An environmental monitoring satellite is in a stable circular orbit around the Earth, recording changes in global sea surface temperature.

Which statement is correct?

• The gravitational force on the satellite does work to maintain its circular path.
• The magnitude of the satellite's acceleration is constant but its direction is continuously changing.
• The satellite is moving with a constant velocity because its speed is uniform.
• The centripetal force is directed tangentially to the orbit.

All objects emit thermal radiation. The graph below shows how the spectral emissive power (intensity) of thermal radiation emitted by two solar thermal receiver plates, Plate X and Plate Y, varies with the wavelength of the radiation. Plate X is at a higher temperature than Plate Y.

Draw on this

Describe two differences between the graph for Plate X and the graph for Plate Y.

The global mean temperature of the Earth is maintained by a balance of incoming and outgoing radiation. Explain how the greenhouse effect acts as a thermal regulator for the Earth's surface, and why anthropogenic emissions of greenhouse gases are leading to a rise in global mean temperatures.

In your answer, you should discuss:

• the characteristics of the radiation absorbed and emitted by the Earth's surface.
• how atmospheric gases interact with this radiation to trap energy.