Friday, 1 July 2011

Why are aeroplanes not affected by lightning?

Clouds are made of water droplets and dust in the atmosphere at altitudes of 1 to 16 km.While traveling through air,due to friction,the water droplets get electrically charged.Lightning occurs due to sparking between oppositely charged clouds-a high voltage spark rushes towards the ground(at zero potential) through moisture-filled air.
If any ground based structure is on the path of the spark,the top of that structure is excited to a high electrical potential while its bottom (in contact with the ground) remains at zero potential.This high potentail difference sets a very high current in the structure causing sudden heat generation in the material and destruction.But in flying aeroplanes,there is nothing like a ground point which remains always at zero voltage.

Hence even if hit by a lightning,the plane's entire surface acquires the same high potential and due to lack of potential difference there is no current and hence no destruction.

What constitutes bulllet-proof glass ?

High-strength ceramics such as silicon nitride,dual hardness steel and layers of heavy nylon fabric make a bullet-proof glass impervious to bullets.The hard ceramic stops the bullet abruptly,dissipates its energy as it destroys the first layers of the glass at the point of impact and entangles it in a coarse mesh.

A textile bullet-proof vest is fashioned of 16-24 layers of nylon cloth of heavy weave,the layers stitched together like a quiet.Such vests or full-torso protectors can be worn undetected under regular clothing.A vest of 16 layers will stop regular handgun and sub machine-gun bullets,those of 24 layers will stop the powerful magnum bullets from the same weapons.

Why do birds fly in formation shaped like the alphabet 'V'?Which bird works the hardest in such a formation and why?

The bird in the lead (at the forward point of the 'V' formation ) works the hardest by being the first to 'break through' the air,which offers resistance to its flight.Just as a boat leaves a V-shaped wake of smoother water behind it(actually the lead bird creates a trail of air turbulence that helps lift along the V-shaped direction),and it is a bit easier for the other birds to fly in the wake of the lead bird.

If you watch a V-formation carefully,you'll notice that the lead bird does not stay in that position for a very long and will drop back into the formation,while another,not as tired bird takes the lead,breaking through the air first.

How does remote control in TV works?

In earliar days,remote were based on ultrasonics(sound frequency above the audible range of frequencies).The controlling circuitry included a hand held transmitter (that transmits ultrasound) and a TV-based receiver circuit.Electronic filters and stepper motors were used to allow/select certain frequencies and perform various functions depending on the key pressed.
But the  recent remote controls use infra-red(IR) rays and a special binary (0 and 1) coding menhanism.The code,intensity and wavelength of IR wave,help to select different functions.Depending on the key pressed,a signal is sent out by IR source,say,an injection laser diode(ILD).It generates a code in a parallel format.This is converted to a series format by a shift register.This signal is received by photo-sensitive devices such as an avalanche photo diode at the receiver.

Here another shift register is used to convert the code back to a parallel form.This operates a one-of-n decoder,which selects one function from a set of 'n' predefined functions and executes it.