If on the $x$-axis electric potential decreases uniformly from $60 \,V$ to $20 \,V$ between $x=-2 \,m$ to $x=+2 \,m$, then the magnitude of electric field at the origin

$A, B$ and $C$ are three points in a uniform electric field. The electric potential is

In a certain reglon of space with volume $0.2\, m ^{3}$ the electric potential is found to be $5\, V$ throughout. The magnitude of electric field in this region is ______ $N/C$

Electric potential at any point is $V = -5x + 3y + \sqrt {15} z$, then the magnitude of the electric field is

A uniform electric field having a magnitude ${E_0}$ and direction along the positive $X - $ axis exists. If the potential $V$ is zero at $x = 0$, then its value at $X = + x$ will be

A cathode ray tube contains a pair of parallel metal plates $1.0\, cm$ apart and $3.0\, cm$ long. A narrow horizontal beam of electron with a velocity $3 \times 10^7\, m/s$ passed down the tube midway between the plates. When a potential difference of $550\, V$ is maintained across the plates, it is found that the electron beam is so deflected that it just strikes the end of one of the plates. Then the specific charge of the electron in $C/kg$ is