How do we know which plate has an excess of electrons?

It will be negatively charged.

negative charge will be present so show that this is an electrons

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A particle makes 240 revolution per min on a circular radius of 2m find its period

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To determine which plate has an excess of electrons, you can use a simple experiment involving a charged object. Here's how to set it up:

1. Take two identical metal plates, such as aluminum or copper, and connect them to a power source so that they become charged. One plate will be positively charged, and the other will be negatively charged. The power source can be a battery or a generator.

2. Use a charged object, such as a plastic rod rubbed with fur or a balloon rubbed on hair, to bring it close to one of the metal plates. The charged object will induce a temporary charge in the plate.

3. Observe the reaction of the metal plate as you bring the charged object closer. If the plate is attracted to the charged object, it means that the plate has a lower charge than the object. In this case, the plate is deficient in electrons and has an excess of positive charge.

4. Conversely, if the metal plate is repelled by the charged object, it means that the plate has a higher charge than the object. Thus, the plate has an excess of electrons and carries a negative charge.

By performing this experiment and observing the behavior of the metal plates in the presence of a charged object, you can determine which plate has an excess of electrons and is negatively charged.