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Choosing a light source

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Task 1image62.pngimage10.pngimage01.png

As a part of this tasks, I will conduct a survey to show the way in which light is produced in the following types of lights;-

  • Domestic
  • Industrial/commercial
  • Outdoor


For the domestic lights, I have used house hold light bulbs which are made from a tungsten wire. the tungsten wire is placed inside a glass so that when it is heated, it does not react with oxygen to produce a oxide. The diagram below shows a tungsten light bulb.    






the voltage that is passed though the power supply goes to the tungsten wire and interferes with the atomic structure of the electrons on the atom of the tungsten. this is because the voltage is energy, and this energy moves the electrons for the orbital of the nucleus of the atom. If one of the electrons in the shells of the atom move out of place, then this must be replaced by another one straight away to keep the orbital of the electrons around the nucleus right. So to do this, one of the electrons from the outer shell of the atom jumps in to the place of the atom that was knocked out by the voltage. In doing so, a photon of energy is passed out. This photon is the light we see when we turn on a bulb.  

The tungsten metal is a good metal to be used for this kind of job. This is because tungsten has a high atomic number. This means that there are more shells of electrons. More electrons would mean that more photons can be produced from this metal which make it idle and give it a high melting point.

The tungsten has to be placed in a glass container.

...read more.


The diffraction grating has many slits in it. this could be as many as 10,000 per cm. when a light source is passed through the diffraction grating,  a pattern of interference fringes is seen on the other side of the grating. When a monochromatic light (single wavelength) light is passed through the grating at 90o form the grating, on the other side of the grating, a interference fringes are formed. This has been shown in the diagram below.    image22.pngimage21.pngimage24.pngimage23.pngimage25.pngimage20.png

Measurements that need to be taken to work out the wavelength of the wave  

The formula below is the general formula that can be rearranged to work out the wavelength of the light.

Order of  angular separation x wavelength (γ) = distance between slits (d) x angle(sin θ)

The formula can be rearranged to work out the wavelength of the light that passes through the diffraction grating. This has been shown below.

Wavelength(γ) =distance between slits (d) x angle(sin θ)

                     Order of  angular separation (n)

γ = d sin θ


from looking at this formula, I can see that I would need to take the following readings to be able to work out the wavelength of the sodium light.

  • Distance between the slits on the diffraction grating. This depends on the grating that is used.  
  • The angle at which the telescope is placed for the grating. This is found by looking a the venire scale.
  • Order of the angular separation of the  interference fringes. This is found by observation.  

Working out the wavelength of a sodium light source.

For this experiment, I used a diffraction grating which had 1092 slits per centimetre. To work out the distance between each slot, I must divide 0.01m by 1092 as the value for d must be in metres . this Has been done below.

Value for d (distance between slits)

  0.01    .image26.pngimage27.png


...read more.


A halogen light is brighter then normal light bulbs.

Gives very good colour rendering as it produces a whit light.

Halogen light bulbs provide full light intensity when it is turned on. It does not need time to warm up.  

Disadvantages :-

Halogen light bulbs operate at higher temperatures then normal light bulbs. This means that there is a bigger risk of getting burns from the bulb

Halogen light bulbs can brake or even explode as they are made from glass. If the glass is hot, it can start a fire.

If shielding brakes, then it exposes ultraviolet light to surrounding.

They cost more then normal light bulbs

Halogen light bulbs above the power of 300 Watts have a higher risk of starting a fire. For this reason, they are not allowed for dormitory uses

solar yard lamp


A solar yard lamp uses a solar panel to charge the battery at day time and then at night time, the charged battery is used to power a tungsten light bulb.


The good thing about a solar powered produced is that there is no electric used as the power is supplied by the sun. This means that there is no bill.

There is no wires that are needed for the light. This makes it less fiddly.

The light atomically turns off and on. This means that when the light is needed, it is there with out having to turn it on.

It makes the out side of your house bright and makes it look nice.


They cost a lot to buy compared to other electric powered light bulbs.

The light can only be used in a place where the sun will reach it as it will not charge if the sun does not hit the solar panel

The light will not work as will in short days like in winter. This is because the solar panels will not get enough light to charge.

The solar panels are sanative, they can brake.

...read more.

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