When you say that something was on TV, it means that it appeared on television.
Examples, I saw Bush and Blair on TV last night * When are you coming on TV”? *
‘Something is on the TV’ means something is there on top of the television set.
Examples, Your cat is on the TV * Your glasses are on the TV.”
S. Upendran , The Hindu- ‘Know Your English’ Series, January 7, 2003
