Question

I. The objectives of this lab are (1) to determine initial mechanical energy of a charge (2) to determine final mechanical energy of a charge (3) to prove the law of conservation of energy for the electric charge II. Apparatus(Equipment): Voltage source, measuring tape, smart timer. II. Procedure: A charged body having charge Q = 0.002 C, mass M= 0.004 Kg, was initially held at rest at a voltage line located at height=H=D= 2m. Varying amounts of voltages were applied at the voltage line. The time the charged body took to fall to the zero-voltage level of the ground were measured using a digital smart timer. Attracted by the electrical force, the charge falls to the zero-voltage ground in the indicated times. Since the electrical forces on the charge are stronger than gravity, gravitational forces are negligible. IV. Raw Data: The voltages applied, and the corresponding falling times of the charged particle are indicated in the raw data table below Voltage (V) Time (s) Initial Mech. Energy (E) (Joules) Acceleration(m/s2) Final Mech. Energy (Ec)(Joules) 200 0.280 0.4 50 0.392 400 0.191 0.8 100 0.7296 600 0.165 1.2 150 1.225 800 0.149 1.6 200 1.776 1000 0.132 250 2.178 N V. DATA ANALYSIS: (1) For each row, showing your steps on a separate attached paper, calculate the initial mechanical energy (E.) of the charge, the acceleration of the charge and the final mechanical energy (E) of the charge. Fill in your answers in the table. (2) For each row, calculate the percent difference between initial mechanical energy (Ei) and final mechanical energy (Ef).

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Answer 1

1. Electric field is measured by taking negative grad of the voltage, that is. So keeping the distance fixed(here height=2 m) if we increase the voltage at the upper point, E will be more negative, resulting the absolute value of E to increase.

E V

2. Electric force on the charge is product of the electric field and the charge. So obviously if the electric field increases, the electric force the charge experiences will also increase.

3. No, there will be no significant change in the observation data. Though we are neglecting the gravity, the electric permittivity of air is slightly greater than the vacuum(as in moon). Since the data is taken in SI units, there will be a slight change(not significantly) in the observation data table.

4. The possible sources of errors are -

i) Instrumental Errors:- You cannot get rid of this kind of error in an experiment. In each device, used in this experiment (voltage source, measuring tape, smart timer) there will be some error introduced by each of the devices.

ii) Gravity:- One thing, done here is gravity is neglected. Even though due to very small mass(resulting very less gravitational force) and high voltage (resulting high electric force) the gravitational force can be neglected, it will still introduce some error in the experiment.

iii) Resistance in the line:- Even if a highly conducting line is used there, there will some resistance in it, that will decelerate the mass(not significantly). So the acceleration measured here will change accordingly.