# Tag Info

### Why does the energy (and thus frequency) of a photon entering glass stay constant if some is used up to accelerate electrons and slow down the light?

Your explanation of refraction is quite correct. The electric field of the light interacts with the electrons in the medium and we get an entangled system of light + electrons. This means the energy ...
• 355k
1 vote

### Why is a bigger camera sensor better at low light than a smaller one?

This is really an engineering issue, not a physics one. The problem is this: If you need a bigger lens to gather in all that light, it is, by necessity, going to make a bigger camera. As the lens is ...
1 vote

### Why is a bigger camera sensor better at low light than a smaller one?

Think of light as rain falling on your sensor. A bright light is a downpour. A dim light is a sprinkle. You want to know how much rain fell on a patch of ground. You can set up a funnel and a test ...
• 38.7k
Accepted

### Can the velocity of an image produced by a plane mirror be greater than that of light?

I checked you equation ($V_i = 2V_m - V_o$) and it appears to be correct. (See caveat below.) Can we say that if the mirror is moving with a speed 80% the speed of light and the object is moving with ...
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### If a star's luminosity doubles, does its received flux double?

Flux $F$ is related to luminosity $L$ and distance $d$ as $$F = \frac{L}{4\pi d^2} ,$$ assuming that the luminosity is radiated isotopically and there is no absorption in interstellar space. If $L$ ...
• 131k

### Is there a way to calculate the angle between the refracted and reflected rays given the refractive index?

Both reflection and refraction can be explained using Snells Law: Reflection $$n_1\sin\theta_i = n_2\sin\theta_r$$ where $\theta_r$ is the angle of reflection and $\theta_i$ is the angle of incidence. ...
• 2,002
Accepted

### Is there a way to determine whether what I see is a source of light, a real image, or a virtual image?

In principle, there is no difference between photons traveling from an object through the air and photons traveling through an optical setup. Photons are photons. That being said, it is very ...
• 49k

### Is there a way to calculate the angle between the refracted and reflected rays given the refractive index?

According to the law of reflection for light rays, the incident ray angle 𝛂 is equal to the reflected ray angle (with respect to the normal to the interface). Snell's law relates the ratio of the ...
• 16.1k
Accepted

### If a silver screen works for a movie projector then why not a mirror?

A solid mirror would reflect the light beam from the projector straight back towards the projector. The audience nearest the projector might see the brilliant beam as a blindingly bright point source, ...
• 92.8k
1 vote

### Light from an eclipse

During the darkest parts of the eclipse, your pupils may dilate to adjust to the darkness. A reasonable hand-waving estimate for the difference in area between a fully-constricted pupil versus a fully-...
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### Light from an eclipse

People generally avoid staring at the sun; it's bright and painful and will damage your eyes. During an eclipse people want to watch the eclipse happening and without approved darkened glasses they ...
• 829
1 vote

### Could another star render color better than the Sun? If so, would a human be able to tell?

The spectrum of the light source does matter. You can see this with lights of different color temperature. Lower color temperatures emphasize the warmer, redder colors. Higher color temperatures ...
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### Could another star render color better than the Sun? If so, would a human be able to tell?

The human visual perception system performs extensive processing. Among the features achieved by that processing is color constancy Color constancy is that the visual system is still able to suss out ...
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### What is a laser spectrum?

What is a laser spectrum? The spectrum of the laser is a function telling you how much power (or power spectral density) the laser outputs at each frequency or wavelength.   How many wavelengths can ...
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### What is a laser spectrum?

You are probably talking about the helium-neon laser: The best-known and most widely used He-Ne laser operates at a wavelength of $632.8$ nm (in air), in the red part of the visible spectrum. This ...
• 39.6k
1 vote

### Will the Intensity of parallel light rays decrease over distance?

If the area the light is spread over does not increase and the light is not absorbed, then intensity will not decrease. If you had a perfectly parallel beam of light, one would not see the intensity ...
• 49k

### Will the Intensity of parallel light rays decrease over distance?

**Certainly! The intensity of parallel light rays does indeed decrease with distance. This phenomenon follows the inverse square law. Let me explain: Imagine a point light source (like a bulb or the ...
Accepted

### What is the emission spectrum of an igniting match?

The intense orange line is probably from a mix of phosphorus and sodium. You can calibrate your spectrophotometer by looking at a compact fluorescent bulb with it; you'll see a prominent ...
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### Is reflected photon the same?

Speaking of photons means we treat light as quantum particles. In the quantum world there is a principle of indistinguishable particles, i.e. particles with the same quantum numbers cannot be ...
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### Is reflected photon the same?

at this scale how do you define original? because in the end it's just energy. a wave reflecting back or a photon reflecting back obeying their characteristic nature.

### Why does a photomultiplier tube (PMT) traditionally present better signal-to-noise ratio (SNR) than an avalanche photodiode (APD)?

I don't know much about the difference between PMT and APD, but if PMT has a higher gain than APD, than perhaps a larger portion of photons reaching the PMT can be detected than APD. The number of ...
1 vote
Accepted

### Why do we see objects with a given color?

When light hits an object, it may be reflected, transmitted, or absorbed. Each photon undergoes one of these. There is more than one way to change the fraction of incident light that gets each outcome....
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### Why no image is formed when an incident and reflected ray intersect?

I do not agree with what SaaN has said. I do agree with what John has to say (though the answer does not address the main issue of the question). This simulation might help you to understand how many ...

### Why no image is formed when an incident and reflected ray intersect?

The diagram is simplified. You get an image when a whole bundle of rays converge, not just two. Every ray from point A that reflects from the mirror (ideally) reaches point A', not just the two rays ...
• 21k