Physics Quiz 4

When the two ice cubes are pressed together, melting point of ice is lowered, so they melt to form a thin layer of water (between them). On releasing the pressure, the water formed freezes because decrease in pressure raises the freezing point. Hence they unite to form one cube. When water freezes, water molecules form a crystalline structure maintained by hydrogen bonding.

During washing of clothes, we use indigo due to its proper pigmental composition. The combination of yellow and blue colours gives white colour. Hence we add blue indigo to remove yellow tint from the white clothes.

Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Humans can detect sounds in a frequency range from about 20 Hz to 20 kHz. The frequency of ultrasound waves is above 20 kHz.

Electrostatic precipitators are used for air pollution control, particularly for removing harmful particulate matter from waste gases at industrial facilities and power-generating stations.

The apparent weight of a man in a lift is less than the real weight when the lift is going down with an acceleration. When a lift accelerates upwards, the apparent weight of the person inside it increases; and when a lift accelerates downwards, the apparent weight of the person inside it decreases.

The main attribute common to all lightning rods is that they are all made of conductive materials, such as copper and aluminium. Copper and its alloys are the most common materials used in lightning protection.

Prism is used to split white light into different colours. Prisms are specially shaped so that light passing through them bends. Some colours bend more than others as they pass through the prism, so they split apart.

Tungsten metal is used exclusively for making the filament of electric bulbs because it has a very high melting point. Due to its high melting point, the tungsten filament can be kept white-hot without melting away.

Frequency determines colour, but wavelength is the easier thing to measure. These wavelengths range from 700 nm at the red end of the spectrum to 400 nm at the violet end. Visible light waves are the only electromagnetic waves we can see.

Complementary colours are pairs of colours which, when combined or mixed, cancel each other out by producing white or black. Examples of complementary colour combinations are: Red and green; yellow and blue (purple).