Physics

In SONAR ultrasonic wave is used.

Ferromagnetic materials are mainly solid materials (eg. Iron, cobalt, nickel etc). And this property of ferromagnetism is only observed in the solid materials but not in the liquid or gaseous materials.

The raise of oil up the wick in a lamp is an example of capillary action where adhesive forces are greater than cohesive forces.

X – rays, infrared, visible, microwave

The time period of a pendulum is directly proportional to the square root of its length. So, if the length increases, its time period also increase. It means that it takes longer to complete one oscillation. So when its length is halved, its time period is decreased by a factor of 2.

Siphon is a tube bent to form two legs of unequal length by which a liquid can be transferred from a reservoir and then down to a lower level of it. Siphon will fail to work if, the level of the liquid in the two vessels are at the same height.

Spectrum of an oil frame is an example for continuous emission spectrum.

The instrument for measuring intensity of earthquakes is called Seismograph.

Geothermal energy is heat energy generated and stored in the Earth. Geothermal energy has been used for thousands of years in some countries for cooking and heating.