Burning wood often pops and crackles • The reason why a burning wood pops and crackles is because of two things. First is due to the property of conduction. Wood is not a very good conductor of heat. Second reason is due to thermal expansion. An increase in temperature in any matter results to a change in the volumetric property of matter. Wood expands when heated or in this case burned. The burning part of the wood is expanding but since wood is not a good conductor of heat, the other parts of the wood that is not burning only experiences a very little amount of increase in temperature.
Thus, the expansion of the unburned parts of the wood is very minimal or negligible. The burning part of the wood continues to expand and exerts pressure on to the other unburned parts of the wood. When the wood could not contain the pressure, the burning/expanding part cracks which makes a popping sound. b. You cannot make a three-minute egg a two-minute egg in boiling water by turning up the heat • The concept behind this is heat transfer from the boiling water to the egg.
Even if we try to turn up the heat, the boiling water would still have a temperature of 100oC, since it is already the boiling point of water at room temperature and constant air pressure. The heat being transferred to the egg is proportional to the difference in temperature between the egg and the surrounding, which is the boiling water. Since the temperature of the water stays at 100oC, the difference between the egg and the water would not increase, thus would also not increase the amount of heat being transferred. 2. Concept behind plane mirrors
We can use ray tracing method to analyze and solve this problem. Since plane mirrors have a magnification equal to 1, the size of the image is equal to the size of the actual object. In figure 1, the red broken line is the perpendicular line at the point of reflection. The angle of the incident light ray is equal to the angle of the reflected light ray. Since the length of the incident ray and the reflected ray is equal, we can say that the image that can be seen is equal to twice the height of the mirror, which equates to 2m*2=4m.
So this means that the man can see 4/6 or 66. 67% of his image. In figure 2, we can see that even though the man moved an additional 5ft. away from the mirror, the amount of the image he can see is still 66. 67%. 3. Sound waves a. The equation v=? f holds true for sound waves. The velocity v of the sound is constant when propagating in air. So this means that sounds with different frequencies will travel at the same speed in air, but with different wavelengths ?. Thus both sounds will reach your ear at the same time.