State the basic radar range equation used in air traffic radar.

• A. R = c × t
• B. R = t / (2c)
• C. R = (c × t) / 2
• D. R = 2c × t

Answer: (C)

The basic idea is that radar range comes from how long the pulse takes to travel to a target and back. The pulse moves at the speed of light, c, so the round-trip distance covered in time t is c × t. Since that distance is twice the one-way range (out to the target and back), 2R = c × t. Solve for R to get R = (c × t) / 2. In air traffic radar, you use the speed of light in air (very close to c) and the measured two-way time to compute range. For example, t = 2 microseconds gives R ≈ (3×10^8 m/s × 2×10^-6 s)/2 = 300 meters. The other expressions don’t fit that geometry: they either ignore the round trip or place the factor of 2 incorrectly, leading to the wrong range.