# Tag Info

### Teacher told us we're not allowed to write negative vectors, is this correct or not?

Your teacher is instructing you to define the vectors in terms of their components, \begin{align} \vec F_1 &= \hat x \cdot 20\,\mathrm N \\ \vec F_2 &= \hat x \cdot (-10\,\mathrm N) \end{align}...

### Changing the basis from $p$-basis to $k$-basis in standard quantum mechanics

if $$\hat p = \int dp |p\rangle p \langle p|$$ and I want to chage the basis to $|k\rangle$ it is correct to say that $\hat p$ is therefore equal to:  \hat p = \hbar^2 \int dk |k\rangle k \langle k| ...
1 vote

### Teacher told us we're not allowed to write negative vectors, is this correct or not?

Presumably the teacher is trying to build a good habit of separating the vector from the representation. Vectors and numbers are different types of things. One can represent vectors well using numbers ...
1 vote

### The equipartion theorem and degree of freedom in case of vibration

tldr: Chemists and physicists mean slightly different things by the term "vibrational degrees of freedom". What chemists call a vibrational degree of freedom, physicists call a vibrational ...
1 vote

### Doubt in negative sign of relative velocities of two objects in same directions and opposite directions

First assign a consistent sign convention to your velocities. If A and B are moving in the same direction, assign a positive sign to both of their velocities. If they are moving in opposite directions,...
1 vote
Accepted

### Confusion in definition of Potential Energy

Without writing the explicit meaning of formulae, comments, and answers may only increase the original confusion. The work done by a force ${\bf F}$ when a point-like body is displaced along any path ...
1 vote
Accepted

### Why is there no negative sign in the linear form calculation of voltage but there is a negative in the integral form?

The minus is a reminder of the convention used in electrostatics. When $\nabla \times \vec{E}=0$, $\vec{E}$ is the gradient of a potential and by convention $\vec{E} = -\nabla \phi$. If $\gamma$ is ...
1 vote

### Voltage Difference Across Capacitor Plates

The 9V in "9V battery" typically refers to it's emf, and this would be the potential difference between its ends. Since the potential is defined up to an arbitrary constant, it could mean ...

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