- Place it mid-way between the plates and move it across the plates.
The deflection remains the same except that the deflection decreases near the edge of the
plates.
- Move it parallel to the electric field.
The deflection remains the same.
- Move it very close to the plates.
The deflection increases slightly since the charge on the foil attracts those of opposite
charge onto the part of the plate opposite to it.
(d) Move it around between the metal plates to explore the electric field.
The deflection remains the same in all directions since the electric force on the foil and
hence the electric field remain constant.
7. Place the foil mid-way between the plates, and change the voltage across the plates. Describe how the voltage affects the deflection of the foil.
Increase in the voltage will increase the electric field between the plates and hence the
electric force on the foil.
8. Fix the voltage across the plates, vary the separation between the two plates. Describe how the separation affects the deflection of the foil.
The deflection decreases as the separation increases since the electric field is weaker.
9. Place the two metal plates 4 cm apart, and adjust the voltage until the deflection is 45o. Record the voltage across the plates in the table below.
10. Mark the shadow of the foil strip in step 9 on the screen. Then vary the voltage and the separation between the plates simultaneously such that the deflection remains constant. Tabulate the results in the table below.
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Plot the graph of the voltage against the separation (V-d graph).
Find the slope of the graph. What conclusion can you draw from the graph?
The slope is 0.38 kV / cm, which denotes the strength of the electric field between the
plates.
Results and Discussion
- What factors can affect the electric field between the metal plates?
The separation between the plates and the voltage affect the electric field between the
plates.
- In step 9, if we keep the voltage across the metal plates constant and interchange the polarity of the metal plates, what happens to the foil?
The foil deflects at the same angle but towards the opposite side, i.e. the negative plate.
- State the sources of error and suggest improvements for this experiment.
In order to get the accurate deflection angle of the foil, the translucent screen should be
placed perpendicular to the metal plates, and the foil is free to turn about the pin towards
the sides of the metal plates without any friction.
- Give a conclusion to this experiment.
(a) Uniform electric field is produced in between the plates when a voltage is applied.
(b) The separation between the plates and the voltage affect the electric field.
(c) The electric field in between the metal plates was found to 0.38 kV / cm, such that the
foil deflects at about 45o.
New Way Physics for Advanced Level
