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

To give an electroscope a positive charge, take a charged rod (which is positively charged) and bring it close to the cap of the electroscope without touching it. This will cause electrons in the electroscope to be repelled down into the metal rod, leaving the electroscope positively charged. Remove the charged rod while holding the electroscope, ensuring that contact is not made during this process.

When the cap of the electroscope is earthed, you observe that the leaves of the electroscope collapse and return to a neutral position. This happens because the positive charge is neutralized as electrons flow from the earth through the grounding connection into the electroscope, causing it to lose its charge.

The cap of the electroscope is earthed by touching it with a conductive material that is connected to the ground. This allows the charge to flow from the cap to the ground, neutralizing it.

When the switch is in position A, the capacitor is charging from the battery. As current flows into the capacitor, it accumulates charge until it reaches the maximum voltage that the battery provides.

The bulb lights up in position B because the circuit is now completed, allowing the stored charge in the capacitor to discharge through the bulb, providing it with electrical energy which lights it momentarily.

The capacitance, C, can be calculated using the formula: $C = \frac{Q}{V}$
Where Q is the charge and V is the voltage. Here,
$C = \frac{0.6 \, C}{6 \, V} = 0.1 \, F$

Capacitors are commonly used to store charge in electronic devices, smooth out fluctuations in power supply (filtering), and in timing applications in circuits.