Write an expression for the electric field strength $E$ a distance $r$ from a point charge $Q$ in a vacuum. State the name of any other symbol used.
Two point charges A and B are placed a distance $10.0\,\text{cm}$ apart in a vacuum, as shown in Fig. 6.1. A point $P$ lies on the line joining the charges A and B. Point $P$ is a distance $x$ from A. The way the electric field strength $E$ at point $P$ varies with distance $x$ is shown in Fig. 6.2.
State and explain whether the charges A and B have the same sign or opposite signs.
State and explain whether charges A and B have equal magnitudes or different magnitudes.
An electron is placed at point $P$. Without using calculation, state and explain how the magnitude of the electron's acceleration changes as it moves from the position where $x = 3\,\text{cm}$ to the position where $x = 7\,\text{cm}$.