Photocopier

The Copying Machine

Chester Carlson was the inventor of photocopying.
Copying machines works on the electrostatic process called Xerography. Photocopiers are used in businesses, studying, in homes etc. Its purpose is to reproduce documents, pictures and other items.

Have you ever wondered about how the photocopier machines, which are so convenient to use,works?

If not, let us have a glimpse at the working of the machine.

 The copying machine works on the basic principles of attraction of positive and negative charges. Here we will see four steps of its working,

 

1]Charging

The machine has in it attached a cylindrical drum called photoreceptor which is light sensitive. In the first place, the photo receptor is charged negatively using a wire with high voltage. The photo receptor is coated with photo conductive material called Selenium. Selenium is a material which behaves as an insulator in dark and as a conductor when exposed to light.

Cadmium sulphide, zinc oxide and organic polymers are also used.

2] Exposure

A bright light is illuminated on the original document which is to be copied. The white surface of this document reflects the white light on the photo receptor. The area of the photo receptor which is exposed to white light from the white paper of the original document is charged positively and the left out dark portion of the photo receptor is charged negatively. This dark portion corresponds to the black portion of the original document which was reflected.

3] Developing

The powder which is used to create image is called toner. The toner ranges about five to ten micrometers in diameter. To create the image on the photo receptor, the toner is transported on it. Now this toner is positively charged so it sticks to the negatively charged portion of the photo receptor which is not exposed to light.
This way the pattern is created on the photo receptor.

 

4]Transferring

Now to create the copy of the image on the paper, the photo receptor with the toner which is sticked to it is brought in contact with the paper. The paper is highly negatively charged in order to subdue the adhesive forces of the powder.

5] Fusing

In transferring, the paper was patterned with the powder so there are chances of some particles of toner to come off the paper. So, in order to prevent this, the paper is passed through a pair of heated rollers by applying high pressure so that it melts the toner.

In this way, toner is permanently bonded to the paper and the copying is completed.

Advantages & Disadvantages

The copies are of good quality and are exact copies of the original document. Nowadays, the photocopiers have become light weight and easier to handle. Buying one copier, you can work in-house. You can go green, as you can also use recycled papers. Recycling of waste toner is also practiced by most manufacturers.

However using photocopier has certain disadvantages too.

There are things that has to be replaced regularly , like the ink, paper and thermal film are some examples.

Health hazards

Photocopiers produce small amounts of ozone gas too. This odorous gas is irritating to eyes and is harmful to the throat and lungs. The main ingredient in the toner is carbon black which of course is not a good thing.

Taking precautions while using a photocopier machine like choosing a low emission power photocopiers, keep your distance, replace your photocopier if it gets too old, maintain your machine well etc can help you keep your health quite well.

 

 

What is a Wave?

 
 

Let us take one example, if you drop a pebble in still water, the water surface gets disturbed. This disturbance is not confined to one place but here the particles of water are moving up and down at their respective positions. But still there is something which moves outward, we call it a wave...

To make it simple, wave is a disturbance from equilibrium position which travels, but more substantially particles do not travel, it just oscillates about their mean positions. Primarily, waves are of two types:

 

                                                            Wave Diagram

1] Mechanical waves

Mechanical waves require a medium to transport their energy from one location to another. Sound waves require a medium(air) in order to propagate, thus sound waves are mechanical waves also since sound waves are incapable of traveling through vacuum. Waves on a string, waves in air column etc are called mechanical waves.

 

→ Types of mechanical waves:

 

a. Longitudinal wave

→The vibration of the particle is in the same direction as that of the direction of propagation of wave.

Example: sound wave, pressure waves etc are longitudinal waves.

 

b. Transverse wave

→The vibration of the particle is in the direction opposite to the direction of propagation of wave.

Example: Light wave, seismic waves, vibration in a string etc are transverse waves.

 

c. Surface wave

→A surface wave is something which travels along the surface of a medium. This waves usually occurs at the boundary of the two media.

Example: Waves in ocean is the example of such type of waves.

 

 

2] Non-mechanical waves

Waves which does not require a medium to transport their energy from one location to another are called non mechanical waves.

Example: Electromagnetic waves are non mechanical waves since it does not require any medium to propagate.Electromagnetic waves are waves which are produced due to the periodic vibration of two mutually perpendicular electric and magnetic fields.

Heinrich Rudolf Hertz proved the existence of the electromagnetic waves.

How is the temperature of the sun measured?

 After reading this question you might think about measuring sun’s temperature probably by sending some sort space probe with thermometer near sun which would do that, but we all know that's, not possible of course. 

So how do we do that. 

 

Let’s look at something interesting. 

 

Some of you might be aware about what radiation is, but there’s  nothing to worry about even if you don’t ,understand that radiation in simple words is defined as the transmission of energy from a body in the form of waves or particles. This can encompass anything from dangerous radiation created by a nuclear power plant to the harmless light created by a flashlight.There is a term called black body radiation, which means that a body which absorbs (and emits) all wavelengths of light and so appears black. 

 

Coming back to our question, how is temperature of the sun measured and the answer is by Wien’s Displacement Law or Stefan’s Boltzmann 

relation?

 

Wien’s displacement law  states that the wavelength for which the emission power of a black body is maximum is inversely proportional to the absolute temperature of the black body. Wien’s Displacement law equation is useful to find the temperatures of hot radiant bodies such as stars and used for finding the temperature of any radiant object which is far above that of its surroundings.According to Wien’s Displacement Law, 

λ(max) ∝ 1/T   

 

λ=b/T 

 

 

where, λ  is the wavelength,T is the temperature and 

 

b is Stefan Boltzmann constant whose value is 

 

2.898×10−3 mK. 

 

 

The wavelength of the peak of the black body 

 

radiation curve decreases in a linear fashion as the 

 

temperature is increased.

 

This linear variation is not evident in this kind of 

 

plot since the intensity increases with the fourth 

 

power of the temperature according to Stefan 

 

Boltzmann Law.

 

 

Since the temperature of the sun is high, its wavelength is minimum according to Wein’s Displacement Law so with the help of intensity of radiation we can calculate the temperature.

 

The sun is considered as a black body. Since the

 

light from the sun, we have seen from the surface 

 

has had nearly the spectrum of a black body. It 

 

implies that  emissivity(e) of the sun is 1(emissivity 

 

of black body is always 1).

 

Radiation spread out by the sun per square meter is 

 

estimated to be, I=1.36kW/m^2 

The radius of the sun is 7.0×10^5 km.

According to Stefan’s Boltzmann law, Q=eσ AT^4

Q is the power radiated by thermally emitting 

 

object, 4π d^2I

E is the emissivity power which is 1, σ is a constant, 

 

5.67 ×10^-8W/m^2K^4

A is the surface area(calculated from the radius) of 

 

the sun and

T is temperature of the sun.

Substituting the values by solving for T we get the 

 

value to be approximately 5760K(Kelvin)

T is approximately equal to 5800K