Determining Planck's Constant

The Determining Planck's Constant apparatus is designed to determine Planck's constant by studying the photoelectric effect using light-emitting diodes (LEDs) of different wavelengths. Light from each LED is directed onto the photocathode of a vacuum photocell, while the stopping voltage is varied and the resulting photocurrent is measured with high sensitivity. Software-based data acquisition enables automatic recording and analysis of the characteristic curves for accurate determination of Planck's constant. Manufactured by Atico Export India.

Principle

The experiment is based on the photoelectric effect. Monochromatic light from LEDs of different wavelengths illuminates the photocathode of a vacuum photocell, causing photoelectrons to be emitted. A variable opposing voltage is applied between the cathode and anode, and the resulting photocurrent is measured using a high-sensitivity picoampere sensor. By analyzing the stopping voltage corresponding to different wavelengths, the relationship between photon energy and electron emission is established, allowing the determination of Planck's constant.

Objectives

• Determine Planck's constant using the photoelectric effect.
• Study the relationship between light wavelength and stopping voltage.
• Measure the photocurrent generated by different monochromatic light sources.
• Analyze the characteristic curves of a vacuum photocell.
• Verify the principles of quantum theory.
• Understand the photoelectric effect using LED light sources.

System Components

Table Housing with Photocell :

• Quantity: 1

LED with Holder :

• Wavelength: 375 nm
• Quantity: 1

LED with Holder :

• Wavelength: 400 nm
• Quantity: 1

LED with Holder :

• Wavelength: 435 nm
• Quantity: 1

LED with Holder :

• Wavelength: 505 nm
• Quantity: 1

LED with Holder :

• Wavelength: 545 nm
• Quantity: 1

Voltage Source :

• Output: -5 to +5 V
• Current: 0.1 mA
• Quantity: 1

USB Cable :

• USB Type-A to Mini-USB
• Quantity: 2

USB Plug-In Power Supply :

• Output: 5 V DC
• Quantity: 1

pA Sensor :

• Quantity: 1

Data Acquisition Interface :

• Quantity: 1

Data Analysis Software :

• Quantity: 1

BNC Cable :

• Length: 1 m
• Quantity: 1

Connecting Leads :

• Current Rating: 19 A
• Length: 50 cm
• Red/Blue Pair
• Quantity: 2