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Spherical mirrors do not focus parallel light rays to a single focal point. The focus actually lies on a surface called a caustic. Wolfram have a nice demonstration of this here. Light rays close to the centre of the mirror, i.e. the region where the mirror is only slightly angled away from the vertical, do come to a single focal point to a good ...

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Try to think the rope made up of small solid balls connected with springs. When you make the bump as shown in your picture the springs are expanded. Now you let go of it. The rising ball applies force upward to the ball on its right. The already expanded springs soon tend to decompress again. In doing so the the falling ball applies a downward force to ball ...

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The energy is reflected due to the discontinuity of the string mechanical impedance. Therefore it "can't be used as a part of the pulse" because it never gets to the denser rope. It's actually a special case of very general principle: whenever there is a discontinuity in propagation medium, energy reflection occurs. That's the same in optics, when you are ...

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This Q boils down to How bright is Earthshine? According to the usual source Oceans reflect the least amount of light, roughly 10%. Land reflects anywhere from 10–25% of the Sun's light, and clouds reflect around 50%. So the amount of sunlight reflected (i.e. albedo) depends on what part of the earth is facing your observer and how cloudy it is. ...

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This depends on the reflectivity of the objects and the size in the sky. The visual albedo of the moon when near (but not at) full, is about $0.12$. Earth's is around $0.39$. Being in low-earth orbit, the actual amount will vary based on the terrain and atmosphere. If it's overcast below, the value could be much higher. You can assume that a given area ...

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By denser, I assume you mean with a larger refractive index. The answer is established from the Fresnel equations giving the ratio of the electric field amplitudes. The reflection amplitudes for (for example) light travelling from glass to air can be either positive, negative or complex depending on the angle of incidence and the polarisation state of the ...

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