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Found in: Page 92

### Modern Physics

Book edition 2nd Edition
Author(s) Randy Harris
Pages 633 pages
ISBN 9780805303087

# You are conducting a photoelectric effect experiment by shining a light of 500 nm wavelength at a piece of metal and determining the stopping potential. If, unbeknownst to you, your 500 nm source actually contained a small amount of ultraviolet light, would it throw off your results by a small amount, or by quite a bit? Explain.

Yes, the presence of ultraviolet light affects the result by quite a bit as more stopping potential would be required than the one designed for 500 nm light to stop the current.

See the step by step solution

## Step 1: Given data

The presence of a small amount of ultraviolet light in light of wavelength is 500 nm.

## Step 2: Concept used

Thermal equilibrium: It is a state of equilibrium in which the temperature of both the objects becomes the same and there is no further transfer of heat.

Electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field propagating through space, carrying electromagnetic radiant energy.

## Step 3: Light Nature

Light of wavelength, 500 nm is incident on a metal surface. The stopping potential is determined for the photoelectric effect setup. A small amount of ultraviolet light is also present in the light source.

## Step 4: Photoelectric effect

For the photoelectric effect to take place, the wavelength of the incoming light must be greater than that of the threshold wavelength for the given metal. When the wavelength is more than the threshold wavelength, then photoelectrons will be emitted and photocurrent will flow in the circuit. To stop the photocurrent, we apply a certain potential difference across the plates which doesn't allow the electrons to leave the collector plate. This potential difference is called the stopping potential.

## Step 5: Intensity of light

The emission of electrons doesn't depend on the intensity of light but only depends on the wavelength of the light. Since the wavelength of ultraviolet light is less than that of 500 nm light, the emission will occur at the potential difference designed for the 500 nm light.

Therefore, the presence of even a small amount of ultraviolet light (low intensity) will affect the result significantly as this will require more stopping potential than the one designed for 500 nm light.