Why does a ruler become negatively charged

A plastic comb and your hair are both electrostatically neutral. This means that they have about the same number of negative and positive charges in them. What are the charges? Well, all the objects that you see around you are really just made of different combinations of three things: negatively charged electrons, positively charged protons and neutral neutrons.

The charge on the electron is the same magnitude as the charge on a proton except opposite signs. So, an object with the same number of electrons and protons will have a zero net charge.

When you rub the plastic in your hair, there is an interaction between the molecules in the comb and the molecules in your hair. During this interaction, some of the charges from one of the objects get transferred to the other. One object becomes positively charged and one becomes negatively charged. If you are really curious, you can look up the two materials in the triboelectric series.

From this, plastic rubbed in hair would make the plastic negatively charged and the hair positively charged. But why does this negatively charged plastic attract neutral paper? The answer is that the paper becomes electrically polarized. Eg: if you rub a pyrex glass rod against wool, wool will lose electrons to the glass rod. Thus making the wool positively charged and the glass rod negatively charged.

Why does a plastic ruler rubbed on hair loses electrons and gets a positive charge? Please explain briefly. Thank you. Jun 8, When the negatively-charged rod is brought close to the electroscope, positive charges are attracted to it and negative charges are repelled away from it. If they are brought into contact, they will both take a net negative charge. Skip to content Technology. May 8, Joe Ford. Table of Contents. Similarly if a positively charged rod is brought near to another positively charged rod, they gently repel each other.

The above effects can be summarised in a law: Opposite charges attract. Like charges repel. When you feel an electric shock as you get off a trampoline or after your have been walking across a new clean dry carpet, you are feeling billions of electrons passing through your body. If you get an electric shock from a power cord, you may have even more electrons passing through your body.

The electricity that flows through a power cord is just a flow of negatively charged electrons. The speed at which they flow is very, very slow, but there are so many billions of them that they can still have a huge effect. Copper atoms, like most other metals atoms, have very loosely held outer electrons.

They are so loose that they seem to make a sea of electrons. They can easily move around copper atoms inside the wire. The flow of electric charge, such as the motion of these loosely held electons in a copper wire, is called an electric current.

If a length of copper wire is connected between the top of a battery and the bottom of the battery, the outer electrons in the wire can be made to flow from one end of the wire to the other.

The crowd of negative electrons produced at the base of the battery repel the loose electrons in the copper wire connected to this end of the battery, because they all have the same electric charge. The positive charge at the top of the battery tends to attract the loose electrons in the copper wire, because they have opposite charges.

However, no electrons in the copper wire can move through the wire unless they all move. This can only happen when both ends of the wire are in contact with the terminals of the battery simultaneously. Only then an electric current can flow through the wire. If the wire is broken in the middle, all the electrons must stop and no electric current can flow.

A continuous, uninterrupted path through which charges can move is called an electric circuit. There are two main types of electrical circuits. They are called series and parallel. When several light globes are connected in a 'chain' they are said to be connected in series.

In a series circuit the same number of electrons must be flowing through each lamp in turn. If a million electrons each second are flowing through the first lamp, then there must be a million electrons flowing through the other lamps each second. A series circuit has some limitations. If you turn off one of the lamps in series, all the other lamps will be turned off.

This is because if you stop the current flowing through one lamp, the current flowing through all the lamps must stop. Also if one lamp in the series circuit 'blows' ie stops working all the other lamps will stop working since the blown globe will halt the flow of electricity in the circuit.

Series circuits have been used in some Christmas tree decorations where long chains of lights are needed. However, series circuits are not suitable for most uses in houses. Image how it would be if to turn on one light, you had to turn on all the lights and if one light stopped working, they would all stop.

When several lamps are connected like the steps on a ladder they are said to be connected in parallel. In a parallel circuit the flow of electrons coming out of the battery divides up so some of the electrons flow through each lamp. If the electrons are prevented from flowing through one of the lamps, they can still flow through the other lamps. Each lamp can be turned on and off independently. Parallel circuits are the most useful circuits used in houses. The use of parallel circuits means that lights and appliances can be turned on and off independently in each room.