"Wisdom begins in wonder" – Socrates
Tag: Physics
Cutoff frequency
08/14/17
“What is the frequency that causes machines to stop working efficiently?”
Many modern electrical machines depend on a frequency for some input. However, sometimes we don’t want it to be accessible to all inputs. To achieve this, we implement something called a cutoff frequency into the system. A cutoff frequency is the frequency point in which a machine’s output will stop working efficiently.
A visualization of reversible vs nonreversible processes
08/08/17
“What exactly is the difference between reversible and non-reversible systems?”
Reversible and non-reversible systems are two of the most fundamental and confusing concepts in thermodynamics. But this visualization should help clarify them. Let’s take a ping pong game. If we are playing without score, then after a round is over, everything goes back to normal with no change in the system, making it reversible. However, if we are keeping score, then after every round the number of points change forever, making this process non-reversible!
Processes
08/07/17
“What do we call it when a system’s state changes?”
Thermodynamic systems have a variety of properties, ranging from temperature to pressure to volume, which all make up its state. However, these properties are subject to change if the system is not in equilibrium. So what do we call this change in properties? Well, after much investigation, thermodynamicist have come up with the term process to describe this change. Processes can be of many types, such as changes in volume or pressure.
Homogeneous and heterogeneous systems
07/21/17
“How do we classify thermodynamic systems?”
Engineering thermodynamics looks at heat, energy, and matter from a macroscopic, or non-atomic perspective. Because of this, objects and materials such as air appear to be uniform in composition. As a result, systems such as these are classified as homogeneous systems. Homogeneous systems stand in direct contract with heterogeneous systems such as a human body (which is composed of many different macroscopic layers). When working out thermodynamics problems, it is extremely important to know if your system is homogeneous or heterogeneous.
Using infrared sensing to see through objects
07/06/17
“Can we see through objects using infrared sensors?”
Wouldn’t it be cool if we could see through objects without X-rays? It would be really useful for applications such as scientific research and security, and we would not have to deal with harmful radiation. Luckily, Scientists and Engineers have discovered that some objects such as shopping bags that are opaque in the visible spectrum are actually transparent in the infrared spectrum!
Electromagnetic propulsion
07/02/17
“How can we make propulsion without fuel?”
As it stands, the vast majority of propulsion machines are based upon fuel combustion technologies. However, this approach is costly, wasteful, and dangerous. So how could we make a new propulsion approach that requires no fuel? Well, let’s use our scientific mindset to find out. We know that when an electric current passed through a conductive material immersed in a magnetic field, it will experience a Lorentz force. So what if we were to use this force to cause objects to move? This is the fundamental idea behind electromagnetic propulsion, and can be used to power machines ranging from linear motors to the astronomical electromagnetic propulsion drives!
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?
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.
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.
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