Practice MCQ Questions and answers on Physics-GK

When the wire is stretched to double the length , the area of cross section gets reduced to half. So when the wire is stretched, the resistance multiplies by four times.

The filament of an electric bulb is made of tungsten because it has some amazing properties including the highest melting point (3422^oC), lowest vapor pressure, and greatest tensile strength out of all the metals.

A compact fluorescent lamp (CFL), also called compact fluorescent light, energy-saving light and compact fluorescent tube, is a fluorescent lamp designed to replace an incandescent light bulb; some types fit into light fixtures designed for incandescent bulbs.

When connected in series, the voltages divide in them in the ratio of their resistances. The voltage of 440 V devides in such a way that voltage across 25 w bulb will be more than 220 V. Hence 25 w bulb will fuse.

1 WH (Watt hour) = 3600 joules

The electrical domestic tube light gives white fluorescent light because of falling of ultra violet rays on the white inner coating of the tube. The ultraviolet rays have high frequency and shorter wavelength are converted to visible white light with lower frequency and greater wave length.

Electricity is measured in units of power called Watts, named to honour James Watt, the inventor of the steam engine.

The device used to change the speed of an electric fan is regulator.

Most heating elements use Nichrome 80/20 (80% nickel, 20% chromium) wire, ribbon, or strip. Nichrome 80/20 is an ideal material, because it has relatively high resistance and forms an adherent layer of chromium oxide when it is heated for the first time. Material beneath this layer will not oxidize, preventing the wire from breaking or burning out.
Hence, Nichrome is used as heating elements.

At high operating temperatures, tungsten evaporates from the filament and gradually forms a gray film on the inside of the bulb. The inert gas atoms collide with the evaporating tungsten, causing some of the tungsten atoms to return to the filament.