Try This
Try answering the following four questions.  The final answers for most of the questions are included behind the question.

 


1. A student conducts a Millikan oil drop experiment.  The device used has parallel plates that are 5.00 mm apart.  The student determines that the mass of the drop is 2.90×10-15 kg.  The student measures how the voltage affects the upward acceleration of the drop.  The measurements are listed below.

Voltage (V)

Acceleration Upward (m/s2)

0

-9.81

100

-5.40

200

-0.98

300

3.43

400

7.85

500

12.26

  1. What are the manipulated and the responding variables?

  2. Draw a graph of the results.

  3. Use the graph to determine the voltage when the electric force and the force of gravity are balanced.

  4. Use your value from c. to determine the charge on the drop.

  5. How many excess electrons are on the drop?

 

2. An oil droplet with a mass of 7.20 × 10-16 kg is moving upward at a constant speed of 2.00 m/s between two horizontal charged plates.  If the electric field strength between the plates is 2.20 × 104 V/m, what is the charge on the oil droplet? (3.21 × 10-19 C)
 

3. An oil droplet with a mass of 3.50 × 10-15 kg accelerates downward at a rate of 2.50 m/s2 when it

is between two horizontal charged plates that are 1.00 cm apart.  Assuming that the excess charge on the droplet is negative and the top plate is positive, how many excess electrons does the droplet carry if the potential difference between the plates is 533 V? (3 e)

 

4. An oil droplet with a mass of 5.70 × 10-16 kg accelerates upward at a rate of 2.90 m/s2 when it is between two horizontal charged plates that are 3.50 cm apart.

  1. Draw a free-body diagram of the forces acting on the oil drop.

  2. If the potential difference between the plates is 792 V, what is the charge of the droplet? (3.20 × 10-19 C)