Light consists of tiny 'corpuscles' called photons that possess momentum. This can be demonstrated with a radiometer, shown in the sketch. Metal vanes are painted black on one side and white on the other and are free to rotate about the point of a needle mounted in a vacuum. When photons are incident on the black surface, they are absorbed; when photons are incident on the white surface they are reflected. Upon which surface is the impulse of light greater, and which way will the vanes rotate? Explain. 2.9 H. ครอบบนปลายเข็มแหลม

Light consists of tiny 'corpuscles' called photons that possess momentum. This can be demonstrated with a radiometer, shown in the sketch. Metal vanes are painted black on one side and white on the other and are free to rotate about the point of a needle mounted in a vacuum. When photons are incident on the black surface, they are absorbed; when photons are incident on the white surface they are reflected. Upon which surface is the impulse of light greater, and which way will the vanes rotate? Explain. 2.9 H. ครอบบนปลายเข็มแหลม