Q. Why are tallest structures in a locality most likely to be struck by lightning?
A. When charged clouds pass over the building, opposite charges are induced on it thus attracting the charges of clouds. The tallest building being nearer to the clouds, there is greater possibility for the lightning discharge to take place between the building and the cloud.
Q. Why is the filament in an electric lamp not burnt up although its temperature is about 2700°C when it glows ?
A. The presence of oxygen or air is ‘ essential for the process of combustion to take place. To avoid the process of combustion, the air inside the bulb is removed by evacuation or alternatively the bulb is filled with an inert gas like argon or helium.
Q. Explain the quantum theory.
A. It is a theory which is based on Max Planck’s radiation law. The concept of discontinuity of energy was introduced by it. According to this theory, changes of energy in atoms and molecules occur only in discrete quantities, each an integral multiple of a fundamental quantity. The fundamental quantity is generally referred to as quantum.
Q. What is Mach I speed of an aeroplane?
A. 760 miles per hour.
Q. What fact or law is associated with the rise of balloons in the air?
A. This is in accordance with Archimedes’ principle. Balloons are filled with some gas (hydrogen or helium) lighter than air. A balloon filled with the gas occupies a large volume. The upthrust produced by the displaced air is much greater than the weight of balloon. Hence, it rises in the air.