Two identical metal bars have the same dull surface. One bar is kept at a steady 300 °C and the other at a steady 600 °C. The diagram shows infra-red radiat...
Question 1 Report
Two identical metal bars have the same dull surface. One bar is kept at a steady 300 °C and the other at a steady 600 °C. The diagram shows infra-red radiation leaving each bar. 
Which bar gives out thermal radiation at the greater rate?
Answer Details
The rate at which an object emits thermal radiation increases with its temperature. The hotter an object is, the more infrared radiation it emits per second. Since the bar at 600 °C is at a much higher temperature than the bar at 300 °C, it radiates energy at a significantly greater rate.
In fact, the rate of radiation is proportional to the fourth power of the absolute temperature (the Stefan-Boltzmann law), so even a moderate increase in temperature produces a dramatic increase in radiation output. Both bars have identical surfaces and dimensions, so the only variable is temperature. The diagram illustrates this by showing more radiation waves leaving the hotter bar. Neither bar stops emitting radiation at any temperature above absolute zero.
Download The App On Google Playstore
Everything you need to excel in your exams
