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What happens to the intensity of light from a bulb if the distance from the bulb is doubled? As a laser beam travels across the length of room, its intensity essentially remain constant.
What geometrical characteristic of LASER beam is responsible for the constant intensity which is missing in the case of light from the bulb?
What geometrical characteristic of LASER beam is responsible for the constant intensity which is missing in the case of light from the bulb?
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Bulb spreads its light in all around spherically and symmetrically. So, if the distance is doubled, the area of spherical region $\left(4 \pi r^2\right)$ will become four times.
So, the intensity becomes one fourth the initial value in straight line for spherical source $\left(\mathrm{I} \propto 1 / 4 \pi \mathrm{r}^2\right)$ but in case of laser it does not spread in all directions, so its intensity remain almost same.
Geometrical characteristic of LASER beam which is responsible for the constant intensity are :
(i) Unidirection (ii) Monochromatic
(iii) Coherent light (iv) Highly collimated
These characteristic are missing in the case of light from the bulb.
So, the intensity becomes one fourth the initial value in straight line for spherical source $\left(\mathrm{I} \propto 1 / 4 \pi \mathrm{r}^2\right)$ but in case of laser it does not spread in all directions, so its intensity remain almost same.
Geometrical characteristic of LASER beam which is responsible for the constant intensity are :
(i) Unidirection (ii) Monochromatic
(iii) Coherent light (iv) Highly collimated
These characteristic are missing in the case of light from the bulb.
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