Convection (for Class 7) is the transfer of heat in liquids and gases by the actual movement of the heated particles of the medium.

Simple definition (Class 7 level)

  • When a liquid or gas is heated, the warmer part becomes lighter (less dense) and rises up.
  • The cooler part is heavier (more dense) and moves down to take its place.
  • This continuous rising of hot fluid and sinking of cold fluid sets up a “convection current” and carries heat from one place to another.

So, convection is heat transfer in water or air because the hot part moves and carries heat with it.

Class 7 style examples

  • Heating water in a pan: Water near the flame heats up, becomes lighter, rises; cooler water comes down, and after some time the whole water becomes hot.
  • Sea breeze and land breeze: In the day, air over land heats up, rises, and cooler air from the sea moves in to take its place (sea breeze). At night, the opposite happens (land breeze). These are due to convection of air.
  • Warm air at the ceiling: In a room with a heater, air near the heater becomes warm and rises upwards, so the upper part of the room feels warmer.

Key points to remember for exams

  • Convection happens only in liquids and gases , not in solids.
  • It involves actual movement of the medium’s particles.
  • It creates convection currents (a loop of rising warm fluid and sinking cool fluid).

If you want, I can also give you a 2–3 line answer exactly in the format “What is convection?” for writing in your notebook.