When we place an object above mirror and viewed from side, we see the image to be below the object, as if the reflected light is coming from inside the mirror. From the image above, the light from top gets reflected in front of object. So comparing the image and object, they are perpendicular to ...

In beta decay, a neutron releases an electron and turns into a proton. The inverse happens, though usually not naturally, in positron emission, where a proton emmits a positron and becomes a neutron. As the electron has mass, approximately 1/1836th of a proton, I was wondering, for how long this ...

I've been wondering: why is the electrical conductivity of a given material defined as the inverse of its electrical resistivity? In other words, why is $$ \sigma \equiv \frac{1}{\rho}~?$$ It indeed makes sense to define a number called conductivity such that, when the resistivity of the material...

In the action term for Majorana fermion as given in Peskin and Schroeder's question 3.4, the first term is : $\int d^4x \space\chi^\dagger i \bar{\mathbb{\sigma}} \cdot \partial\chi$ which can be written as $\int d^4x \space \chi^\dagger i \bar{\mathbb{\sigma}}^\mu \partial_\mu \chi$ where $\bar{...

I have a cylindrical permanent magnet with uniform magnetization $\mathbf{M}=\mathbf{a_z}M$, length $L$ and Diameter $D$. I also have the following expressions for the magnetic flux density and magnetic field intensity inside the magnet. $$\mathbf{B}(z)= \frac{\mu_0M}{2} \Bigg[ \frac{z+ \frac{L}...