Question

what is the cause of convection corrent

Answer 1

Convection currents are caused by temperature differences in a fluid (liquid or gas) that produce density differences, and gravity acting on those density differences.

How it works, simply:
- A heat source warms part of the fluid. The warmed fluid expands, becomes less dense, and so is buoyed upward.
- Cooler, denser fluid flows in to replace the rising warm fluid.
- That cooler fluid is heated in turn, rises, and the cycle repeats, creating a circulating flow — a convection current.

Key ingredients: a temperature gradient, a fluid that can move, and gravity (so buoyancy can act). Fluid properties (viscosity, thermal expansion coefficient) and the strength of heating determine how strong and organized the currents are. There is also "forced convection," where an external driver (fan, pump) moves the fluid rather than buoyancy.

Examples: boiling water, a lava lamp, atmospheric convection (thermals, thunderstorms), sea breezes, and mantle convection that drives plate tectonics.

If you want, I can show the basic buoyancy equation or explain the Rayleigh number that predicts when convection starts.