RADAR (Radio Detection and Ranging) is primarily used for which of the following purposes?

Introduction / Context:
RADAR is an important technology used in aviation, navigation, meteorology and defence. The name RADAR stands for Radio Detection and Ranging. It uses radio waves, not sound waves, to detect and determine the distance and direction of objects. This question asks you to identify the main application of radar among the given options.

Given Data / Assumptions:

• RADAR systems transmit pulses of radio waves.
• These waves can reflect off objects such as aircraft, ships or terrain.
• The system measures the time delay and direction of the returned signals.
• We are focusing on the primary and most common usage.

Concept / Approach:
Radar works by sending out radio waves and detecting their reflections from objects. By measuring the time taken for the echo to return and the direction from which it arrives, radar can determine the location, distance and sometimes speed of the object. This is widely used for tracking aeroplanes, ships, vehicles and even raindrops in weather radar. Locating submarines underwater is usually done with sonar, which uses sound waves in water, not radio waves. Ordinary radio receivers simply pick up broadcast signals; they do not perform detection and ranging like radar does.

Step-by-Step Solution:
Step 1: Recall the full form of RADAR: Radio Detection and Ranging. Step 2: Understand that radar transmits radio waves, which travel through air and space and reflect from objects. Step 3: The time delay between transmission and reception and the direction of the received signal allow the system to determine the position and distance of objects. Step 4: Aeroplanes, ships and other above-water objects are commonly tracked using radar systems. Step 5: Therefore, the correct main use is detecting and locating the position of objects such as aeroplanes.

Verification / Alternative check:
Air traffic control uses radar to monitor the positions of aircraft in controlled airspace. Marine radar helps ships avoid collisions, navigate in poor visibility and detect coastlines. Weather radars track rain and storm systems. All of these systems rely on radio waves and are termed radar. Submarines, in contrast, primarily use sonar (Sound Navigation and Ranging), which works with sound waves in water. Ordinary radio receivers or satellite tracking systems do not perform active detection and ranging in the same way as radar.

Why Other Options Are Wrong:
Locating submerged submarines deep under water: This is mainly done with sonar, not radar, because radio waves do not travel well in seawater.

Locating geostationary satellites in space using sound waves: Satellites are detected using radio and optical techniques, and sound does not travel through the vacuum of space; this description is incorrect on multiple counts.
Receiving ordinary radio broadcast signals in a radio receiver: A simple radio receiver only detects broadcast signals and does not emit its own radio waves to detect and range objects, so it is not radar.

Common Pitfalls:
Some students confuse radar with sonar because both involve waves and reflection. The key difference is that radar uses radio waves and is excellent in air and space, while sonar uses sound waves and is used underwater. Another confusion is to think that any use of radio technology must be radar; in reality, many systems use radio without performing detection and ranging.

Final Answer:
RADAR is used for detecting and locating the position of objects such as aeroplanes and ships.