State Coulomb’s law of force between charges - Leaving Cert Physics - Question 9 - 2007

To give an electroscope a positive charge, follow these steps:

1. Take a charged rod (which is negatively charged) and bring it close to the cap of the electroscope without touching it.
2. The negative charge on the rod will repel the electrons in the electroscope downwards.
3. While the rod is still near, touch the cap with your finger. This allows electrons to leave the electroscope to the ground.
4. Remove the charged rod first and then the finger. Now the electroscope will have a net positive charge.

When the cap of an electroscope is earthed, the charge on the electroscope dissipates. This happens because the earth acts as a reservoir of charge, allowing excess electrons to flow into the ground. As a result, the leaves of the electroscope will hang down since there is no longer an electrostatic repulsion due to the removed charge.

The cap of the electroscope can be earthed by touching it with a finger or connecting it to the ground using a conductive material. This allows charges to flow freely between the electroscope and the earth.

When the switch is in position A, the capacitor charges up. The current from the battery flows into the capacitor, storing electrical energy in the form of an electric field between its plates.

When the switch is moved to position B, the capacitor discharges. This creates a current that flows through the bulb, causing it to light up briefly as the stored energy in the capacitor is released.

The capacitance $C$ can be calculated using the formula:

$C = \frac{Q}{V}$

where $Q$ is the charge and $V$ is the voltage. Here, $Q = 0.6 C$ and $V = 6 V$. Therefore, substituting the values:

$C = \frac{0.6}{6} = 0.1 \text{ F}$

Capacitors are used to store energy in electronic circuits. For instance, they can store electrical energy to smooth out voltage fluctuations in power supply circuits or to filter signals in radio and audio devices.