Monthly Archives: July 2011

Capacitor Puzzle Redeux

Posted on 25-July-2011 by mathscinotes

My first blog post discussed the following interview question I received many years ago. You are handed a 1 F capacitor charged to 10 V and two boxes containing uncharged capacitors: one box contains an uncharged 1 F capacitor and … Continue reading →

Posted in Electronics | 4 Comments

Thermistor Mathematics

Posted on 22-July-2011 by mathscinotes

A common electrical engineering task during the design of a circuit card is designing a way for the circuit to measure its own temperature. Knowing the temperature of a circuit board is important for compensating for component temperature variations and diagnosing heat problems. Normally, I use a thermistor as my temperature probe. A thermistor is a resistor whose resistance varies with temperature (Figure 1). The thermistors that I use have a negative temperature coefficient (NTC), which means their resistance reduces as their temperature increases. In many ways, thermistors are a great sensor: cheap, tough, small, and accurate. Continue reading →

Posted in Electronics | 35 Comments

Speed of a Meteor

Posted on 8-July-2011 by mathscinotes

I own a small cabin on a lake in Northern Minnesota. Years ago I showed my brother how to find satellites, planets, and meteors. I love to lay on the dock at night and watch the sky. Because Northern Minnesota is so sparsely populated, the sky is incredibly dark and the stars are so much brighter than in the metropolitan region where I spend most of my time. When people visit me at the cabin, I take them out on the dock and introduce them to the world of meteors, satellites, and planets. It is always a good time. Continue reading →

Posted in Astronomy | 28 Comments