WHAT IS MILLIKANS OIL DROP EXPERIMENT ?

Introduction

This tutorial explains Millikan's Oil Drop Experiment, a significant scientific milestone that determined the charge and mass of an electron. Conducted by Robert Millikan in 1910, this experiment helped to confirm the existence of subatomic particles and contributed to our understanding of atomic structure. Here, you will learn the steps of the experiment, its methodology, and its implications in the field of physics.

Step 1: Understand the Experiment's Purpose

• The primary aim of Millikan’s Oil Drop Experiment was to measure the charge of the electron.
• This experiment provided evidence for the quantization of electric charge, which means that electric charge exists in discrete units rather than a continuous range.

Step 2: Set Up the Apparatus

• Materials Needed:

  • A vacuum chamber to reduce air resistance.
  • An oil spray to create tiny droplets.
  • An electric field apparatus to apply a voltage across the chamber.
  • A microscope to observe the oil droplets.

• Procedure:

  1. Create a fine mist of oil droplets using an atomizer.
  2. Allow the droplets to fall into the vacuum chamber.
  3. Use a microscope to focus on individual droplets as they descend.

Step 3: Ionize the Air

• Use X-rays to ionize the air inside the chamber:
  • When the X-rays pass through the air, they collide with air molecules, knocking electrons loose and creating positive ions.
  • These free electrons attach to the oil droplets, imparting a negative charge to them.

Step 4: Apply the Electric Field

• Once the oil droplets are charged, apply an electric field:
  • Adjust the voltage across the plates in the chamber.
  • The electric field will exert a force on the negatively charged oil droplets, causing them to rise or fall depending on the strength of the field.

Step 5: Observe and Measure

• Carefully observe the behavior of the charged droplets:
  • When the electric force balances the gravitational force, the droplet will remain suspended in the air.
  • Measure the voltage needed to achieve this balance.

Step 6: Calculate the Charge

• Use the following formula to calculate the charge on the oil droplets:

  [ q = \frac{mg}{E} ]

  Where:

  • ( q ) = charge of the electron
  • ( m ) = mass of the droplet (determined from its size)
  • ( g ) = acceleration due to gravity
  • ( E ) = electric field strength (voltage divided by distance between plates)

Conclusion

Millikan's Oil Drop Experiment was a groundbreaking study that provided crucial insights into the structure of the atom and the properties of electrons. By following these steps, you can appreciate the experimental setup and calculations that led to the determination of the electron's charge and mass. Understanding this experiment is foundational for further studies in physics and chemistry.