Diagnostic questions about photons

What the Activity is for

Diagnostic questions exploring the understanding of lighting as a stream of photons.

The diagnostic questions can be used for two main purposes:

• to encourage students to talk and think through their understandings of the light as photons model
• to provide the teacher with formative assessment information about the students' understandings of light as photons.

What to Prepare

• printed copies of simple questions on photons (see below)

What Happens During this Activity

It would be a good idea to get the students to work in pairs on these questions, encouraging them to talk through their ideas with each other. Collect responses from all of the pairs and discuss as a whole class.

Alternatively, the questions might be set for homework prior to the lesson, so that you have time to read through the responses.

Question 1: Two light sources give out identical beams of red light. The supply to one of the sources is turned up to increase the brightness of the beam. The source with the brighter beam gives out:

1. the same number of photons/second of higher frequency.
2. more photons/second of the same frequency.
3. more photons/second of higher frequency.
4. more photons/second of lower frequency.

Answer 2. Identical beams means same frequency. A brighter beam means more photons/second.

Question 2: Ultraviolet light causes sunburn of the skin whereas infrared light does not. This is because:

1. the infrared light needs more time to build up sufficient energy to cause sunburn.
2. the infrared photons are bigger than the ultraviolet photons.
3. the ultraviolet photons are bigger than the red photons.
4. the intensity of the infrared light needs to be increased.

Answer 3.

Question 3: When even a very weak beam of blue light is shone on sodium metal, an effect takes place such that electrons are released immediately from the surface of the sodium. This effect must be due to:

1. many relatively low-energy photons arriving each second.
2. a few relatively low-energy photons arriving each second.
3. many relatively high-energy photons arriving each second.
4. a few relatively high-energy photons arriving each second.

Answer 4.