Name:______Date:______Per:______

Effect of Sunlight Angles on the Earth Lab

A typical day in July, in NY, is close to 85oF, while a typical January day in NY is usually around 32oF. This happens even though we are actually several million miles closer to the sun in January than in July!

When light from the Sun hits the Earth directly (overhead), the solar energy is spread over a smaller surface area and is more intense (concentrated) than when light hits the Earth indirectly, at a more slanted angle (less intense).

Scientists often use models to recreate the real world in a laboratory. In this lab, you will use a model to simulate how sunlight strikes the surface of the Earth. You will use a lamp to represent the Sun. You will change the angle at which light strikes a flat surface and see what effect this has on the heating of the surface. This lab will demonstrate how sunlight strikes the surface of the Earth at different angles.

  1. The aim of this investigation is to demonstrate that direct light heats up an area more quickly than indirect light. It is assumed that this experiment will be a teacher led demonstration but with measurements taken by the learners, however, if you have enough equipment there is no reason why the learners cannot set up the experiment themselves. Strip thermometers are often used for taking children's temperatures and are available in most chemists. You can extend this activity if you wish by changing the angle at which the "indirect light" lamp points at the card in steps. Learners should find that shallower angles with respect to the surface produce lower temperature readings.

Ensure that the two lamps have bulbs of the same power installed in them. During the experiment the strip thermometers may become too hot. If this happens turn both the lamps off for about 5 minutes and let them cool down, then start the observation again.

I. Question:Does direct light heat up an area more than indirect light?

II. Hypothesis:(Give the 3 possible predications to the question)

  1. ______
  2. ______
  3. ______

III.Learner-dependent answer. Learners could state 'The direct light will heat the area more quickly.'

Match the MMatch the VARIABLES:

______IV1. Same amount of exposure to the light for each thermometer.

______DV2. The final temperature readings.

______CV3. Angle of the light shone on each thermometer.

______CV4. The same size light bulbs used in each lamp.

IV. The temperature. This is the dependent variable.

Materialsand Procedure

  • two desk lamps
  • two pieces of black paper
  • two thermometers
  • watch or clock
  • marker pen and/or sticker to label the paper

Procedure:

  1. Place the two desk lamps on a table or desk about 1 meter apart from each other.
  2. Point one of the desk lamps directly downwards towards the table, at a height of about 30 cm.
  3. Place the black card under the light and label it "A".
  4. Place the thermometer strip in the center of the black card. The light bulb should be directly above the thermometer.
  5. Adjust the second desk lamp so that it is at the same height as the first one, but instead of pointing it directly down at the table, tilt it slightly to one side (left-right direction).
  6. Place the second piece of black card under this lamp and label it "B".
  7. Place the second thermometer in the center of the black paper. This light should shine indirectly over the thermometer.
  8. Record the temperature of both thermometers in the data table below.
  9. Turn on both lights at the same time. Wait for about 1 minute and then record the temperatures of the thermometers in the table below.

SUNLIGHT LAB DATA TABLE:

Paper / Initial
temperature (°C) / Final
temperature (°C) / Temperature
difference (°C)
Paper A (overhead light)
Paper B (light at slanted angle)

The temperatures recorded are learner dependent. However, all learners should agree on the initial temperature of the thermometers. The thermometers should indicate the same initial temperature if they are calibrated correctly. The final temperature should be higher than the initial temperature, and the temperature of A should be higher than B. They should then work out the temperature difference by subtracting the initial temperature from the final temperature.

Is light hitting the paperfrom lamp A direct or indirect light?

Direct light.

Is light hitting the paperfrom lamp B direct or indirect light?

Indirect light.

Which paperhas the hottest final temperature? Why is this?

Card A, this is because the light is shining directly onto it and so the energy is more concentrated.

Learner-dependent answer. Learners should clearly explain the reasoning behind their answers. Examples could include using more sensitive thermometers, repeating the observations and taking an average value for the temperatures.

CONCLUSIONQUESTIONS:

1.What is the effect of the angle (more direct or indirect) of sunlight on the amount of heat an area receives?

2. Direct light heats the card more quickly as light is more concentrated and so more energy per unit area falls onto the card. This energy is what causes the heating and so if there is more energy per unit area falling on a surface then there will be more heating of that surface.

Imagine that the lamps represent sunlight and the paper represent the surface of the Earth.What season on Earth do you think corresponds to case A, and why do you think this?

  1. 33. Summer because it is warmer.

3. What season on Earth do you think corresponds to case B, and why do you think this?

4.Why do we receive more direct light in summer?

______

5.Why is it warmer at the equator than at the North and South Poles? ______

6. Why do we use sunscreen in the summer but not in the winter? ______

Winter because it is cooler.

Areas of the Earth that are hit by direct sunlight are therefore warmer than areas that are hit by indirect sunlight. In the summer, the Sun is high in the sky and we receive more direct sunlight than in winter when the Sun is lower in the sky and we receive more indirect sunlight. This explains why summer is warmer than winter.

Viewed from the Earth's surface, the Sun appears higher in the sky in summer. As the

Sun travels higher in the sky it takes more time to travel across the sky from sunrise to sunset. Therefore, daytime is longer in summer than in winter. The change in the length of daytime during the year also occurs because of the tilt of the Earth's rotation axis in space.

The apparent path of the Sun across the sky in winter and summer.

The Sun travels higher and further across the sky in summer, and so days are longer.

Remember that it is NOT actually the Sun that moves, but Earth's rotation which makes it look as though the Sun moves across the sky.

The following questions are challenging and can be used to test the most able learners and extend their thinking.

What do you think would happen to the seasons if the Earth were not tilted by 23.5°, but instead were pointed straight up relative to the path of its orbit?

You can discuss this with your class. The Sun's path across the sky would be the same all year round and there would no longer be seasons as we know them. It would still be warm at the equator and cold at the poles however. The biggest impact on temperatures would be at the poles. Presently they have dark winters with extremely low temperatures followed by warmer temperatures and constant light in the summer. If there were no tilt, the polar regions would have much more uniform temperatures all year round and the Sun would always be low on the horizon. Across the Earth it would be like it is in the middle of autumn or spring all year.

There would still be some slight changes during the year. This is because the Earth-Sun distance varies during the year as the Earth's orbit around the Sun is not a perfect circle (it is slightly elliptical). Currently, the Earth is closest to the Sun in January and furthest away in July. With no tilt, this change in Earth-Sun distance during the year would produce a slight impact on the weather pattern. It must be emphasised that the effect would be tiny as the Earth-Sun distance does not vary significantly different during the year (147 million km in January 2013 compared to 152 million km in July 2013).

The Southern Hemisphere receives the greatest amount of solar energy around the 21st of December each year. However, the hottest days of the year are generally a month or so afterwards. Why do you think this is?