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.
The amount of electricity flowing through a circuit can be measured on a device called an ammeter. It measures an electric current in amps short for amperes, A. An average household light globe uses about 0. An electric oven, however, may use over 5 A. Voltage is like the force that causes the electrons to flow through a circuit. However, a 1.
Most household lamps use V electricity. This voltage can supply a much larger force to make the current flow through the lamp. Household appliances such as stoves and television sets also use V. The power stations transfer electricity using even higher voltage, often several hundred thousand volts. The higher the voltage the more dangerous the electricity can be if it is not handled safely. The amount of current flowing through a circuit depends upon how easy it is for the electricity to flow.
If it is very easy, then a lot of electricity will flow. If it is very difficult, then much less electricity will flow.
The difficulty with which electricity flows through a circuit is called the resistance of the circuit. If it is very difficult for electricity to flow through a circuit, then the circuit is said to have a high resistance. A torch globe has a fairly high resistance. This is why electricity uses up energy in trying to pass through a globe.
If there are two light globes in a chain in series in a circuit, then the resistance is doubled. The electricity would have to use twice as much energy to get through.
Without that extra energy the two globes will be duller than if only one globe was in the circuit. To make the two globes in series work at full brightness, then two 1. Resistance is measured in units called ohms. The greater the resistance the greater the number of ohms. Some metals have more resistance than other wires. For example, tungsten metal has a greater resistance than copper wire. Silver has even less resistance than copper.
Non-metals such as plastic and rubber have extremely high resistances. This is why they are called insulators and are used as protection against electric shocks. The resistance of a wire is also affected by the size of the wire. A very thin wire has a higher resistance than a very fat wire. It is more difficult for the electrons to crowd through a narrow wire. A longer wire also has more resistance than a shorter wire.
It takes more electrical energy to make the electrons travel through a long wire than through a shorter length of the same wire. Electrical gadgets use electrical energy by converting it into other forms of energy. For example, a stove uses electrical energy by converting it into heat energy.
A light globe uses electrical energy by converting it into light energy and heat energy. An electric blender converts electrical energy into motion energy. Some household gadgets are more powerful than others. For example, an electric drill is more powerful than an electric shaver. An electric oven is more powerful than an electric light.
The atom also contains electrons. Where are the electrons arranged in the atom? The atom is held together by the electrostatic attraction between the positively charged nucleus and the negatively charged electrons.
Within an atom, the electrons closest to the nucleus are the most strongly held, whilst those further away experience a weaker attraction. Normally, atoms contain the same number of protons and electrons. This means that atoms are normally neutral because they have the same number of positive charges as negative charges, so the charges balance each other out. All objects are made up of atoms and since atoms are normally neutral, objects are also usually neutral. However, when we rub two surfaces together, like when you comb your hair or rub a balloon against your hair, the friction can cause electrons to be transferred from one object to another.
Remember, the protons are fixed in place in the nucleus and so they cannot be transferred between atoms, it is only electrons that are able to be transferred to another surface.
Some objects give up electrons more easily than other objects. Look at the following diagram which explains how this happens. When an object has more electrons than protons overall, then we say that the object is negatively charged. When an object has fewer electrons than protons overall, then we say that the object is positively charged.
So, we now understand the transfer of electrons that takes place as a result of friction between objects. But, how did that result in your hair rising when you brought the charged balloon close to your hair in the last activity?
Let's look at what happens when oppositely charged objects are brought together. This is a fun demonstration of how like charges repel each other and unlike charges attract each other. If you have enough materials, allow the learners to try this themselves. If you don't have enough materials, do this as a demonstration but give the learners a chance to play a bit. Practise this activity a few times first to make sure that you have the method right. Remember that it is quite easy to accidently earth the rods so work with care.
This will work best on a dry day. This will be dependent on the area which you live in. At a brainstorming workshop with volunteer teachers and academics at the beginning of , we filmed a quick demonstration of this task when the group was discussing it. You can view this short clip here:. The second perspex rod should repel the first one as they have like charges, so learners should see the second rod 'pushing' the first one around in a circle.
You might need to rub the first perspex rod again, in between attempts, as the charge does dissipate. The rods now have opposite charges and so the second rod should be seen to 'pull' the other rod around in a circle. When the rods are the same i. When the two different materials are used then the first rod should move towards the plastic rod and the watch glass will turn in a circle towards the plastic rod. When we rubbed the perspex rods with the cloth, electrons were transferred from the perspex to the cloth.
What charge do the perspex rods now have? Both the perspex rods now have the same charge. Did you notice that objects with the same charge tend to push each other away?
We say that they are repelling each other. When we rubbed the plastic rod with the cloth, electrons were transferred from the cloth to the plastic rod.
What charge does the plastic rod now have? The perspex rod and the plastic rod now have opposite charges. Did you notice that objects with different charge tend to pull each other together? We say that they are attracting each other. In the example of the pieces of paper being attracted to the ruler, the paper starts off neutral. However, as the negatively charged plastic rod is brought closer, the electrons in the paper that are nearest to the rod will begin to move away, leaving behind a positive charge on the surfaces of the paper that are nearest to the rod.
The paper is therefore attracted to the rod because opposite charges attract. Another example is dust that is attracted to newly polished glasses. Discover more with a simulation on rubbing balloons and a jersey. Do you now understand why your hair rises and is attracted to the balloon after you rub the balloon on your hair?
Write a short description to explain what is happening using the words: electrons, transfer, negative charge, positive charge, opposite, attract, repel.
When rubbing hair with the balloon, electrons are transferred from the hair to the balloon. The balloon now has a negative charge and the hair has a positive charge. They have opposite charges and so when the balloon is brought close to the hair again, they attract each other. Since the hair strands each have positive charges, like charges repel and the hair strands repel each other, also causing them to rise up.
Opposites attract and like repel video. A large build-up of charge on an object can be dangerous. When electrons transfer from a charged object to a neutral object we say that the charged object has discharged. Discharging can take place when the objects touch each other. But the electrons can also transfer from one object to another when they are brought close, but not touching.
When electrons move across an air gap they can heat the air enough to make it glow. The glow is called a spark. Sparks can be harmless, but they can also be very dangerous.
Sparks can cause flammable materials to ignite. You will probably have noticed that you may not smoke cigarettes or have open flames near petrol tanks at petrol stations. This is because petrol fumes are very explosive and only need a small amount of heat to start them burning. A small electrostatic spark is enough to ignite flammable petrol fumes.
A video showing the dangers of sparks of static electricity at a petrol station. This video in the Visit box shows how static electricity from the flowing petrol causes a spark which ignites the petrol fumes and leads to a large fire. It is an illustration of one of the dangers of static electricity. Electrostatic discharge can also cause electric shocks. Have you ever been shocked by a shopping trolley while you are pushing it around a shop?
Or have you walked across a carpeted room and then shocked yourself when you touch the door handle to leave the room? You have experienced an electric discharge. Electrons move from the door handle onto your skin and the movement of the electrons causes a small electric shock. Small electric shocks can be uncomfortable but mostly harmless. Large electric shocks are extremely dangerous and can cause injury and death. A simulation on friction between a carpet and John Travolta's foot.
The discharge of electrons from charged objects happens much more easily when the air is dry, which is why you are more likely to experience electrostatic sparks or shocks in dry weather.
This is because when the weather is humid, the moisture in the air can collect on the surface of objects, and prevent the build-up of electrical charge. The charge dissipates through the moisture, which is a better conductor than air. Do you know where else we can see sparks due to static electricity? Look at the photo for a clue! During a thunderstorm, there is friction in the atmosphere between the particles that make up clouds, causing the build-up of regions of charge.
Once the difference in charge between two regions becomes great enough, electrostatic discharge becomes possible. A lightning flash is a massive discharge between charged regions within clouds, or between clouds and the Earth. How to survive a lightning strike. In order to discharge extra electrons safely from an object we must earth it. Earthing means that we connect the charged object to the ground the Earth with an electrical conductor. The extra electrons travel along the conductor and enter the ground without causing any harm.
The Earth is so large that the extra charge does not have any overall effect. For example, think of the metal trolleys in shopping centres. Have you ever noticed that they normally have a metal chain hanging at the bottom which drags along the floor?
This is to earth the trolley if it gets a charge so that charge cannot build up on the trolley. This protects the person pushing the trolley from getting a shock. Rather, existing charges are moved about. In fact, in all situations the total amount of charge is always constant. This universally obeyed law of nature is called the law of conservation of charge.
Sometimes, the created mass is charged, such as when an electron is created. Whenever a charged particle is created, another having an opposite charge is always created along with it, so that the total charge created is zero. For example, an antielectron would usually be created at the same time as an electron.
The antielectron has a positive charge it is called a positron , and so the total charge created is zero. See Figure 7. All particles have antimatter counterparts with opposite signs. When matter and antimatter counterparts are brought together, they completely annihilate one another. Since the two particles have equal and opposite charge, the total charge is zero before and after the annihilation; thus, total charge is conserved. Figure 7. Here the matter created is an electron—antielectron pair.
The total charge before and after this event is zero. Only a limited number of physical quantities are universally conserved. Charge is one—energy, momentum, and angular momentum are others. Because they are conserved, these physical quantities are used to explain more phenomena and form more connections than other, less basic quantities.
We find that conserved quantities give us great insight into the rules followed by nature and hints to the organization of nature. Discoveries of conservation laws have led to further discoveries, such as the weak nuclear force and the quark substructure of protons and other particles.
The law of conservation of charge is absolute—it has never been observed to be violated. Charge, then, is a special physical quantity, joining a very short list of other quantities in nature that are always conserved. Other conserved quantities include energy, momentum, and angular momentum. Why does a balloon stick to your sweater? Rub a balloon on a sweater, then let go of the balloon and it flies over and sticks to the sweater.
View the charges in the sweater, balloons, and the wall. Skip to main content. Electric Charge and Electric Field. Search for:. Static Electricity and Charge: Conservation of Charge Learning Objectives By the end of this section, you will be able to: Define electric charge, and describe how the two types of charge interact. Describe three common situations that generate static electricity. State the law of conservation of charge.
Things Great and Small: The Submicroscopic Origin of Charge With the exception of exotic, short-lived particles, all charge in nature is carried by electrons and protons. Law of Conservation of Charge Total charge is constant in any process. Making Connections: Conservation Laws Only a limited number of physical quantities are universally conserved. Click to run the simulation. Conceptual Questions There are very large numbers of charged particles in most objects.
Why do most objects tend to contain nearly equal numbers of positive and negative charges? To start a car engine, the car battery moves 3. How many coulombs of charge were moved? A certain lightning bolt moves How many fundamental units of charge q e is this? Licenses and Attributions.
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