# The Photoelectric Effect: Physics Lab Video

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• 0:03 What is the…
• 0:39 Photoelectric Effect Lab Steps
• 1:26 Data Analysis
• 2:38 Lesson Summary
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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

After watching this lesson, you will be able to explain what the photoelectric effect experiment is, what the results were, and what this tells us about light in terms of wave-particle duality. A short quiz will follow.

## What is the Photoelectric Effect?

Light is a wave. But light also contains particles. In the 18th century, we had already shown that light can act like a wave -- we noticed that light reflects, refracts and diffracts. That part was relatively easy.

But then Albert Einstein noticed a situation where light behaved like a particle. This was his photoelectric effect experiment. It involved shining light onto some metal and noticing that electrons were ejected. Today, we're going to talk about the details of that experiment and what it told Einstein about light.

## Photoelectric Effect Lab Steps

Here are the steps Einstein had to take in his experiment.

Step 1: Create a circuit that contains two large parallel plates that aren't touching.

Step 2: Connect a voltmeter and ammeter to the circuit. The values on the voltmeter and ammeter should read zero initially.

Step 3: Shine monochromatic (single wavelength/single color) light on one of the metal plates.

Step 4: Watch as sparks jump across the 'spark gap' between the plates, completing the circuit.

Step 5: Measure the current and voltage that now exists in the circuit.

Step 6: Try the experiment with different colors and intensities of light and note down your results.

## Data Analysis

In completing his experiment, Einstein found that electrons were ejected. Brighter light caused more electrons to be ejected, but it didn't cause those electrons to move any faster. But when he increased the energy of the light (by using bluer light) the ejected electrons WERE faster. This was a big surprise to him. And these observations led him to conclude that light behaves as BOTH a particle AND a wave. This is called wave-particle duality.

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