Question

why why is there a key in electric current? And answer

Answer 1

The key is attached in electric circuit to regulate the flow of electrons through the circuit.
i.e. when the key is open there is no electricity flowing through the circuit.

Answer 2

Answer:

Solar energy is radiant light and heat from the Sun that is harnessed using a range of ever-evolving technologies such as solar heating, photovoltaics, solar thermal energy, solar architecture, molten salt power plants and artificial photosynthesis.