A flat piece of glass is held stationary and horizontal...

A flat piece of glass is held stationary and horizontal above the highly polished, flat top end of a 10.0 -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 $500 \mathrm{nm}$. As the temperature is slowly increased by $25.0^{\circ} \mathrm{C}$, the film changes from bright to dark and back to bright 200 times. What is the coefficient of linear expansion of the metal?

Key Concepts

Thin Film Interference

Thin film interference occurs when light waves reflect off the two surfaces of a thin layer, causing the reflected waves to interfere constructively or destructively based on the difference in path lengths. This phenomenon depends on the film's thickness, the wavelength of light, and the phase changes upon reflection. It is fundamental in analyzing how variations in optical path length lead to shifts in observed interference patterns.

Thermal Expansion

Thermal expansion is the tendency of a material to change its dimensions in response to a change in temperature. The coefficient of linear expansion quantifies this change per unit length per degree of temperature change. This concept is crucial in determining how temperature variations affect the physical dimensions of objects, which in turn can alter distances that influence other physical phenomena.

Fringe Counting in Interferometry

In interferometry, fringe counting is a method used to measure small changes in distance by analyzing the number of interference fringes that appear or disappear as a system changes. Each fringe typically corresponds to a specific fraction of the wavelength shift, allowing precise calculation of dimensional changes. This method is essential for connecting observable interference patterns with minute physical changes, such as those resulting from thermal expansion.

Transcript

Please give Ace some feedback