Two different materials, rubbed against each other acquired opposite charges when separated. This is an example of charging by

Step 1: Analyze the question Two different materials are rubbed against each other. When they are separated, they carry opposite charges. We need to name the method of charging.

Step 2: Explain the concept There are three main ways to charge an object:

• Friction (rubbing): Two different insulating materials are rubbed together. Electrons transfer from one material to the other. The one that loses electrons becomes positive, and the one that gains them becomes negative. Examples: a glass rod rubbed with silk (the glass becomes positive, the silk negative), or ebonite rubbed with fur (the ebonite becomes negative).
• Conduction: A charged body touches a neutral conductor, and charge flows between them. Both end up with the same type of charge.
• Induction: A charged body is brought near (without touching) a neutral conductor, which causes charge separation. The conductor is then earthed and ends up with the opposite charge to the inducing body.
• Convection is a method of heat transfer in fluids, not a method of charging.

Step 3: Apply to the question

• The materials were rubbed together, which is the key word pointing to friction.
• Both bodies end up with opposite but equal charges because electrons move from one to the other.
• Induction needs no contact and an earthing step, and conduction needs a charged body touching a neutral one. Neither describes this situation.
• Convection has nothing to do with charging.

Step 4: Answer The correct option is B. friction.

Tip: Look for the keyword in the question. "Rubbed" means friction, "touching" means conduction, and "bringing near without touching" means induction. Also remember that charging by friction always produces opposite and equal charges on the two materials.