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## electric field

### 2. Series 9. Year - 4. electrical cube

Imagine a cube with an electrical charge uniformly distributed with density $ρ$ in the whole volume. The intensity of electrical field in point $A$ is $\textbf{E}$. But what will be its value when we cut out a small cube of half the size of the original one (see pic. 3)?

### 1. Series 9. Year - 3. plate capacitor

A capacitor formed by two parallel metal plates of area $S$ each placed in a distance $l_{1}$ one from another are charged at the voltage $U_{b}$. What work must be performed to move the plates apart to distance $l_{2}$, if we

- had disconnected,
- hadn’t disconnected

the battery..