294 views

### SI Base Unit definition of mass - obsolete?

According to the formal definition of the SI Base unit of mass, the kilogram, it is stated that "The kilogram is the unit of mass; it is equal to the mass of the international prototype of the ...
404 views

### How accurately can you count electrons?

I read that with modern technology they can now shoot one electron at a time. Can you tell me how accurately it is possible to count charges, how it is made and how they did this in the past? How ...
338 views

### How explain this perturbing equation about the 43 arcseconds?

The planetary orbits have been studied as ellipses but the solar system is in motion in relation to the distant stars. Their path is along the tip of an helix and the ecliptic plane is a convenient ...
1k views

### What is a base unit in the new SI, and why is the ampere one of them?

One question that comes up pretty much always in introductory electromagnetism courses is Why the base unit of electrical measurements is the ampere and not the coulomb, and the usual answer is that ...
2k views

### How is the constant of the Biot-Savart Law derived?

In my A-level textbook there is no explanation regarding how the constant in the Biot-Savart law is derived! So how is the constant, $k =\frac {\mu_0}{4\pi}$ derived, and what's the intuition behind ...
539 views

### There are plans to develop a better definition of a “second”. How does the current definition fall short?

The current definition of a second is stated here and I found a presentation on the BIPM site which discusses plans to change to a "better" definition of a second. You can find the presentation here. ...
201 views

### How can a Lego version of a Kibble balance measure the Planck constant?

As the picture shows below [][1] in a Kibble balance, one can drop out the measurement uncertainty of $B$ (magnetic flux intensity) and $L$ (length of coil) by the use of two modes, force mode and ...
193 views

### Is absolute zero still 0 Kelvin?

Following the recent decision to change the definition of SI units, I understand that Kelvin is no longer defined in terms of the number 1/273.16. Does that mean that absolute zero is no longer ...
1k views

### Magnetic effect on AC circuits?

We know that when currents in two wires move parallel to each other, they attract each other and if they are moving anti-parallel to each other, they repel each other but we cannot observe this in ...
81 views

### What is the mass of $N_A$ atoms of carbon-12?

With the recent redefinition of the kilogram, what is the mass of $N_A$ (Avogadro's constant) of carbon-12 atoms? $N_A$ was defined as exactly 6.02214076×$10^{23}$ atoms. Then how close would the ...
111 views

### Why is the kilogram the last SI unit which is defined in terms of a physical prototype? [duplicate]

All elementary SI units, except the kilogram, have been redefined depending of a physical constant. However kilogram still depends on the International Prototype Kilogram. Why is this? Is there no ...
111 views

### Why is the kilogram defined using Earth's gravity? [closed]

Since there are variations of $g$ depending on location on Earth's surface, why not use a reproducible lab experiment using a vertical axis centrifugal balance, and say that one kg is defined by ...
141 views

### How is a Kibble balance used in the new definition of the kilogram, and what's the connection between the balance and Planck's constant? [duplicate]

The BBC News article Kilogram gets a new definition says: How does the new system work? Electromagnets generate a force. Scrap-yards use them on cranes to lift and move large metal objects, ...
I am specifically interested in the following constants because being a student these are some of the most common constants that I face: $R$ (universal gas constant) Stefan constant Permeability of ...