INSTRUCTOR PLT MAKES A PRECAUTIONARY LNDG AFTER DETECTING SMOKE IN THE COCKPIT. SOURCE OF THE SMOKE WAS THE STUDENT PLT SMOKING A CIGARETTE.

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I WAS FLYING WITH MY STUDENT FOR HIS PVT PLT PRACTICAL EXAM WHEN THE SIT OCCURRED. WE ARRIVED AT THE ARPT EARLY; SO I DECIDED TO GO OVER POSSIBLE PITFALLS THAT HIS DESIGNATED EXAMINER MAY INTRODUCE DURING THE FLYING PORTION OF THE PRACTICAL EXAM. ONE OF THESE PITFALLS WOULD BE AN ACCIDENTAL APCH INTO A NEARBY CLOSED ARPT. 1 MI W OF ZZZ IS THE OLD ZZZ ARPT; WHICH IS CLOSED. THE 2 ARPTS ARE CLOSE TOGETHER AND BOTH HAVE THE SAME RWY HDGS OF 18 AND 36. I SHOWED MY STUDENT THE CLOSED ARPT AND THEN TURNED N TO SHOW HIM ANOTHER ARPT HE WOULD LIKELY BE ASKED TO DIVERT TO DURING THE NAV PART OF THE PRACTICAL EXAM. I TOLD MY NERVOUS STUDENT TO RELAX WHILE I FLEW US THERE. I TOOK THE FLT CTLS AND HE SLID HIS SEAT BACK TO RELAX. I LOOKED OUT THE R WINDOW FOR POSSIBLE TFC AT THE NEW ZZZ. I WAS ABOUT TO ANNOUNCE MY NBOUND DEP FROM THE AREA WHEN SUDDENLY I SMELLED SMOKE. MY REACTION TO THE SMELL OF SMOKE IN THE COCKPIT WAS TO LAND IMMEDIATELY. THE QUICKEST WAY TO LAND WOULD BE TO ENTER A R BASE FOR RWY 18 AT ZZZ. I IMMEDIATELY ANNOUNCED MY INTENTIONS. I THEN ASKED MY STUDENT IF HE SMELLED THE SMOKE. I GOT NO RESPONSE FROM MY STUDENT. A SECOND LATER; I HEARD SOMEONE ON THE FREQ SAY; 'BE ADVISED ZZZ L TFC.' I HAD BEEN MONITORING THE ZZZ FREQ AND WAS KEEPING TRACK OF THE ARPT'S TFC IN MY HEAD. I THOUGHT ALL OF THE TFC WAS ON THE GND! WHEN I HEARD 'BE ADVISED L TFC;' I THOUGHT THAT I MUST HAVE HEARD PART OF A XMISSION AND MAYBE SOMEONE WAS IN THE PATTERN MAKING L TFC. I ANNOUNCED THAT I WAS TURNING R BASE. NO RESPONSE! I VIGILANTLY BEGAN LOOKING FOR THE POTENTIAL TFC. I CONTINUED TO SCAN FOR THE TFC. UNABLE TO SEE ANYTHING; I ASKED MY STUDENT IF HE SAW ANY TFC. AGAIN; I GOT NO RESPONSE FROM MY STUDENT. ONCE I HAD THE RWY MADE; I LOOKED INSIDE THE COCKPIT TO GLANCE AT THE ENG GAUGES. SHOULD I PULL THE MIXTURE? DOES THE SMOKE SMELL LIKE AN ELECTRICAL FIRE OR GAS? MAYBE I SHOULD TURN OFF THE MASTER SWITCH! I GLANCED AT MY STUDENT TO SEE WHY HE WASN'T REACTING TO THE SIT. AFTER ALL; IT WAS HIS AIRPLANE THAT WAS POTENTIALLY ON FIRE. THAT WAS WHEN I REALIZED WHERE THE SMOKE WAS COMING FROM. THERE; TO MY L; SAT MY STUDENT -- HEADSET AROUND HIS NECK -- SMOKING A CIGARETTE! THIS TOOK ME BY SURPRISE FOR A COUPLE OF REASONS: 1) I DIDN'T KNOW MY STUDENT SMOKED; 2) I'VE NEVER SEEN ANYONE SMOKE IN AN AIRPLANE BEFORE. I FELT AMAZINGLY DUMB AT THAT PARTICULAR MOMENT. I LOOKED AT THE APCH END OF THE RWY AND NOTICED 3 CONFUSED CESSNA PLTS HOLDING SHORT OF RWY 18; WHERE I THOUGHT THEY SHOULD BE; PROBABLY WONDERING WHY I WAS MAKING R TFC. I BELIEVE THAT THIS SIT OCCURRED BECAUSE OF LACK OF COM BTWN MY STUDENT AND ME. I BELIEVE THAT THIS SIT COULD HAVE BEEN AVOIDED IF I HAD ASSESSED THE SIT A LITTLE LONGER INSTEAD OF JUMPING ON MY FIRST REACTION. I ALSO BELIEVE THAT IN THE EVENT OF AN EMER; CRM SHOULD BE HIGHER ON MY LIST OF PRIORITIES.