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Overview         (For age - group : 11 - 16 )

How can a piece of plastic save lives. Total internal reflection here scores over reflection . Night reflectors do not use any power but light up as soon as light hits them but they do not produce glare, as any mirror would, but glow in the light, how do they manage that, learn more by looking at this educational science animation

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Bicycle or night Reflector:
Category : Science > Physics
Type : Animation
Duration : 6 minutes

  1. Why a mirror cannot be used in place of a plastic reflector
  2. Construction of a reflector
  3. How total internal reflection takes place inside the reflector ?
  4. How is the light reflected back in the direction of incidence ?

Explanatory notes section contains :

  • Can a reflector be used for measuring the distance of moon from earth?
  • What are the shortcomings of a reflector ?

night reflectors glow when any light falls on them Night or bicycle reflector
Night reflectors glow when any light falls on them
Night or bicycle reflector
The ray of light incident on the reflector are sent back in the same direction Total internal reflection takes place inside a reflector
The ray of light incident on the reflector are sent back in the same direction
Total internal reflection takes place inside a reflector
Details of the animation/ movie /software

The red plastic reflector on the back of a bicycle is shaped so that light from a cars headlight hits the front surface at a very small angle of incidence. But the back of the plastic is angled. The light hits this surface at a high angle of incidence. Total internal reflection occurs. All the light bounces back , and is returned in the direction from which it came. No matter in which direction the light is incident on the reflector, it always retraces its path. So car drivers see the reflection of their own headlights in the reflector.

The same principle is used in automobile reflectors.

The question that can arise out the concept of reflectors is : Why cant a mirror be used in place of reflectors, the answer is that mirror does not reflect back the light in the same direction as the source so the source will not be able to see the reflector or the object like car, mototrcycle that has the refelctor mounted on it .

The concept of the reflecting back along the same path is illustrated in the aninmation through a animated ray diagram.

Explanation of the same phenomenon can be applied to the Questions like
Can a reflector be used for measuring the distance of moon from earth
What are the shortcoming of a reflector

These questions are answered in the explanatory section of the animation

If you are still unclear about the concepts, please refer the animation.

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Q5: how much do I have in my account Anyebe david 22/9/2007
Ans: Even though you have registered and created an account on our site but you have neither purchased a subscription or any product hence the account is blank right now , after you purchase some products or subscribe to a package, your account will be updated to show the number of hours you can use to view our animations online or products you can download to your computer.
Q6: sir could you suggest name of some sites. sumeet 14/6/2007
Ans: Since you are looking for punches for reflector injection moulding, China is the king of plastic moulding and that is where you can contact the manufacturers, we are giving some of the sites we came across, you can also use google keywords reflector , punch , mould to get more info.,, Hexian Shunjay Safety Products Company Limited (plese google it),
Q7: cycle reflectors are moulded from punch & cavity injection moulding dies,my ? is how are punches made.? sumeet 20/5/2007
Ans: Sumeet we do not have knowledge about the material of the punch, maybe you can refer to reflector manufacturers site.
Q8: how are reflector prism pins made? sumeet 13/5/2007
Ans: Can you be more specific as to which instrument does your question refer to, for night reflectors or some other one
Q9: why polycarbonate is used and not acrylic even though PMMA has better clearity? sumeet 2/1/2007
Ans: Though both are thermoplastics. Polycarbonate is about 30 times stronger than acrylic. Light transmittance is comparable (acrylic 92% and polycarbonate 86-89%), less brittle, softer, more impact resistant therefore ideal for outdoor usage ( Acrylic shatters on impact) less prone to cracking when being machined. Polycarbonates may be exposed to a variety of materials without corrosion -example ethyl alcohol, detergents, fruit syrup, HCl acid (20%), H2SO4acid (50%), fruit juices, and water.
Q10: reflector is made from which plastic and why sumeet 1/12/2006
Ans: They are made from injection moulded polycarbonate or polyvinyl - because it is cheap and durable. Good quality reflectors meet EN13356(EN471) quality standards.

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