Category: Physics

Valence gap

Valence gap

Valence gap

06/05/17

“Why are materials electrically insulative, conductive, or semiconductive?”

 

All materials fall into one of three classifications when it comes to moving an electric current, insulative, conductive, or semiconductive. However, what property determines this? Well, let’s look at the atomic level to find out. When multiples atoms come close together, their possible energy states branch out into multiple bands. The two most important bands are the valence (which holds the outermost electrons) and conduction bands (which holds electrons ready to conduct) These bands will be separated by a valence gap.. If there is no difference, then it takes no extra energy to conduct energy and the material is conductive. If there is a noticeable but surmountable gap then the material is semiconductive. And if it is impossible to reach then it is insulative. You can think of it like the distance to a basketball hoop, the higher the height the more energy is required.

What happens when two lenses are placed together?

What happens when two lenses are placed together?

What happens when two lenses are placed together?

05/15/17

“How do we solve a physics problem with two lenses placed together?”
When doing a geometric optics problems, we often assume the lenses to be discrete from one another. However, what happens when we have two lenses right next to each other? Well, let’s think about it using our mathematical mindset. If we look carefully, then we will notice that the same amount of light will be incoming and outgoing for both sides. This is similar to how the voltage drop on two parallel resistors is the same. So what if we were to treat our optical system in a similar manner? Well, after much research into this matter, opticists have shown that both lenses can be replaced with an equivalent lens with a focal length given by the equation 1/f_combined=1/f1+1/f2.

Concave mirrors

Concave mirrors

Concave mirrors

05/14/17

“How does a mirror that bends inwards behave?”
Mirrors come in all different shapes and sizes. Some are straight like a piece of paper, some bend outwards, some inwards. However, what are some of the defining physical characteristics of mirrors? Well, let’s analyze it with our scientific mindsets. When an object is beyond the center of curvature, then an image real, inverted, and minimized will be produced. If the object is at the center of curvature, then a real inverted image of equal size will be produced. If the image is between the center length and focal point, then an image real, inverted, and magnified will be produced. If the object is at the focus, then the image will form at – infinity. And if the object is just beyond the focal point, then a magnified virtual image will be formed. Concave mirrors have numerous applications, ranging from the headlights of cars to shaving mirrors and even to visual bomb detectors!

How to calculate change in entropy

How to calculate change in entropy

How to calculate change in entropy

05/13/17

“How can we calculate the change in entropy for a thermodynamic process?”

 

It is well known that for all thermodynamic processes, there is a corresponding increase in entropy in the entire system. However, how can we quantitatively measure such a change? Well, after many years of research, physicists and engineers have been able to come up with an equation which states that the change in entropy for a reversible process is equal to the time integral of change of heat divided by the initial temperature, or (delta)s=integral(dq/T). From this, we can derive that for an isothermal expansion or contraction, the equation will be (delta)S=nRln(vf/v0), and (delta)d=-nRln(pf_p0), while in cooling or heating a system it will be (delta)s=ncln(tf/t0) and for a phase transition it will be (delta)s=(delta)h/T.

Complex fluids

Complex fluids

Complex fluids

05/02/17

“What happens when there is a fluid with more than one phase present?”
Most engineering or physics applications of fluid mechanics deal with only one phase of matter. However, what happens when there is there is a multiphase solution present, such as in shaving cream? Well, after much investigation, engineers and physicists have determined that such materials can not be treated as typical fluids and instead must be classified as complex fluids. Complex fluids exhibit often unusual stress-strain relations, are highly nonlinear, and relatively unknown. Perhaps readers of this blog will pursue research into this subject and illuminate us on this subject.

Adiabatic process

Adiabatic process

Adiabatic process

05/01/17

“Is there a thermodynamic process with no heat exchange?”
When most people think of thermodynamics, one of the first thing that pops into people’s minds is one phenomenon, heat flow. However, is it possible to have such a process with no heat flow? Well, let’s think about it. If we were to take our system and completely isolated it inside an insulator, no heat would be able to flow in or out. Therefore, all of the work done must come from the internal energy. This phenomenon is known an adiabatic process. In an adiabatic process, the pressure multiplied by the volume raised to the ratio of the specific heats of the gas is always equal to a constant (PV^(c_p/c_v)), leading to a steeper PV diagram than the isothermal process.

Isothermal process

Isothermal process

Isothermal process

04/30/17

“Can we have a thermodynamic process in which the temperature of the system remains constant?”
When working with thermodynamic systems, it is very easy for the internal temperature to change when other properties change as well. However, is it possible to have a fixed constant temperature process? Well, let’s think about how this can be accomplished. We know that when a system does work (such as a gas expanding) it will lose some of its internal energy and therefore cooling it. However, if we were to then supply heat to counteract this loss, the temperature would remain consistent, therefore resulting in what engineers and scientists call an isothermal process. In an isothermal gas expansion, the change in volume is directly equal to the number of moles present in the gas times the (fixed) temperature times universal gas constant divided by the change of pressure, which can be summarized symbolically as (Delta)V=nRT/(Delta)P. Isothermal processes are used to study highly structured mechanical systems such as Carnot cycles and chemical reactions.