# Effect of light and sound to opaque object

• songoku
In summary, the opaque object has little effect on a beam of sound emitted by a small source of frequency 500 Hz because sound is a pressure wave, sound travels much more slowly than light, the power per unit area in a beam of sound is much lower than that in a beam of light, and the opaque object has a huge wavelength in the case of sound wave as compared to light waves.

## Homework Statement

An opaque object 10 cm wide casts a shadow when placed in a beam of light but has little effect on a beam of sound emitted by a small source of frequency 500 Hz. This is because
a. sound is a pressure wave whereas light is an electromagnetic waves
b. sound travels much more slowly than light
c. sound waves are longitudinal whereas light waves are transverse
d. sound waves have a much longer wavelength than light waves
e. the power per unit area in a beam of sound is much lower than that in a beam of light

Don't know

## The Attempt at a Solution

I don't know the relation between the choices and the question. I know that sound is longitudinal and light is transverse, I know the speed of sound and light. But I don't know how to use the info to answer the question.

Thanks

Think of the difference of wavelengths and Huygens–Fresnel principle and diffraction of waves.

ehild

with a huge wavelength in the case of sound wave as compared to light waves,the pressure waves can really move over the edges of the object.

ehild said:
Think of the difference of wavelengths and Huygens–Fresnel principle and diffraction of waves.

ehild

"The Huygens–Fresnel principle is a method of analysis applied to problems of wave propagation (both in the far field limit and in near field diffraction). It recognizes that each point of an advancing wave front is in fact the center of a fresh disturbance and the source of a new train of waves"

But I still don't know how to relate it with the question. Huygens-Fresnel principle says that there will be a new center of disturbance. So when the sound hits the opaque object, there will be a new center of disturbance at the object's surface. Why don't the sound being reflected?

abhishek ghos said:
with a huge wavelength in the case of sound wave as compared to light waves,the pressure waves can really move over the edges of the object.

OK, based on your hint, I think the answer is (d). But why with a huge wavelength in the case of sound wave as compared to light waves,the pressure waves can really move over the edges of the object?

Thanks

for your question! Based on the information given, we can infer that the main reason for the difference in effect of light and sound on the opaque object is due to the difference in their properties. Sound is a pressure wave, meaning it travels through molecules of a medium, while light is an electromagnetic wave that can travel through a vacuum. This difference in medium and mode of propagation can result in different interactions with the opaque object. Additionally, sound waves travel much slower than light waves, which can also affect their interaction with the object. Furthermore, sound waves have a longer wavelength compared to light waves, which can also contribute to their differing effects on the object. Lastly, the power per unit area in a beam of sound is much lower than that in a beam of light, which can also play a role in the observed differences. Overall, it is the combination of these factors that results in the opaque object having a greater effect on light compared to sound.

## What is the effect of light on opaque objects?

The effect of light on opaque objects is that it causes the object to reflect or absorb the light. Opaque objects do not allow light to pass through them, so the light is either reflected off the surface or absorbed into the material.

## What is the effect of sound on opaque objects?

The effect of sound on opaque objects is that it causes vibrations in the object. Sound waves are created when an object vibrates, and these waves can cause other objects to vibrate as well. Opaque objects are not transparent to sound, so they will absorb and reflect the sound waves.

## How does the color of an opaque object affect its reaction to light and sound?

The color of an opaque object can affect its reaction to light and sound. Darker colors tend to absorb more light and sound, while lighter colors tend to reflect more. This is because darker colors have a higher concentration of pigments, which absorb more light and sound waves.

## Does the texture of an opaque object affect its reaction to light and sound?

Yes, the texture of an opaque object can affect its reaction to light and sound. Rougher textures tend to scatter light and sound waves, while smoother textures tend to reflect them more directly. This can result in different levels of absorption and reflection of light and sound.

## How do different materials react to light and sound on opaque objects?

Different materials can react differently to light and sound on opaque objects. For example, metals tend to reflect both light and sound waves very well, while fabrics may absorb more sound waves but reflect more light. The density and composition of the material can also play a role in its reaction to light and sound.