Optics
1. What does physical optics study?
Solution:
Physical optics deals with the wave properties of light. It studies
- the nature of light
- the origin of light
- the propagation of light
- reflection and refraction of light
- interference of light by reflection and diffraction
- dispersion of light
- polarization of light
Light is electromagnetic radiation with wavelengths in vacuum (air) from 380nm to 760nm (7.8·1014Hz to 3.8·1014Hz). The phase velocity of light in vacuum (air) is c = 3·108m·s-1. In other substances, v < c.
- Source of light: A body that emits electromagnetic radiation with wavelengths λ = 380nm – 760nm.
- Light detector: A device for receiving and recording light
- Optical medium: Transparent, opaque, translucent, homogeneous.
- Propagation of light: In a homogeneous medium, light propagates in a straight line.
- Fermat’s principle: If a light ray passes between two points, it always chooses the path that takes the shortest time.
- Principle of independence of rays: If two light rays intersect, they do not affect each other and proceed independently through the medium.
2.In how much time does light reach Earth from the Moon and from the Sun? The distance Moon – Earth is 384,450 km and the distance Sun – Earth is 150,000,000 km.
Solution:
Analysis:
Light travels from the Moon to the Earth in 1.28 seconds, from the Sun to the Earth in 8.33 minutes.
3.Light travels in vacuum a distance equal to the length of the equator in 0.1335 seconds. Determine the radius of the Earth.
Solution:
Analysis:
t = 0.1335s, c = 3·108m·s-1, R = ?
The radius of the Earth is R = 6378 km.
4.Sirius A, the brightest star in our entire sky, is 8.69 light years away from us. How many meters is that?
Please log in to view the solution.5.How tall is a tree that casts a shadow 36m long, if the height of the Sun is α = 240? How long a shadow does a building 44.52m high cast at the same time?
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6. Astronomers have found that every minute, 2·10-18kg of light falls on Earth per 1m2. How many kilograms of light fall on our planet in one year? R = 6378km = 6.378·106m. 1 year = 31557600s.
Please log in to view the solution.7.A human perceives electromagnetic waves in air from 389 nm to 789 nm as light. Determine the frequencies corresponding to the given wavelengths. Find out whether a human perceives electromagnetic radiation with frequency f = 9.5·1014 Hz as light.
Please log in to view the solution.8.A point light source is at a distance h = 1.2 m from a screen. How long will the shadow on the screen be if, at a distance
h/ = 0.4 m from the screen and parallel to it, there is a ruler of length d = 0.3 m?
9.How long does it take for light to pass through a layer of glass ( n = 1.5 ) with a thickness of d = 2 cm?
Please log in to view the solution.10.How tall is a pillar if the observer’s eye can distinguish it from a distance of 10 km? The resolving power of the eye is about 1/.
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