Examples of conductive medium in the following topics:
-
- The firing of neurons in your brain is also an example of electric current - that is, the movement of electric charge through a conductive medium.
- The flow of electricity requires a medium in which charge can flow .
- We call an object or medium that allows charge to flow a conductor, while the empirical measure of a material's ability to conduct charge is called the electrical conductance.
- The SI unit for conductance is the siemens (S).
- An object or medium that has high electrical resistance is called a resistor.
-
- For example, suppose we have a conducting medium so that the current density j is related to the electric field E by Ohm's law: ${\vec j} = \sigma {\vec E}$ where $\sigma$ is the conductivity (cgs unit = sec$^{-1}$.
- Investigate the propagation of electromagnetic waves in such a medium and show that:
- Consider a charge $Q$ in a viscous medium where the viscous force is proportional to velocity:
- Suppose a circular polarized wave passes through the medium.
-
- A laser consists of a gain medium, a mechanism to supply energy to it, and something to provide optical feedback.
- When a gain medium is placed in an optical cavity, a laser can then produce a coherent beam of photons.
- The gain medium is where the optical amplification process occurs.
- The most common type of laser uses feedback from an optical cavity--a pair of highly reflective mirrors on either end of the gain medium.
- A single photon can bounce back and forth between the mirrors many times, passing through the gain medium and being amplified each time.
-
- Refraction is a surface phenomenon that occurs as the change in direction of a wave due to a change in its medium.
- Refraction is the change in direction of a wave due to a change in its medium.
- Due to change of medium, the phase velocity of the wave is changed but its frequency remains constant (most commonly observed when a wave passes from one medium to another at any angle other than 90° or 0°).
- Refraction of light is the most commonly observed phenomenon, but any type of wave can refract when it interacts with a medium (e.g., when sound waves pass from one medium into another or when water waves move into water of a different depth).
- In optics, refraction is a phenomenon that often occurs when waves travel from a medium with a given refractive index to a medium with another at an oblique angle.
-
- The Doppler Effect is the change in a wave's perceived frequency that results from the source's motion, the observer, and the medium.
- Finally, if the medium through which the waves propagate moves, the Doppler effect will be noticed even for a stationary observer.
- Quantitatively, the Doppler effect can be characterized by relating the frequency perceived (f) to the velocity of waves in the medium (c), the velocity of the receiver relative to the medium (vr), the velocity of the source relative to the medium (vs), and the actual emitted frequency (f0):
-
- Apparatus: A hologram can be made by shining part of the light beam directly onto the recording medium, and the other part onto the object in such a way that some of the scattered light falls onto the recording medium.
- Some of the light scattered (reflected) from the scene then falls onto the recording medium.
- Several different materials can be used as the recording medium.
- Process: When the two laser beams reach the recording medium, their light waves intersect and interfere with each other.
- It is this interference pattern that is imprinted on the recording medium .
-
- Yet the space between Earth and the Sun is largely empty, without any possibility of heat transfer by convection or conduction.
- The hot body emits electromagnetic waves that are absorbed by our skin, and no medium is required for them to propagate.
- Convection transfers energy away from the observers as hot air rises, while conduction is negligibly slow here.
-
- Conduction is the transfer of heat through stationary matter by physical contact.
- Some materials conduct thermal energy faster than others.
- Fluids and gases are less conductive than solids.
- Heat conduction occurs through any material, represented here by a rectangular bar.
- The rate of heat transfer by conduction is directly proportional to the surface area A, the temperature difference T2−T1, and the substance's conductivity k.
-
- When the medium changes, a wave often experiences partial transmission and partial refection at the interface.
- When the medium through which a wave travels suddenly changes, the wave often experiences partial transmission and partial refection at the interface.
- Reflection is a wave phenomenon that changes the direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated.
- k1 and k2 are determined by the speed of the wave in each medium.
- A wave experiences partial transmittance and partial reflectance when the medium through which it travels suddenly changes.
-
- For a fluid at rest, the conditions for static equilibrium must be met at any point within the fluid medium.
- Similarly, the sum of the forces and torques of an object at rest within a static fluid medium must also be zero.
- In considering a stationary object within a liquid medium at rest, the forces acting at any point in time and at any point in space within the medium must be analyzed.
- In analyzing such a simple system, consider a rectangular region within the fluid medium with density ρL (same density as the fluid medium), width w, length l, and height h, as shown in .
- Next, the forces acting on this region within the medium are taken into account.