A flat piece of glass is held stationary and horizontal above the highly polished, flat top end of a 12.0-cm-long vertical metal rod that has its lower end rigidly fixed. The thin film of air between the rod and glass is observed to be bright by reflected light when it is illuminated by light of wavelength 490 nm. As the temperature is slowly increased by 21.5°C, the film changes from bright to dark and back to bright 200 times. What is the coefficient of linear expansion of the metal? °C-1

A flat piece of glass is held stationary and horizontal above the highly polished, flat top end of a 12.0-cm-long vertical metal rod that has its lower end rigidly fixed. The thin film of air between the rod and glass is observed to be bright by reflected light when it is illuminated by light of wavelength 490 nm. As the temperature is slowly increased by 21.5°C, the film changes from bright to dark and back to bright 200 times. What is the coefficient of linear expansion of the metal? °C-1