VISUAL PHYSICS ONLINE

7.1 THE NATURE OF LIGHT

ELECTROMAGNEITC WAVES

P71 005

(A)

Explain how an understanding of blackbody radiation changed the direction of

scientific thinking in the early twentieth century.

(B)

Beginning in the late 19^th century, observations and experiments on blackbody radiation and the Photoelectric Effect led physicists to revise their existing model of light.

(B1) What was the existing model for light?

(B2) What was the evidence for this model?

(B3) What model was introduced to explain blackbody radiation and the Photoelectric Effect?

(B4) Use the above as an example to explain how scientists test, validate and revise models.

View solution below only after you have completed the answering the question.

Solution

(A)

In classical physics, the energy of a system could have a continuous range of values, but Planck introduced for the first time the concept of discrete changes in energy of a system in his explanation of blackbody radiation. This was a radical idea at the time and one of the first steps in developing a new way to describe the world in terms of the ideas in modern physics.

(B1) Light was thought to be a wave phenomenon.

(B2) Light could produce as interference pattern a wave behaviour.

(B3) Light a stream of particles – photons.

(B4) Both the observations made on the photoelectric effect and blackbody radiation could not be explained in terms of classical physics – radial new ideas had to be introduced – e.g. energy quantization and light as both a particle and a wave