Rahat34 said:
photoelectric effect is explained by taking photon of energy 'hv'.Even electromagnetic waves carry energy.Why can't they interact with electron and transfer energy ?Even a wave has characteristics frequency and wavelength charateristics and all. I think I'm a bit confused.Can someone help me?
A wave also has a characteristic amplitude. The amplitude of a wave is treated a little differently in classical physics than in quantum physics.
In classical physics, the amplitude of a wave has to change in infinitesimal steps at any instant of time. Here, infinitesimal means too small to possibly detect. Also in classical physics, the rate of absorbing energy is determined precisely by the characteristics of the wave. There is no rate of transfer that is "random". Even if the atoms are exchanging energy, they can't transfer energy to one atom because all atoms are alike. The symmetry of energy transfer prevents a net concentration of energy.
Classical physics makes a prediction that is not seen in experiment. When the electromagnetic waves enters the surface of the material, all the atoms in the materials are being exposed to the same characteristics. So each atom has to absorb energy at the exact same rate. Of course, this means that the rate of absorbing energy of each atom is extremely small. It takes a long time for the electron in the atom to accumulate enough energy to leave. So according to classical physics, each electron should be waiting "patiently" until it has enough energy to jump out of its atom. Then, the electrons should all jump out of the atom at the same time. If very low intensity light is used, the waiting time can be long enough to detect and measure. This waiting time has not been observed in experiments. Even in very dim light, some electrons jump out right way.
In quantum physics, the amplitude has to change in finite steps which are consistent with wave-particle duality. Each "particle" associated with the wave correlates with a step in the amplitude of the wave. Furthermore, the energy transfer can have a random component in time. All atoms are alike until the random component of energy transfer makes them different.
The experimental results are predicted by quantum physics. When light of very low intensity enters a material, all atoms are exposed to a wave with the same characteristics. The amplitude, frequency and wavelength is the same for each atom. So the average rate of energy transfer for all atoms is precisely the same as in the quantum case. However, the rate of transfer for each individual atoms is not the same as the average rate because there is a random component to energy transfer.
The amplitude can change suddenly. In fact, the amplitude has to change suddenly. Therefore, at least some of the atoms collect enough energy to make the jump immediately after the light is turned on. The amplitude of the light wave then decreases in a finite step corresponding the the absorption of a "photon". There is a delay in jumping time which varies with each atom. For some atoms, the delay time are longer than the average time. However, the average waiting time is the same as determined by the classical theory. The experimental result that violates classical theory is that there is a finite spread in the waiting times.
Historically, the idea of quantized amplitude came before the idea of wave-particle duality. Quantization of amplitude in a atom as a harmonic oscillator was the idea of Planck. Einstein came up with idea that the amplitude of light can come in discrete steps. However, Einstein posed the idea in terms of light being composed of particles. The two concepts are really one concept, since the physical predictions made by the theory are similar.
Quantum physics is notoriously anti-intuitive compared to classical theory. You don't have to like it. However, it does provide predictions that are closer to experimental fact than classical physics.
