Question corner

Blinking our eyes

QUESTION: Why do we blink our eyes?

P. V. Srinivasan, Chennai

ANSWER: Blinking is a protective mechanism of the eyelids sweeping across the eye. Basically, it is of two types.

Reflex blinking: Sudden closure of the eyelids in an attempt to dislodge an object which has activated signals from cornea or conjunctiva. Visual stimuli like, a small body moving rapidly towards the eye or an intense flash of light, stimulation of skin around the eye and sudden bursts of sound can also initiate this reflex.

These stimuli mediate in the brainstem, which, via the facial nerve signals the contraction of the ortricularis oculi muscle closing the eyelids. These blinks last for about 150-200 milliseconds (ms). and have large amplitude, covering the pupil in the process of the closure. It is usually accompanied by lacrineation initiated by parasympathetic stimulation.

Regular spontaneous blinking: Occurs every 3-7 seconds, about 12 every minute. These blinks are responsible for spreading and draining of tears over the cornea. Keeping the cornea moist protects it from infection and ulceration.

The upper eyelid wipes down the tears and the lower medically, thus dislodging minute particles along with tears to the medial corner of the eye. These blinks last for 250-300 ms and have a smaller amplitude than the reflex type.

G. R. Kiran, Prashanthi Nilayam, A.P.

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Using diesel for motorbikes

QUESTION: Why do two wheelers not use diesel?

R.P.Rammohan, Hyderabad

ANSWER: The problem lies in power to weight ratio of the bike. Bikes that use diesel as fuel are heavy in size. The power output from the diesel engine is high and more over noise and vibrations are at a high level, prohibiting them in common use.

Diesel cannot be used with 50, 100 and 150 cc engines, because of high power output. Diesel engine is a compression ignition engine where diesel injected into a cylinder of high pressure and temperature compressed air, under a very high pressure. Atomized diesel particles come through a tiny hole of fuel injection nozzle burn and release mechanical power output. Design and manufacturing of such minute mechanical parts, withstanding high temperature and pressure is not cost effective.

And usage of diesel demands heavier heavier construction of all structural parts to endure high vibrations. The cost is also high. If the engine is not serviced properly and periodically the pollutants level emitted will be very high when compared to petrol engines. At present only Enfield India Manufactuers motorbikes which use diesel as fuel.

R. Senthil Kumar, Pudukottai, T.N.

This Week's Questions

In what direction will the compass point when it is taken to North/ South pole?

V.Jayaraman, Erode, T.N.

Will aircraft get affected if they happen to fly over the epicentre during the time of earthquake?

G.Rajaram Gnanavel, Villipuram, T.N.

What is a speech synthesiser? How does it work?

K.P.Kurian, Kottayam, Kerala

Why do people never get cancer in the heart?

V.Priya, Chennai

What is sponge iron? How is it manufactured?

M.Elayaperumal, Trichy, T.N.

How do dust particles accumulate on the wings of a fan?

Prabu Sudhakar, Kolathur, T.N.

What is the difference in energy content of raw and boiled rice?

R.V.Mukundan, Chennai

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