This week we are looking at a third property of waves:

Diffraction - when a wave goes through a small hole it's edges are bent and it flares out. Diffraction is a characteristic of waves of all types. We can hear around a corner because of the diffraction of sound waves. For instance, if a wall is next to you when you yell, the sound will parallel the wall. The wall may stop, but the voice doesn't; sound will almost turn the corner of the wall. This is diffraction.