2.7 Describe and identify experimental evidence for why electromagnetic radiation is a particle.

Claim

Electromagnetic radiation behaves as a particle, as shown by experiments like the photoelectric effect and Compton scattering.

Evidence

1. Photoelectric Effect:

• When light hits a metal, it ejects electrons, but only if the light has a certain frequency.

• This suggests light is made of photons, which carry energy based on their frequency.

2. Compton Scattering:

• X-rays scatter off electrons, and the change in energy and wavelength depends on the scattering angle.

• This shows that light has momentum and behaves like a particle.

3. Blackbody Radiation:

• Objects emit light in specific wavelengths when heated.

• Planck's idea of energy quanta (discrete packets) explains this, supporting light as particles.

Reasoning

These experiments show that electromagnetic radiation exhibits particle-like properties such as carrying energy and momentum, which are not explained by wave theory alone. Therefore, light behaves both like a wave and a particle.

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