Final answer:
The voltage at a point 3cm from the second plate of a parallel plate capacitor, with the first plate at 300V and the second at -100V, is 200V.
Step-by-step explanation:
The question asks for the voltage at a point within a parallel plate capacitor. The capacitor's first plate is at 300V, and the second plate is at -100V, with a separation of 4cm between them. To find the voltage at 3cm from the second plate, we can use the concept of a uniform electric field in a parallel plate capacitor and the linear relationship between the electric field (E), the potential difference (V), and the distance (d).
The voltage difference across the entire capacitor is 300V - (-100V) = 400V, and the total separation is 4cm. From the second plate (at -100V) to the point 3cm away, 75% of the total distance is covered, therefore 75% of the total voltage difference is dropped across this distance. Thus:
Voltage drop = 0.75 × 400V = 300V.
The voltage at the point 3cm from the second plate (at -100V) is:
V = -100V + 300V = 200V.