Check out example codes for "how to change particle system rate over time unity". It will help you in understanding the concepts better.

Code Example 1

//objectName.GetComponent<ParticleSystem>().emission.rateOverTime = 2.0f;
//This doesn't work, so you need to seperate it into a few lines.
ParticleSystem particleSystem = objectName.GetComponent<ParticleSystem>();
var emission = particleSystem.emission;
emission.rateOverTime = 2.0f;

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