today mr physics teacher did a demonstration on light dependent resistor(LDR). she shined a torchlight on the LDR and the buzzer buzzed. So i asked, how about using the OHP? she allowed me. so i used the mirror to aim at the LDR and the buzzer buzzed without the need to laboriously hold the torchlight.

Then i suggested putting the LDR at the focal point of the OHP. HuangLu stopped me, for fear it might melt the LDR. Then my physics teacher put her hand into the OHP and said "Not hot what."

So i took a piece of paper and held it still at the focus. The effect was brilliant. Within 3 seconds the piece of paper yielded to a 1 inch diameter hole and in 1 minute, the entire classroom smelled of smoke. Then, she said: "Okay i see your point."