# Determining Planck's Constant [Resolved]

• Hapablap
In summary, the conversation discusses using a graph to determine the value of Planck's constant and provides a calculation that results in a different value than the known value. The suggestion is to use the slope of the line on the graph for more accurate results.
Hapablap
*Edit: Nevermind, I realize where I went wrong!

## Homework Statement

The following graph shows the kinetic energy of the most energetic photoelectrons as a function of the frequency of light falling on the cathode in a photoelectric cell.

http://img208.imageshack.us/img208/3421/fwby.jpg

Use the graph to determine the value of Planck's constant.

E = hf
h = E/f

## The Attempt at a Solution

I'll choose the point where E = 3.0 eV and f = 10.0 Hz for my calculation.

First I'll convert eV to Joules:
3.0 eV x (1.60 x 10^-19 J / 1 eV) = 4.8 x 10^-19 J

Now the calculation:
h = E/f
h = (4.8 x 10^-19 J) / (10.0 x 10^14 Hz)
h = 4.8 x 10^-34 J(s)

We already know that the value of Planck's constant is 6.63 x 10^-34 J(s), so my answer is off.

Any suggestions?

Last edited by a moderator:
looks like you need the slope of the line but what you calculated was the slope of the line going thru 0,0

## 1. What is Planck's constant?

Planck's constant, denoted as h, is a physical constant that relates the energy of a photon to its frequency. It is a fundamental constant in quantum mechanics and is named after its discoverer, Max Planck.

## 2. How is Planck's constant determined?

Planck's constant can be determined experimentally using a device called a "blackbody radiator" which produces thermal radiation. By measuring the frequency and energy of the emitted radiation, scientists can calculate the value of Planck's constant.

## 3. Why is Planck's constant important?

Planck's constant plays a crucial role in understanding the behavior of subatomic particles and their interactions. It is used in various equations and formulas in quantum mechanics, including the famous equation E=hv which relates the energy of a photon to its frequency.

## 4. What is the value of Planck's constant?

The value of Planck's constant is approximately 6.626 x 10^-34 joule seconds (J·s). It is a very small number, but it has a significant impact on the behavior of particles at the quantum level.

## 5. Can Planck's constant change?

According to current scientific understanding, Planck's constant is a fundamental constant and does not change. It is a universal constant that is the same for all observers, regardless of their location or motion.

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