S1 - Bright Sparks Summary Notes

Electricity – Van de Graaff Generator and Circuit Symbols

1–We are investigating the purpose of a Van de Graaff Generator. 2–We are considering circuit symbols for various components.

All objects in the universe, living and non-living are made up of atoms. All atoms consist of a small nucleus in the centre that contains protons and neutrons.

Protons have an electrically positive charge whilst neutrons are neutral (i.e. they have no electrical charge) Orbiting the nucleus are small fundamental particles called electrons which have an electrically negative charge. Protons and neutrons are firmly fixed in the nucleus but electrons can be free to move. This is what electricity is all about – the movement of electrons.

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How it works: As the rubber belt turns, it rubs against a piece of metal connected to the dome. Electrons from the atoms that make up the rubber belt are released and build up on the dome. If you are touching the dome the electrons will move onto you. Electrons are negatively charged so they repel each other. This means that all the electrons in your hair are trying to move away from each other and as your hair is very light it stands up. If you touch someone whilst on the Van de Graaff generator the electrons on you can jump to the other person. You both feel a shock and you may see a small spark. This flow of electrons is called an electrical current. The insulation under you and the Van de Graaff generator is there to stop the electrons escaping.

Circuit Symbols

Switch

Lamp

Wire/Lead

Buzzer

Battery

Remember that we use circuit symbols because they are much easier and quicker to draw than pictures (like those in the right hand column of the table above).

Electricity – Current in a series circuit

3 – We are learning to investigate the flow of current at different points in a series circuit.

A series circuit is where all the components are connected one after the other “in line”. The circuit below shows two lamps in series with each other.

The size of the current can be measured using a meter called an ammeter. A The unit of electrical current is an ampere (A). Ammeters must be placed in series with other components in a circuit as shown below.

Example:-

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A1

A2

A3

1.5 V 1.5 V

The current in a series circuit is

the same at all points.

i.e. in the circuit shown A1, A2

and A3 are all equal.

In the circuit opposite we can see

that the ammeter readings of I1

and I2 are equal to the supply

current Is.

i.e. Is = I1 = I2

3A = 3A = 3A

Electricity – Voltage in a series circuit

4 – We are learning to investigate what happens to the voltage in a series circuit.

The electrical push which the battery gives to the charges is called the voltage. The voltage is measured in volts on a voltmeter V Voltmeters are connected across the part of the circuit where the voltage has to be measured. i.e. they are connected in parallel into the circuit as shown below.

In a series circuit the total voltage measured across its components adds up to the supply voltage. i.e. In the circuit below V3 = V1 + V2

Example:-

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V3

V2 V1

In the circuit opposite we can see

that the voltmeter readings of

V1, V2 and V3 add up to the

supply voltage Vs.

i.e. Vs = V1 + V2 + V3

= 4 + 4 + 4

= 12V

Electricity – Current in a parallel circuit

5 – We are learning to investigate the flow of current at different points in a parallel circuit.

A parallel circuit is where components are connected across each other. In the circuit below two lamps are connected in parallel.

For the parallel circuit below, the current in A1 and A4 will both be the same value. The currents in A2 and A3 add up to equal both A1 and A4.

Example:-

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In the circuit opposite we can see

that the ammeter readings of I1,

I2 and I3 add up to the supply

current Is.

i.e. Is = I1 + I2 + I3

= 6 + 6 + 6

= 18A

Electricity – Voltage in a parallel circuit

6 – We are learning to investigate what happens to the voltage in a parallel circuit.

Example:-

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In a parallel circuit the voltage

measured by the voltmeters

across each branch of the circuit

will be exactly the same and

equal to the supply voltage.

i.e. V1 = V2 = V3

In this circuit we can see that the

voltage across each lamp in

parallel is the same and equal to

the supply voltage from the

battery.

i.e. Vs = V1 = V2 = V3

12V = 12V = 12V = 12V

Hot Stuff – Heat transfer in solids

6 – We are learning to investigate how heat is transferred in solids in terms of particle motion.

Solid The particles are tightly packed together and vibrate in their own position. They have the same volume and the same shape. Liquid The particles are tightly packed together but slide over each other, changing position. They have the same volume and take up the shape of the container. Gas The particles are spaced far apart and move about fast taking up the shape of the container.

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Conduction in Solids In the experiment below the rivets fall off one by one in order 1, 2 then 3. This shows that heat energy is travelling along the metal rod from the flame. This form of heat transfer is called conduction.

The diagram below shows how the particles of the metal rod close to the flame gain energy and start to vibrate more vigorously. These particles then collide with neighbouring particles which in turn start to vibrate more. This process continues along the length of the metal rod.

Conduction in non-metal solids In the experiment below the heat sensitive paper on the metal rod changes colour but the paper on the non-metal rod does not. This shows that heat energy travels along the metal rod from the flame but not through the non-metal rod.

We are able to conclude that metals are good conductors of heat but non-metals are poor conductors of heat. Conduction in Gases In the experiment below the match on the metal rod sets alight but the match in the air does not. This shows that heat energy travels along the metal rod to match An but not through the air to match B. We are able to conclude that gases are poor conductors of heat.

Conduction in Liquids In the experiment below the water at the top of the test tube is boiling yet there is still a lump of ice in the wire gauze and the water around it remains very cold. This shows that heat energy has not travelled from the water at the top of the test tube to the water at the bottom. We are able to conclude that liquids are poor conductors of heat.

Hot Stuff – Heat transfer in Liquids and Gases

7 – We are learning to investigate how heat is transferred in liquids and gases.

The previous experiments concluded that liquids and gases do not conduct heat very well, yet heat clearly travels through liquids and gases. Otherwise how could we have hot baths and how would hot air balloons work. Heat transfer in liquids and gases occurs through the method of convection. This is where hot liquids or gases become less dense and rise whereas cold liquids and gases become more dense and sink. This is called a Convection Current. When gases or liquids are heated, the particles have more energy so move further away from each other. This makes the gas or liquid less dense than the air or liquid around it. As it is less dense it is also lighter than the surrounding air or liquid which means it rises.

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Hot Stuff – Heat transfer in a Vacuum

8 – We are learning to investigate how heat is transferred in a vacuum.

In both conduction and convection, heat transfer involves particles. Space is a vacuum (i.e. there are no particles) so the heat we get from the sun cannot be transferred by either of these methods. Instead heat travels from the Sun to us by a process called Radiation.

All objects give out and take in thermal radiation, which is also called infrared radiation. The hotter an object is, the more infrared radiation it emits.

Infrared radiation is a type of electromagnetic radiation that involves waves. No particles are involved, unlike in the process of conduction and convection. This is why we can still feel the heat of the Sun, although it is 150 million km away from the Earth.

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Hot Stuff – Heat Loss

9 – We are investigating how heat is lost from our homes and how we can reduce it.

Heat loss in the home We have already identified that heat can be transferred by the methods of conduction, convection and radiation. Each of these methods can be useful for various aspects of our lives but it can also have a negative effect. An example of this is heat loss in our homes where heat can be lost in many different ways, resulting in cold homes or huge energy bills. The diagram below shows where most heat is lost in a typical home. In order to reduce our energy bills and keep our homes warm we can take steps to prevent or reduce some of these heat losses. Here are some common examples:

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