Class 12 cbse project youngs double slit experiment
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. COHERENT SOURCES
The sources of light, which emit continuous light waves of the same wavelength, same frequency and in the same phase difference are called coherent sources.
Conditions to obtain coherent light :
1. Two sources should be single source or by same device.
2. Two sources should give monochromatic light.
3. The path difference b/w light waves from 2 sources should be small.2. INTERFERENCE OF LIGHT
It is the phenomenon of redistribution of light energy in a medium on account of superposition of light wave from 2 coherent sources. There are 2 types:
1. Constructive Interference.
2. Destructive InterferenceEXPERIMENT
Young’s Double Slit Experiment
Set up the apparatus as in the Figure 1.
The appearance of bright and dark fringes on screen can be explained on the basis of interference of light. According to Huygens principle, the monochromatic source of light illuminating the slit S sends out spherical wavefronts. Let the solid arcs represent the crests ant the dotted arcs represents the troughs. These wavefronts reach the slits A and B simultaneously which in turn, become sources of secondary wavelets. Thus the 2 waves on superposition produce interference.
The dots (.) represent the positions of constructive interference, where crests of one wave falls on crests of the other and trough falls on trough. The resultant Amplitude and hence intensity of light is maximum at these positions. The lines joining the dots lead to points C, E, G on the screen.
Similarly, the crosses (x) represent the positions of destructive interference, where crest of one wave falls on trough of the other and vice-versa. The resultant amplitude and hence intensity of light is minimum at these positions. The lines joining the crosses lead to points D, F on the screen.
Thus we have Bright Fringes at C, E, and G and Dark Fringes at D and F.
These bright and dark fringes are placed alternatively and they are equally spaced. These are called INTEFERENCE FRINGES.
INTERFERENCE PATTERNS
Conditions for constructive and Destructive Interference,Constructive Interference (For Sustained Inerference)
1. The 2 sources of light must be coherent i.e. they continuous light waves of same wavelength or frequency, which have either same phase of constant path difference.
2. The 2 sources should be strong with least background.
3. The amplitudes of waves from 2 sources should preferably be equal.
4. The 2 sources should preferably be monochromatic.
5. The coherent sources must be very close to each other.
6. The 2 sources should be point and narrow sources.
The sources of light, which emit continuous light waves of the same wavelength, same frequency and in the same phase difference are called coherent sources.
Conditions to obtain coherent light :
1. Two sources should be single source or by same device.
2. Two sources should give monochromatic light.
3. The path difference b/w light waves from 2 sources should be small.2. INTERFERENCE OF LIGHT
It is the phenomenon of redistribution of light energy in a medium on account of superposition of light wave from 2 coherent sources. There are 2 types:
1. Constructive Interference.
2. Destructive InterferenceEXPERIMENT
Young’s Double Slit Experiment
Set up the apparatus as in the Figure 1.
The appearance of bright and dark fringes on screen can be explained on the basis of interference of light. According to Huygens principle, the monochromatic source of light illuminating the slit S sends out spherical wavefronts. Let the solid arcs represent the crests ant the dotted arcs represents the troughs. These wavefronts reach the slits A and B simultaneously which in turn, become sources of secondary wavelets. Thus the 2 waves on superposition produce interference.
The dots (.) represent the positions of constructive interference, where crests of one wave falls on crests of the other and trough falls on trough. The resultant Amplitude and hence intensity of light is maximum at these positions. The lines joining the dots lead to points C, E, G on the screen.
Similarly, the crosses (x) represent the positions of destructive interference, where crest of one wave falls on trough of the other and vice-versa. The resultant amplitude and hence intensity of light is minimum at these positions. The lines joining the crosses lead to points D, F on the screen.
Thus we have Bright Fringes at C, E, and G and Dark Fringes at D and F.
These bright and dark fringes are placed alternatively and they are equally spaced. These are called INTEFERENCE FRINGES.
INTERFERENCE PATTERNS
Conditions for constructive and Destructive Interference,Constructive Interference (For Sustained Inerference)
1. The 2 sources of light must be coherent i.e. they continuous light waves of same wavelength or frequency, which have either same phase of constant path difference.
2. The 2 sources should be strong with least background.
3. The amplitudes of waves from 2 sources should preferably be equal.
4. The 2 sources should preferably be monochromatic.
5. The coherent sources must be very close to each other.
6. The 2 sources should be point and narrow sources.
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Young in 1801 demonstrated interference phenomenon through double slit experiment
In his experiment ,he divided a single wave front into two and these two slit wave fronts acts as if they emerged from two sources having fixed relationship
when these two waves were allowed to interfere ,they produce a sustained interference pattern
In his original experiment he illuminates a pin hole S using a light source and light diverging from pinhole which contains two sets of pinholes S1 and S2 equidistant from S and very close to one another as shown below in the figure
Two two sets of spherical waves coming out of the pin holes S1 and S2 were coherent and interfered with each other to form a symmetrical pattern of varying intensity on screen XY
This interference pattern disappear when any one of the pinholes S1 or S2 is closed
Young used the superposition principle to explain the interference pattern and by measuring the distance between the fringes he managed to calculate the wavelength of light.
In his experiment ,he divided a single wave front into two and these two slit wave fronts acts as if they emerged from two sources having fixed relationship
when these two waves were allowed to interfere ,they produce a sustained interference pattern
In his original experiment he illuminates a pin hole S using a light source and light diverging from pinhole which contains two sets of pinholes S1 and S2 equidistant from S and very close to one another as shown below in the figure
Two two sets of spherical waves coming out of the pin holes S1 and S2 were coherent and interfered with each other to form a symmetrical pattern of varying intensity on screen XY
This interference pattern disappear when any one of the pinholes S1 or S2 is closed
Young used the superposition principle to explain the interference pattern and by measuring the distance between the fringes he managed to calculate the wavelength of light.
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