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Define capacitance - Leaving Cert Physics - Question d - 2008
Question d
Define capacitance. Describe how an electroscope can be charged by induction. How would you demonstrate that the capacitance of a parallel plate capacitor depends ... show full transcript
Worked Solution & Example Answer:Define capacitance - Leaving Cert Physics - Question d - 2008
Step 1
Define capacitance.
Answer
Capacitance is defined as the ratio of electric charge (Q) stored on a conductor to the potential difference (V) across it. Mathematically, this is represented as:
Where:
- is the capacitance measured in farads (F).
- is the charge in coulombs (C).
- is the voltage in volts (V).
Step 2
Describe how an electroscope can be charged by induction.
Answer
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Charged Object Adjacent to Electroscope: Place a charged object close to the electroscope without making contact. The presence of the charged object induces a separation of charges within the electroscope.
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Earth Electroscope (Briefly): Briefly earth the electroscope by touching it with a finger. This allows electrons to either leave or enter the electroscope, depending on the charge of the external object.
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Remove Charged Object: After earthing, remove the charged object. The electroscope will retain a net charge due to the induced charge distribution, and this can be observed via the divergence of the leaves.
Step 3
How would you demonstrate that the capacitance of a parallel plate capacitor depends on the distance between its plates?
Answer
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Arrangement: Connect a digital multimeter with a capacitance setting to measure the capacitance between the plates of the capacitor.
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Method: Switch on the meter to obtain an initial reading of the capacitance at a certain distance.
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Slowly Separate Plates: Gradually increase the distance between the plates while continuing to monitor the capacitance reading.
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Observation: As the plates are separated, the capacitance (reading) will decrease, indicating an inverse relationship between the capacitance and distance between the plates.