Electric Forces and Static Charge

Electrostatic Charging

• Glass rod rubbed with silk cloth: Acquires a positive charge.
• Two identical polythene rods: Repel each other because they acquire the same charge (negative).
• Negatively charged polythene rod near uncharged rod: Attracts the uncharged rod due to charge separation.
• Conductor: Material allowing free movement of electric charge, like metals.
• Defining characteristic of a conductor: The presence of free electrons which can move easily.
• Oppositely charged rods: Attract each other.
• Polythene rod rubbed with woolen cloth: Acquires a negative charge.
• Two objects have the same charge: They repel each other.
• Two charges of the same type brought closer: Electric force between them increases.
• Interaction between opposite charges: They attract each other.
• Static charge buildup: Caused by friction, transferring electrons between materials.
• Good heat conductors: Materials with free electrons like metals.
• Rubbing a plastic comb through hair: Comb gains a negative charge, hair becomes positively charged.
• Increasing distance between charged objects: Electric force decreases.
• Negative particle in electric field (positive charge): Experiences a force in the opposite direction of the field.
• Relationship between electric force and field strength: Electric force is proportional to the strength of the electric field.
• Electric field lines around a positively charged sphere: Radiate outwards from the sphere.

Materials and Charge

• Charging by friction: Transfer of electrons between materials, creating static charge.
• Shape of electric field lines in a uniform field: Parallel straight lines.
• Plastic rod rubbed with cloth: Rod gains a static charge, either positive or negative, depending on the material of the cloth.
• Electric field pattern between two charged spheres: Resembles lines joining the spheres.
• Insulating materials rubbed together: Electrons transfer from one material to another, creating static charges.

Static Electricity

• Example of static electricity: Lightning, sparks when touching metal objects, shocks from clothes.
• Behavior of charges on insulators after friction: Charges remain localized on the surface of the insulator.
• Object receiving electrons: Acquires a negative charge.
• Object losing electrons: Acquires a positive charge.
• Static electricity in terms of charge interaction: It involves the buildup and discharge of static charges.
• Charging by induction: Process of redistributing charges within an object by bringing a charged object nearby.
• Dangerous static electricity: Can happen during refuelling of aircraft due to friction, leading to explosions.
• Application of static electricity: Photocopiers, electrostatic precipitators for air purification.
• Material likely to give up electrons: Materials that are easily oxidized, like wool.

Conductors and Insulators

• Rubbing a plastic rod with cloth: The plastic rod and cloth achieve opposite charges.
• Better conductor of electricity: Metals, due to free electrons.
• Characteristic of metals for good conduction: The presence of delocalized electrons that can move freely.
• Insulator: Material that resists the flow of charge due to tightly bound electrons.
• Electric field lines in an electric field: Represent the direction of force on a positive test charge placed in the field.
• Strength of electric field: Is proportional to the number of field lines per unit area.
• Better insulator: Materials like rubber, glass, and plastic.
• Factors not affecting charge flow in a conductor: The shape of the conductor.
• Electrons in a conductor: Are delocalized and move freely throughout the material.