Hot Spots and Cold Spots

Hot spots and cold spots

When incoming waves and bounced-back waves overlap, some places always shake hard and others hardly shake at all. On the floor pattern, the bright places are strong “hot spots” and the dark places are weak “cold spots”. The still points are half a wave apart, about 6.1 cm. That is why food left still heats up only in patches.

Why?Hold a jump rope at both ends and shake it. Some parts swing widely and others barely move. The waves in the box do the same. Where the incoming and returning waves add up, they shake hard; where they cancel out, they hardly shake.

Learn moreA wave that sways in place like this is called a standing wave. Take out the turntable and warm a wide bar of chocolate for a moment: melted spots appear. In this calculation they are about 5.7 cm apart. Multiply by 2 and then by the number of wiggles per second, and you get the speed of light (about 278,000 km per second here; the real value is about 300,000). Careful, the chocolate gets hot.

Between the still points

6.1 cm

textbook formulas · example oven cavity 31.5 × 21 × 32.5 cm