Why Does The System Pressure Decrease In An Isothermal Expansion?

[Mohankpbk]

In a piston cylinder arrangement, the piston can be extended only if the pressure of the gas inside is higher than the atmospheric pressure.In case of isothermal expansion of ideal gas, initially the piston is at rest(gas pressure is equal to the atmospheric pressure) and as energy is given to the system (heat is given to the system) the piston moves.Doesnt this mean the pressure of the gas increases above the outside pressure?(But I have learnt that pressure never increases in an isothermal expansion, it decreases with increase in volume(hyperbolic relation))

[Maine farmer]

Pressure can only increase if you provide resistance to the piston.  When there is resistance on the piston, pressure will increase until that resistance is overcome, the piston will move, and pressure will equalize.