Sectieoverzicht
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Static electricity is usually caused by two objects rubbing together. and can be defined as: an imbalance of electric charges within or on the surface of a material or between materials. The charge remains until it can move away by means of an electric current or electrical discharge.
It works because everything is made of atoms.
Figure 1: Atoms are made of electrons which have a negative charge, protons which have a positive charge and neutrons which have a neutral charge. Usually there are an equal number of electrons and protons which gives an object a neutral charge.
Figure 2: In an atom the protons are attracted to the electrons and vice versa because opposites attract. Electrons will repel electrons and protons will repel protons because like charges will repel each other.
Usually there are an equal number of electrons and protons which gives an object a neutral charge. Static electricity is caused by an imbalance of those charges.
How do we know there are two types of electric charge? When various materials are rubbed together in controlled ways, certain combinations of materials always produce one type of charge on one material and the opposite type on the other. By convention, we call one type of charge “positive”, and the other type “negative.” For example, when glass is rubbed with silk, the glass becomes positively charged and the silk negatively charged. Since the glass and silk have opposite charges, they attract one another like clothes that have rubbed together in a dryer. Two glass rods rubbed with silk in this manner will repel one another, since each rod has positive charge on it. Similarly, two silk cloths so rubbed will repel, since both cloths have negative charge. Figure 2 shows how these simple materials can be used to explore the nature of the force between charges.
Figure 3: A glass rod becomes positively charged when rubbed with silk, while the silk becomes negatively charged. (a) The glass rod is attracted to the silk because their charges are opposite. (b) Two similarly charged glass rods repel. (c) Two similarly charged silk cloths repel.
Figure 4: As the child slides down the slide a static charge builds up in his hair which causes his hair to stand up.
You can try this: take a plastic ruler and rub it several times on someone's hair. Does it stick up?
The ruler will have an overall negative charge and the persons hair will have an overall positive charge. Each hair will repel other hairs because they have the same charge.
Figure 5: Styrofoam peanuts clinging to a cat's fur due to static electricity.
These charges can build up on the surface of an object until they find a way to be released or discharged. One way to discharge them is through a circuit.
When you jump on a trampoline or rub your socks on a carpet, you build up extra electrons and they will discharge when you touch something which will conduct electricity.
Important points to remember:
Whenever charge is created or destroyed, equal amounts of positive and negative are involved.
Both positive and negative charges exist in neutral objects and can be separated by rubbing one object with another. Negatively charged means an excess of electrons and positively charged means a depletion of electrons.
Methods of Charging
The following methods can charge a body by friction:
By rubbing two bodies together, both positive and negative charges in equal amounts appear simultaneously due to the transfer of electrons from one body to the other.
- A glass rod rubbed with silk makes the rod positively charged and silk negatively charged. The decrease in the mass of the glass rod is equal to the total mass of electrons lost by it.
- Ebonite (a type of plastic) on rubbing with wool becomes negatively charged, and the wool becomes positively charged.
- William Gilbert observed that when two glass rods, each rubbed against silk, are brought closer, they repel each other. Similarly, two ebonite rods rubbed against the cat’s skin repel each other. On the other hand, a glass rod rubbed against silk, and an ebonite rod rubbed against a cat’s skin on being brought closer attracts each other.
- Clouds also get charged by friction.
- A comb moving through dry hair gets electrically charged. It starts attracting small bits of paper.
- During landing or take-off, the tyres of an aircraft get electrified; therefore, special material is used to manufacture them.
- A truck carrying explosives has a metal chain touching the ground to conduct the charge produced by friction.
Activity 1
1. Click on the link below.
2. Move the balloon close to the sleeve of the jersey and observe what happens.
3. Now rub the balloon over the jersey. Can you see how the balloon 'collects' the negative charges?
4. Move the balloon over to the wall and observe what happens.
Because you rubbed the balloon on the surface of the jersey, it now has an overall negative charge. When you place the balloon on the wall, the negative charges in the wall are repelled, the negative charges in the balloon are attracted to the positive charges in the wall and the balloon will stick to the wall.
You can also try this: Take a blown-up balloon, rub it on a jersey or a cloth, and stick it on the wall.
Activity 2
1. Click on the link below:
https://phet.colorado.edu/sims/html/john-travoltage/latest/john-travoltage_en.html
2. Rub Johns leg on the rug. Do you see the electrons gathering on his body?
3. Place his finger near the metal doorknob. What happens?
The static electricity buildup discharges when the finger comes into contact with the metal doorknob.
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