Resistors

Resistors control current in electric circuits to prevent damage from high current by converting electrical energy into heat. Appliances like ovens and kettles act as specialized resistors.

Food Preservation

Food processing makes food safer, improves quality, and extends freshness. Methods include cooking, freezing, pickling, drying, and pasteurization, but can result in nutrient loss and higher prices. Food spoils due to microorganisms like bacteria and mold.

Grain Conservation

Grains are staple foods stored in silos or at home, dried to prevent rotting, and protected from pests. Storage methods include clay pots, grass baskets, grain wells, bags, and grain huts.

Methods of Preserving Food

1. Pickling: Food in brine prevents microbial growth. Common South African pickles include Achaar and chutney.

2. Curing and Drying: Curing with salt preserves food by preventing spoilage. Examples are Biltong and Dipabi.

Metal Preservation Methods

• Painting: Protects metals from rust and improves appearance.

• Galvanizing: Coating iron/steel with zinc prevents rust.

• Electroplating: Applies a protective coating of one metal over another for corrosion resistance.

Plastic

Plastics are versatile but cause environmental pollution. They are divided into thermoplastics (recyclable) and thermosetting plastics (not recyclable). Reducing, reusing, and recycling are key measures to combat plastic waste.