(a) Electromagnetic Waves for Radar Systems:
Radar systems used in aircraft navigation typically use microwaves. These waves are suitable because they can penetrate through clouds and other atmospheric obstacles, making them ideal for navigation and detection.
• Range of frequency: The frequency range for radar systems is typically between 1 GHz and 100 GHz, depending on the specific application. This range corresponds to wavelengths from 30 cm to 3 mm.
(b) Effect of Earth's Atmosphere on Surface Temperature:
If the Earth did not have an atmosphere, its average surface temperature would be lower than it is now.
• Explanation: The Earth's atmosphere plays a crucial role in regulating the planet's temperature through the greenhouse effect. The atmosphere traps heat from the Sun, preventing it from escaping back into space. Without an atmosphere, there would be no greenhouse effect, and the planet would lose heat more rapidly to space, resulting in a much colder average surface temperature. Estimates suggest the Earth's average temperature would be about -18°C (compared to the current average of around 15°C).
(c) Electromagnetic Wave Exerting Pressure:
An electromagnetic wave can exert pressure on a surface on which it is incident. This pressure is known as radiation pressure.
• Justification:
o When electromagnetic waves strike a surface, they transfer momentum to the surface. According to the principle of conservation of momentum, when the wave is absorbed or reflected by the surface, the surface experiences a force in the direction of wave propagation.
o The radiation pressure exerted by the wave is given by: P=IcP = \frac{I}{c} Where:
PP is the radiation pressure,
II is the intensity of the electromagnetic wave,
cc is the speed of light in a vacuum.
This pressure is extremely small but can be significant in certain contexts, such as with light sails or in the design of solar-powered spacecraft.
