Explain principle and working of Hertz's experiment of accelerated charges with diagram.

Hertz’s experiment in context of electromagnetic waves is the experiment by Heinrich Hertz to detect existence of em waves. While Frank-Hertz accelerated electron experiment is a different experiment to prove the existence of quantized energy states in atom. The later being out of NCERT syllabus for class XII. The Hertz’s em wave detection is given below.  

Hertz’s experiment for the detecting electromagnetic waves predicted by J. C. Maxwell.

Principle: Charge accelerating in an electric field gives rise to em waves.

Construction: The experimental apparatus consisted of

  1. Induction coil
  2. Capacitor plate connected with spark knobs
  3. A metallic wire ring with spark knobs.


The induction coil converts the low voltage DC current to a high voltage AC current. This current lets the capacitor plates to be charged alternately and thereby generating electric sparks across the spark knobs.  As the spark jumps across the knobs em waves are generated.

Now when the ring is brought near the spark knob of the transmitter, the em waves generated induces opposite polarity across the spark gap of the ring and a spark jumps across it. This is the detection of the em wave generated by the transmitting circuit.

Conclusion: This experiment demonstrates the existence of em waves.  


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