Angle of incidence related to the power and the seasons

What the Activity is for

This activity provides an opportunity to show that the explanation for seasons can be confirmed by experimental data gathered from a simple model.

What to Prepare

For each group

• 100 W lamp
• A mounted solar cell
• 4 millimetre leads
• A microjoulemeter
• A protractor
• Graph paper

What Happens During this Activity

You might introduce this an an example of looking for the patterns underlying phenomena and as an example where you build a physical model to see if it can help can interpret the phenomena.

In this experiment, the lamp is used to model the Sun and the solar cell the ground, or surface of the Earth. The angle of the ground is then adjusted and the output of the cell measured. By taking measurements, you can then plot a graph to see what the relationship is, and if it explains the variation of temperature with the seasons.

The previous activity used a theoretical idea to predict that there will be four times less energy per square metre hitting the ground in winter. Is this confirmed when we use a simple model with a bulb as the Sun and a solar cell as the ground?

• Connect the solar cell to the microjoulemeter, set to measure power.
• On a piece of paper, draw a set of lines at suitable angles.
• Set up the lamp no less than 50 centimetre from the solar cell. Try and ensure that it is on the same level as the lamp.
• Place the solar cell at 0 ° to the lamp and take this reading.
• Now mount the template behind the solar cell and tilt it. Take this reading. Repeat for all the other angles.
• Use this to construct a table of readings. In the third column, deduct the 0 ° reading from all the readings to set a baseline.
• Plot the energy received against the angle.

Looking at the graph shows that the energy received at 14 ° (the angle of the Sun above the horizon on 21 December) is about 4 times less than the energy at 67 ° (the angle of the Sun above the horizon on 21 June). Connect this back to the prediction.