My Science School

 In filament lamps a good part of the electrical energy is used up in heating the filament which in turn glows throwing light around. While in fluorescent tubes light is produced by electrical discharge in a glass tube, the inside of which is coated with a fluorescent material. The filaments at the two ends are used only to start the discharge. The discharge passing through vapours of mercury produce UV radiations which excites the fluorescent coating producing visible light. Since very little heating is involved in the process and most of the electrical energy is used in producing light, fluorescent tubes consume less power than filament lamps.

            Milk is a fine suspension of fat and protein globules in a watery liquid containing milk sugar (lactose) and other dissolved substances. Normally the fat is dispersed uniformly in the form of fine droplets and hence remains as an emulsion. But when milk is heated these fine droplets tend to raise up and at temperature of about  form a thick layer of cream on the surface. When milk comes to boiling, bubbles of steam formed at the bottom of the vessel rise up and force the thick creamy layer upwards causing the milk to spill.

                                    

  Ballpoint pens have a tiny ball made of brass, steel or tungsten carbide as their writing tip. The ball is fitted into a socket and is connected to the ink reservoir by a thin tube. When we write on paper, the ball rolls due to friction between the ball and the paper. This rotating movement allows the thick ink to flow out slowly leaving a mark on the paper.

  When drawn over a smooth surface such as glass or plastic there is little friction between the ball and the surface. The ball is unable to rotate and, as a result, the ink cannot flow out. Hence we cannot write on smooth surfaces with a ballpoint pen.

     A petrol engine can’t be run with diesel or a diesel engine run with petrol because the engines and their fuels are made for each other. In a petrol engine, for instance, a spark ignites a mixture of petrol vapours and air. This is possible because petrol is highly volatile and easily vaporuizes. Diesel cannot take the place of petrol here because it is less volatile. A different strategy is used in diesel engines. Here, the air is made hot by first compressing it. Diesel is then squirted into the hot air and it burns. Besides, the compression ratio, the difference between the pressure of the fully compressed fuel mixture and atmospheric pressure is much higher in a diesel engine. That is why; diesel cannot be used in place f petrol or vice versa.

When an empty metal vessel is struck, the entire surface of the vessel is set into vibration. The air in contact with the vessel is also set into vibration producing sound of high intensity. If the vessel is partly filled, the surface area of the vessel remaining free to vibrate becomes greatly reduced. Since the total area of air that is set into vibration by the vibrating surface of the vessel also becomes much smaller than in an empty vessel, the intensity of sound also gets reduced.

   The earthing of electrical appliances is done as a safety measure. Most of the non-current-carrying metallic parts of an electrical appliance are well insulated and safe to use, but in a faulty appliance current can pass through even these insulated parts and pose a risk to the life of the user. This is because the human body allows an easy flow of electricity through itself to ground. The earthing of the appliances prevents this risk as the earth wire offers a still easier path compared to the human body to the flow of leaking current to ground, thus making the appliance safe to use.

     It is easier to balance a long pole on the palm than a short stick because of the higher position of the centre of gravity in the former which normally lies near the middle. For balancing a long pole by holding it upright on its end on our palm what we try to do is to keep its centre of gravity right above the base. As long as the centre of gravity remains straight above the base, the stick remains balanced. But being unstable, it tends to fall and the centre of gravity moves away from the vertical. With a long pole we get sufficient time to move our hand to bring its base directly below its centre of gravity thus restoring balance. But with a short stick we hardly get any time to move our palm to restore the balance and the stick falls down.

            We need to wear dark sunglasses in snow-covered areas to prevent damage to our eyes from bright light. Normally our eyebrows cut off the glare from the sky on a bright sunny day. In snow-covered areas, however, the white snow on the ground reflects back most of the sunlight producing a glare of very high intensity. Exposure to such bright light is capable of causing snow-blindness or temporary loss of sight. The use of sunglasses cuts down the glare and helps to prevent damage to our eyes.

A kite flies better without wobbling, spinning or diving if it can keep itself inclined at a specific angle against the blowing wind. This creates a difference in the air-pressure around the kite in such a way that the kite is lifted up. The tail helps a kite in keeping its angle of inclination stable by pulling down its lower tip. Without the tail, wind blowing against the kite and the lift-force generated in turn would send a conventional kite into a tail-spin. Box-kites, however, do not need a tail to stabilize as they do not need to maintain a constant facing angle against the wind to generate the lift. The air swirling through and about a box-kite creates all the pressure differences required to lift up.

            The seconds hand of both quartz and spring watches move in jerks. Only the movement is much more discernible in quartz watches. In spring watches the movement of the seconds hand is guided by the oscillations of the balance-wheel driven by the hair spring. Since the balance wheel oscillates several times a second, the seconds hand in a spring watch appears to move smoothly as the small jerks are almost non-discernible. On the other hand, in quartz watches, the battery powers a stepping motor that moves the second hand in a single step once every second, which can be quite easily made out and the movement appears jerky.

        Another reason for the illusion is the difference in the amount of angular movement each jerk produces in a second hand. In spring watches it is only  whereas in quartz watches it moves by as much as  in a single step.

                                     

   Soaps are salts of fatty acids. Common soaps are water soluble sodium and potassium salts of fatty acids. Soap cannot form lather unless it dissolves in water. Hard water does not dissolve soap because the calcium and magnesium salts present in it produce insoluble substances by reacting with soap. These insoluble substances separate out as scum and reduce the effectiveness of the soap as a cleansing agent.