Two large vertical and parallel metal plates having a separation of 1 cm are connected to a DC voltage source of potential difference X. A proton is released at rest midway between the two plates. It is found to move at 45° to the vertical JUST after release. Then X is nearly
1 × 10–5 V
1 × 10–7 V
1 × 10–9 V
1 × 10–10 V