I/p impedance of an opamp is very high and hence very little current flows thru it's inputs and hence very little voltage drop occurs at i/p.Hence if one of it's i/p is grounded ,since voltage difference b/w two i/ps will be very less we can assume other one of the i/p also to be at ground and hence giving rise o term 'virtual gound'.
virtual ground ... there r two inputs to an Opamp now
whatever voltage is present at 1 input ...same is assumed to present at 2nd input too!
this concept is very vital ..
In general, the concept of "virtual ground" has wider meaning than the above ..
Sometimes it is called a "rail splitter": it splits a single supply in two, so you have two "voltage rails" plus "new" ground - the virtual ground ..
Here you will find more: https://tangentsoft.net/elec/vgrounds.html
due to -ve feedback the -ve terminal approaches the +ve terminal since the gain of opamp is in 1000's .we say the -ve terminal of opamp is at virtual gnd (virtual since not really grounded)if +ve terminal is at gnd.
The op-amp has two input terminals. When the op-amp is used with some negative feedback around it, the two input terminals are at same potential [ideally], although they are physically not connected together. This is referred to as VIRTUAL SHORT [and NOT virtual ground]. In case one of the terminal is kept at GROUND Potential, then the other one is also at GROUND Potential. This can be referred to as VIRTUAL GROUND.
Both the inverting and non inverting inputs of an opamp are bootstrapped to each other. If one is set to a certian voltage the other input will follow......