Category Science

  Chronometers are used to determine the speed of the vehicle with a hand held stopwatch. No radar, no loop just a plain and simple digital stop watch, and two points of a known distance apart. Start and stop switches are to be manually actuated when the vehicle crosses the points.

The speed will be displayed instantly. The second method is by using a Piezo Sensors, this method uses set of 3 rubber strips with a specific distance apart are build across the road or buried in the road. The time between compressions is measured to give the resulting speed of the vehicle. If the speed exceeds the camera associated with the system will photograph the vehicle.

In another method two beams of invisible infrared beams are emitted across the given traffic lane. The elector optic head directs the beams to two retro-reflectors mounted on the road surface.

            Every vehicle passing between the electro optic head and the reflectors breaks the beams and triggers the unit computer to measure the speed. If a vehicle exceeds speed limit, the high-resolution camera photographs the front or rear of the vehicle including its license plate.

            In another method, infra red diodes are pulsed at certain frequencies and to create radar beams. This beam is emitted via parabolic reflector at 15 degree spread and directed towards the traffic. The emitters are shielded to prevent external interference.

            They normally use K band in a frequency 24GHZ. The associated computer will measure speed and triggers camera to capture the image of erring vehicles.

            This works on the phenomenon of Doppler Effect. When a sound source and an observer are in relative motion with respect to the medium in which the waves propagate, the frequency of waves observed is different from the frequency of sound emitted by the source.

            This phenomenon is called Doppler Effect. This is due to the wave nature of sound propagation.    The principle of Doppler Effect is used to detect the speed of automobiles by traffic police. An electromagnetic wave of constant frequency is emitted by a source attached to the police van. The wave is reflected by the moving vehicle which in turn acts as a moving source.

               

 

            Stationary objects experience only the gravitational force. Such objects can be balanced only when the line of action (line connecting the centre of gravity of the object towards the earth) touches the ground at a point within the base of the object. If the base area is large, slight deviations due to external forces such as the wind will not push this point out of the base.

    So it is easy to balance such objects. In the case of a two wheeler, the base is very narrow, almost a line connecting the two points where the two wheels touch the ground. Hence any slight disturbance will push the line of action outside the base area leading to difficulty in balancing.

            During motion the situation is entirely different. In addition to gravity there is another force exerted by the engine. It acts in the forward direction.

            The resultant of these two forces is in the forward direction and so the vehicle moves forward independent of where the line of action cuts the ground. Hence it is easier to balance a moving vehicle.

New vessels are rubbed on the surface with an abrasive powder. This makes the surface almost uniformly leveled.

Almost all the light falling on the buffed surface gets reflected uniformly along certain directions depending on the shape of the vessel. This makes them shine.

  Upon continuous use, scratches are formed and so the surface becomes rough. Hence, the light falling on the surface is scattered randomly all around. Hence the reflectively of the surface is not as good as it was before. Dirt accumulating on the scratches, corrosion and oxidation of the metal surface dull the vessels further.

            The surface of any metal when scrubbed and polished would have a shinning appearance. This is a characteristic property of metal and is due to reflection of light.

            When exposed to air and moisture, most metals react with oxygen, carbon dioxide and moisture. Iron vessels rust and others such as copper and aluminum tarnish. When such vessels are used for cooking, this process gets quickened; aluminum gets coated with its oxide and becomes dull. Copper gets covered with its basic carbonate resulting in a green colour.

            We are familiar with an age old practice of cleaning such vessels with tamarind.

Mild organic acids present in such fruits and vegetables dissolve the coating and restore the sheen. Washing powders which are alkaline also aid in dissolving the dull coat.

Metallic tin is resistant to many of these reactions. That is it used to ‘tin’ copper vessels. Stainless steel does not get tarnished due to the presence of chromium in it.

Even silver vessels get tarnished due to the trace amounts of hydrogen sulphide present in the atmosphere. Such vessels also require polishing in this case with the more poisonous cyanides!!!

It is true that gas filled bulbs (mercury or sodium) or tube lights emit more light compared to ordinary filament bulbs for the same power input. Basically when an electric current (flow of electrons) passes through any ordinary material both heat and light energy are developed in the body. In filament bulbs the current passes through a thin wire made of tungsten.

Because of its material structure more light is generated than heat. However a part of the energy (power) is dissipated as heat in the body. Also the light emitted is limited by the surface of emission and the length of the tungsten wire.

In the case of bulbs filled with mercury vapour or sodium vapour the electrons move from cathode to anode through the vapour.  These gas molecules are good conductors of electrons and the electrons passing through these molecules emit light. Comparatively lesser power is dissipated as heat. Also the electrons passing through those freely suspended molecules in three dimensions have greater volume and space compared to the electrodes through the filament, leading to higher intensity of light.

 

Air surrounding the conductors of a high voltage overhead transmission line is normally an insulator. But at extra high voltages (66,000 volts and above), the air in close proximity to the conductor tends to break down under the voltage stress, along the length of the conductor and itself becomes a conductor. This is known as corona effect. Corona appears in two forms, visible corona as a bluish violet light and audible corona as a hum. Audible corona is common. Visual corona requires a higher voltage stress.

   The atomic mass is concentrated in the nucleus, the electrons going round it contributing very little to the mass of the nucleus. The positive charge on the nucleus equals the charge on the electron. All nuclei other than hydrogen are made of protons which were brought together against the Columbian force of repulsion at very high temperatures.

 The formation of nuclei in nature suggests the presence of a strong force which is charge independent. The mass of all nuclei is found to be approximately twice the number of charge on the nucleus except in very heavy nuclei like uranium where it is about 2.6 times the charge.

 As the charge on the nucleus is equal to the number of electrons, there should be twice as much matter in the nucleus as is needed to explain the charge. It is possible only if the nucleus is made of particles with no charge but mass nearly equal to that of a proton.

 In 1932, James Chadwick observed that when beryllium was bombarded by alpha particles radiation which were neutral in charge were emitted.

 He repeated the experiment with different materials to establish the fact that the mass of the particles was about 1 mass unit and charge to be neutral. In 1935 Chadwick was given the Nobel Prize in Physics for this great discovery, seeing the missing part of the nucleus!