Static charge
When insulating materials rub against each other, they may become electrically Electrical charge can be positive or negative. Like charges (+ and + or - and -) repel but unlike charges (+ and -) attract each other.. Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons., which are negatively charged, may be ârubbed offâ one material and on to the other. The material that gains electrons becomes negatively charged. The material that loses electrons is left with a positive charge.
Image caption, 1. A rod covered in negative charges is placed next to a duster covered in positive charges
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When a polythene rod is rubbed with a duster, the A force that opposes or prevents movement and converts kinetic energy into heat. causes electrons to gain energy. Electrons gain enough energy to leave the atom and ârub offâ onto the polythene rod.
- the polythene rod has gained electrons, giving it a negative charge
- the duster has lost electrons, giving it a positive charge
If the rod is swapped for a different material such as A type of transparent plastic film., electrons are rubbed off the acetate and onto the duster.
- the acetate rod has lost electrons, giving it a positive charge
- the duster has gained electrons, giving it a negative charge
Both of the rods and the duster are made of Material that does not allow charge or heat to pass through it easily. materials. Insulators prevent the electrons from moving and the charge remains A lack of movement. It means inactivity or stillness.. A material which allows charge to move easily through it., on the other hand, cannot hold the charge, as the electrons can move through them.
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Electrical forces
A charged object will experience a Force exerted between two objects, even when they are not touching, such as the force of gravity. from another charged object. The type of force will depend on the type of charge (positive or negative) on the two objects.
The properties of When two or more things come together, eg the north pole of a magnet is attracted to the south pole of a magnet. and When two or more things are forced apart, eg the north pole of a magnet is repelled by the north pole of another magnet. are often used to show that an object is charged:
- a charged rod can pick up small pieces of paper
- a charged balloon can stick to the wall by attraction
- a charged rod can pull a stream of water towards it
Example
If a negatively charged plastic rod is brought near to another negatively charged rod, they will move apart as they Objects that tend to push apart because of a force between them repel each other. each other.
If a positively charged rod is brought close to a negatively charged rod, they will pull together as they Objects that tend to move together because of a force between them attract each other. each other.
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The forces of attraction or repulsion are greater when the charged objects are closer.
Question
If a cloth rubs a plastic rod and the cloth is pulled away from the rod slightly, will the rod and cloth attract, repel or experience no force at all?
The rod and cloth will attract. This is true as long as there is enough friction to transfer electrons.
- if electrons are rubbed off the cloth and onto the rod - the cloth will be positively charged and the rod will be negatively charged
- if electrons are rubbed off the rod and onto the cloth - the cloth will be negatively charged and the rod will be positively charged
In both cases, the opposite charges will attract.
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