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toc **Welcome to PhysicsScience**
This wikispace has been developed for the use of pupils from Selly Park Technology College to help them them with their learning and understanding of the New GCSE Science specification, P1 Universal Physics =**Topic 1 - Visible light and the solar system.** =

__Geocentric Model__
Claudius Ptolemy (C. AD90-168) like most Ancient Greek thinkers believed that the Earth was the centre of the universe. He thought that the Sun, Moon, planets and stars moved around the earth in circular orbits.This model was called the **Geocentric model** of the universe.



'Geo' comes from the Greek word for Earth.

__Heliocentric Model__
For over 1000years this model of the universe was not challenged, no one found a better method of calculating the way the planets move until 1543. This was when the polish priest **Nicolas Copernicus** (1473-1543) published a book showing that the planets go around the sun in circular orbits. This was called the **Heliocentric model**.

'Helio' is Greek for Sun.

Copernicus lived before telescopes were invented, he studied the night skies using just his eyes and used his observations as evidence for his model.

__Galileo Galilei (1564-1642)__
Galileo Galilei lived at the beginning of the 17th century, when he heard about the invention of the telescope by a Dutch optician in 1608, he immediately made his own lenses and mounted them in a tube. The moment he turned his home-made telescope to the sky he made some amazing discoveries.

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__ **Astronomy** **today.** __

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__Refracting and Reflecting Telescopes__
Do you remember?

When light passes from one material to another its speed and direction changes. This is called refraction. All types of waves can be refracted. e.g.



A convex l ens is a glass block curved at both sides to make it thicker in the middle. It is called a converging lens because it bends light inwards.

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__Refracting Telescopes.__
A simple refracting telescope consists of two lenses, an objective lens and an eyepiece lens. The objective lens produces an image of a distant object at its focal point and the eyepiece lens magnifies the image.

e.g.



The magnification of a telescope or any optical instrument is how much bigger the image is compared with the object. The magnification of a refracting telescope is equal to the focal length of the objective lens divided by the focal length of the eyepiece.

e.g



__Reflecting Telescopes__


 * //Refracting//** telescopes have a few limitations:

1. When light is passes into a converging lens most of the light is refracted, however some of the light is also be reflected. This can cause the image produced to become fainter, and can cause problems when observing faint distant stars.

2. The objective lens of a telescope is the most important feature as it determines the amount of light that will be collected. Large objective lenses produce brighter and generally clearer images than smaller lenses, but large lenses are hard to produce, are very expensive and difficult to transport.

3. A major disadvantage of refractors is they produce colour-fringed images. This false color results from the inability of the objective lens to bring all the wavelengths of light (colours) to focus at a single point.

However **//reflecting//** telescopes do not have any of the above problems:

1. All the light from the distant object is reflected so there is no loss of clarity, making it easier to observe faint distant stars. 2. Mirrors are much easier and cheaper to produce. 3. Reflecting telescopes do not exhibit colour-fringing problems.



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__ Waves __

__ Transverse and Longitudinal Waves. __
Transverse waves e.g. electromagnetic waves Longitudinal waves e.g. sound waves.

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__ Wave Speed Equation (m/s) __





Now try these worksheets.

=Topic 2 - The electromagnetic spectrum=

All electromagnetic waves are transverse waves and they **__all__** travel at the speed of light in a vacuum.

The electromagnetic spectrum is continuous, but the radiations within it can be grouped in order of decreasing wavelength and increasing frequency. e.g.

The higher the frequency and shorter the wavelength the higher the energy of the wave. OR The lower the frequency and the longer the wavelength the lower the energy of the waves.

Remember - if you were to create a wave using a rope which would require less energy, along or short wavelength?

You MUST remember the order of the waves within the electromagnetic spectrum. Here is a rap to help you... media type="youtube" key="h5fAtx15-3M" height="349" width="425" align="center"

__ Uses of electromagnetic waves. __
You need to be able to describe some uses of electromagnetic radiation, and relate the harmful effects of excessive exposure to life.

Checkout this website,it is packed with information. [|The Electromagnetic Spectrum]

__**Radio-waves.**__ ** ﻿Uses: ** Radio-waves are used when transmitting television and radio programmes between different places.

They are also used to transmit information to satellites, however only Ultra High Frequency (UHF) radio-waves are able to pass through the charged layer of the atmosphere called the ionosphere. Radio-waves of lower frequencies are reflected and can be received over large distances.

Checkout this web page. [|How radio communication works]

Dangers of radio waves: None

**__Microwaves.__** **Uses of microwaves:** include cooking, satellite transmissions and mobile phone communication.



Dangers of microwaves : ﻿ ﻿internal heating of body cells

Microwaves can be absorbed by the water in the cells in our body. This can cause internal heating of body tissue which may damage or kill cells. While mobile phones have many benefits, some studies have linked there use with brain tumours and cancer, however it is too early to be certain of the effects, as mobile phone technology is relatively new and there have not been any long-term studies on the possible consequences to health.

People also have concerns about the health risks from the radiation from mobile phone masts. Some people claim that the radiation emissions interfere with electrical signals within the body and cause headaches dizziness or even cancer.



Checkout this webpage and decide for yourself.

[|Phone masts - a heath risk?]

__**Infra-red **__ 'Infra' means 'below'; infra-red waves are just below the red region of the visible spectrum hence the name infra-red 'below-red'.


 * Uses: ﻿ **include cooking, thermal imaging, short range communications, optical fibres, television remote controls and security systems.



All objects emit infra-red radiation. The hotter an object is the more energy it emits.Your body emits infra-red radiation. media type="youtube" key="4lInl4EPGjw" height="314" width="504"

**Dangers of infra-red radiation:** ﻿ Skin burns.

<span style="font-family: Arial,Helvetica,sans-serif;">Infra-red radiation are absorbed by the skin and is felt as heat, too much exposure will cause burns.




 * <span style="color: #0000ff; font-family: 'Comic Sans MS',cursive; font-size: 170%;">__Visible Light__ **


 * Uses: ** ﻿include vision, photography and illumination.



Dangers of visible light: ﻿blindness

<span style="color: #ff0000; font-family: 'Comic Sans MS',cursive; font-size: 120%;">Checkout this webpage. [|Don't look at the sun! Ever!]

__**<span style="color: #0000ff; font-family: 'Comic Sans MS',cursive; font-size: 150%;">Ultraviolet Waves. <span style="color: #000000; font-family: Arial,Helvetica,sans-serif;">﻿ **__

__**<span style="color: #008000; font-family: Arial,Helvetica,sans-serif; font-size: 120%;">Uses: **__ <span style="font-family: Arial,Helvetica,sans-serif;">﻿include security marking, florescent lamps, detecting forged bank notes and disinfecting water.




 * Ultraviolet germicidal irradiation** (**UVGI**) is a sterilisation method that uses ultraviolet (UV) light at sufficiently short wavelength to break down micro-organisms. It is effective in damaging the DNA within the cells, this removes the ability for the cell replicate and therefore kills the micro-organism.

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__** Dangers of Ultraviolet rays: **__ include damage to surface cells and eyes, leading to skin cancer and eye conditions.

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<span style="color: #0000ff; font-family: 'Comic Sans MS',cursive; font-size: 150%;">__**X-rays.**__


 * Uses: ** ﻿include observing the internal structure objects, airport security scanners and medical x-rays.

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__**Dangers of X-rays:**__ ﻿ include mutation or damage to the cells in the body. High doses can kill normal cells, and lower doses can cause cancer through the destruction or mutation of cells.

Read this newspaper article [|Dental X-ray link to thyroid cancer.]

__<span style="color: #0000ff; font-family: 'Comic Sans MS',cursive; font-size: 150%;">**Gamma rays.** __


 * <span style="color: #008080; font-family: Arial,Helvetica,sans-serif; font-size: 130%;">﻿ ﻿ Uses: ** <span style="font-family: Arial,Helvetica,sans-serif;">﻿ ﻿ ﻿ ﻿include the detection of cancer and its treatment, killing bacteria on food, sterilising medical equipment.



<span style="color: #000000; font-family: Arial,Helvetica,sans-serif;">Food may be sterilised using gamma radiation in order to increase its shelf-life. The gamma rays kill micro-organisms, such as bacteria, that may be harmful to humans.

__**Detection and the treatment of cancer.**__

<span style="color: #000000; font-family: Arial,Helvetica,sans-serif;">

The picture on the left shows the image from a 'gamma camera' immediately after a human has been injected with Technetium-99. The picture on the right shows an image six hours later. You can see cancerous cells as a yellow glow (lung cancer).

**Dangers of Gamma Rays:** High dose can kill normal cells, and lower doses can cause cancer through the destruction or mutation of cells.