Final answer:
The electric force on the plastic ball can be determined using the equilibrium condition, equating the horizontal component of the gravitational force to the electric force. The formula Felec = m*g*sin(θ) is used with the given mass, gravitational acceleration, and angle.
Step-by-step explanation:
To calculate the magnitude of the electric force Felec acting on a plastic ball in an electrical experiment, we can use the equilibrium condition where the electrical force is balanced by the component of the gravitational force along the horizontal direction.
The ball makes a 15.0° angle with the vertical when in equilibrium. The tension in the string provides the centripetal force which has both vertical and horizontal components. The vertical component balances the gravitational force, while the horizontal component equals the electric force exerted by the charged rod.
Let's denote the mass of the plastic ball as m, the gravitational acceleration as g, and the angle with the vertical as θ. The gravitational force Fgrav is mg, and its horizontal component is mg sin(θ), which will be equal to Felec.
Therefore, the magnitude of the electric force is calculated as:
Felec = mg sin(θ).