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Context:  

Traffic police have started using speed guns to crack down on speeding vehicles all over India lately.

What is a Speed Gun?

It is a device for measuring the speed of a moving object without having to be in contact with the object. To achieve this, the device reflects electromagnetic radiation of a certain frequency from an object, captures the reflection, and uses the Doppler effect to infer the speed of the object.

Speed ​​guns are electronic and use complex circuitry to emit the radiation used for measurement. The speed gun was originally developed during World War 2 for military use and applies the effect using radio waves rather than sound waves.

How does it work?

• The speed gun has a radio transmitter and receiver.
• The transmitter emits radio waves that the person holding the speed gun can point at an object. The receiver collects the waves reflected from the object back in the direction of the speed gun.
• If the object is approaching the speed gun, the frequency of the returning waves will be slightly higher than the frequency of the transmitted waves. A simple computer in the weapon can derive the velocity of the object based on this difference.

How are speed and effect related?

• All electromagnetic waves have a fixed speed — equal to the speed of light in that medium.
• In a vacuum, this value is denoted by c: 299,792,458 m/s. Any change in frequency that the speed gun detects directly corresponds to the Doppler shift caused by the motion of the object.
• This principle is effective because it allows the speed gun to operate accurately over a wide range of distances and speeds without being affected by air resistance.
• A speed gun can calculate the speed of a moving object by multiplying the difference (between the received and emitted frequencies) by c and dividing by the emitted frequency times 2.
• This relationship shows how the difference is directly proportional to the speed of the object: the faster it moves, the more pronounced the difference will be.

Applications:

It is widely used by law enforcement officials to monitor traffic speed, coaches to measure the performance of their athletes, and various other industries that need accurate movement tracking.

Doppler effect: It is the change in wave frequency due to relative motion between source and observer.

Disadvantages of Speed ​​Guns

• Beam divergence: Radio waves propagate and potentially measure multiple objects simultaneously.
• Problems with continuous radars: Susceptible to interference from multiple vehicles.
• Technological limitations: Requires advanced compensation systems for accurate targeting, which increases cost.
• Replacement for LIDAR: Laser speed guns provide better accuracy and targeting and overcome the divergence limitations of radio waves.

Source:

THE HINDU