A) `upsilon lt upsilon_0 to ` no photo current B) `lambda lt lambda_0 to ` photo electron emitted, no photo current C) `upsilon gt upsilon_0 to ` photo electron emitted , no photocurrent D) `lambda gt lambda_0 to ` K.E. of phto electron `=h(upsilon- upsilon_0)`, velocity of photo electron `=sqrt((2ch)/(m) ((lambda_0 -lambda)/(lambda lambda_0)))`
