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• Induced current in a circuit can be generated by electromagnetic induction, which occurs when a change in magnetic flux through a closed circuit induces an electromotive force (emf) that causes current to flow. This can be achieved by moving a magnet near a coil of wire or by changing the magnetic field strength through the coil.

(a) Four gases mainly present in biogas are methane (CH4), carbon dioxide (CO2), hydrogen (H2), and traces of hydrogen sulfide (H2S). (b) Advantages of using biogas over fossil fuels include:

1. Renewable: Biogas is produced from organic waste materials such as animal dung, crop residues, and kitchen waste, which are continuously generated and can be replenished naturally.
2. Environmentally Friendly: Biogas production reduces methane emissions from organic waste decomposition and displaces the use of fossil fuels, contributing to reduced greenhouse gas emissions and mitigating climate change.

• Biodegradable substances are those that can be broken down into simpler substances by the action of microorganisms such as bacteria and fungi, leading to their decomposition and recycling in the environment. Non-biodegradable substances are those that cannot be broken down by natural processes and persist in the environment for a long time, causing pollution and environmental damage.

Rainwater harvesting is the collection and storage of rainwater for future use. It can be done at the local level through the installation of rainwater harvesting systems such as rooftop rainwater harvesting, rainwater storage tanks, and permeable pavements. Benefits of rainwater harvesting include: