The answer is 1.
here is the details:

S1,S2,S3

Switch ON all 3 switches one by one. dont visit the room as bulb will be glowing for sure.
Then,  Switch OFF S3, check bulb on or off, If OFF, then Minimum visit=1;
else
Switch OFF S2 leaving S3 in OFF, check bulb on or off, If OFF, then  visit=2;
else
Then,  Switch OFF S1 leaving S3,S2 off, check bulb on or off, If OFF, then  visit=3;

\Hence ,
Minimum visit=1 and maximum vist=3

I guess it is the Science Teacher who has snatched the chain. So, Science teacher is not shouting at all. He might be busy running..!!!!

I agree to disagree on the above answer, as on his 22 th day Leap, he will reach the 30m wall and instead of falling back 3 m, he will move on.