14.1.1 Interference Conditions for Light Sources Suppose we are considering two light waves.In order to form an interference pattern,the incident light must satisfy two conditions: (i)The light sources must be coherent.This means that the waves from the sources must maintain a constant phase relation.For example,if two waves are phase shifted by o=, this phase shift must not change with time. (ii)The light must be monochromatic.This means that the light consists of just one wavelengthλ=2π/k. Light emitted from an incandescent light bulb is incoherent because the light consists of waves of different wavelengths and they do not maintain a constant phase relationship. Thus,no interference pattern is observed. Figure 14.1.3 Incoherent light source 14.2 Young's Double-Slit Experiment In 1801 Thomas Young carried out an experiment in which the wave nature of light was demonstrated.The schematic diagram of the double-slit experiment is shown in Figure 14.2.1. naximum minimum maximum maximum Figure 14.2.1 Young's double-slit experiment. 14-414-4 14.1.1 Interference Conditions for Light Sources Suppose we are considering two light waves. In order to form an interference pattern, the incident light must satisfy two conditions: (i) The light sources must be coherent. This means that the waves from the sources must maintain a constant phase relation. For example, if two waves are phase shifted by φ = π , this phase shift must not change with time. (ii) The light must be monochromatic. This means that the light consists of just one wavelength λ = 2π / k . Light emitted from an incandescent light bulb is incoherent because the light consists of waves of different wavelengths and they do not maintain a constant phase relationship. Thus, no interference pattern is observed. Figure 14.1.3 Incoherent light source 14.2 Young’s Double-Slit Experiment In 1801 Thomas Young carried out an experiment in which the wave nature of light was demonstrated. The schematic diagram of the double-slit experiment is shown in Figure 14.2.1. Figure 14.2.1 Young’s double-slit experiment