A rubber belt in an electrostatic machine has a width of 0.1 m and moves with speed 0.4 m s⁻¹ - AQA - A-Level Physics - Question 21 - 2019 - Paper 1

To find the charge collected by the sphere each second, we first calculate the rate at which charge is transferred.

1. The speed of the belt is given as 0.4 m/s. Therefore, the distance covered by the belt in one second is 0.4 m.
2. The width of the belt is 0.1 m.
3. The area of the belt that passes a given point in one second can be calculated as: $Area = Width \times Distance = 0.1 \ m \times 0.4 \ m = 0.04 \ m^2$
4. If each square metre of the belt carries a charge Q, the charge transferred in one second is: $Charge = Area \times Charge \ per \ unit \ area = 0.04 \ m^2 \times Q = 0.04Q$

Thus, the charge collected by the sphere each second is 0.04Q.