Physics Unit 14.2+3: A.C. Generator, Transformer

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Unit 14.2: A.C. Generator

1. Describe a rotating-coil generator and the use of slip rings

A little terminology to learn first:
A.C. = alternating current. This means instead of the current flowing in one direction, it flows back and forth.

Here's an example of an A.C. generator

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Between the magnet is a magnetic field. The wire loop is made of insulated copper wire and is turned. As it turns, it cuts those magnetic field lines, inducing current and generating electricity that can power a bulb if it is attached to the generator. 

The slip-rings are connected to the coil of wire, while the carbon brushes are connected to an external circuit. The brushes are constantly in contact with the slip-rings so that the current can flow from the coil to the external circuit. 

You can see that the magnetic field lines run horizontally. If the coil is also laid horizontally, it lays in line with the field lines and don't cut them, so no current is induced. When the coil is rotated, it begins to cut the field lines at angles. At 45 degrees, a small current produced; at 90 degrees, a larger current is produced. 

2. Sketch a graph of voltage output against time for a simple a.c. generator.

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This diagram further elaborates on the 45° and 90° explanation from above.

Unit 14.3: The Magnetic Effects of a Current

1. Describe the construction of a basic iron-cored transformer as used for voltage transformations.

A transformer is an electrical device that changes the voltage of an A.C. current supply. For some devices, only a small voltage is needed to charge it. A transformer helps decrease the high voltage from the electrical source so when charged, the device will not break. This transformer is called a step-down transformer as it is stepping down the voltage. This can be reversed and we will have a step-up transformer.

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An electric current is passed through the primary coil of wire. The magnetic field from the primary wire grows, collapses, turns (because it's an a.c. current), grows, collapses; those field lines cut the secondary wires, inducing electricity. The diagram above shows a step-down transformer as the secondary wire has less coils. Therefore, the output voltage will be smaller. The more coils present, the stronger the current will be. 

2. Recall and use the equation (VP / VS) = (NP / NS). 

V stands for the voltage while N stands for the number of turns. The voltage and number of turns are proportional, so the factor affecting one side of the equation will also affect the other. Below is an example:

3. Describe the use of the transformer in high-voltage transmission of electricity.

The National Grid is the nation's power supply. It transfers electricity from the Grid to homes for use. When a current is passed through those the wires of the Grid, heat is lost. Since it needs to supply electricity for many different places, a high current is needed; however this results in a lot of energy being lost as thermal energy. Instead, the Grid transmits electricity at a low current to reduce heat loss. A high voltage is required in order for this to work. Since a high voltage is dangerous to use in homes, transformers are used to step down this power supply, making it safe to use.

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4. Recall and use the equation Vp / Ip = Vs / Is (for 100% efficiency).

We know that voltage divided by current gives power, so this equation tells us the primary power is the same as the secondary power. With this equation you can determine how much power goes through one end of the transformer and how much goes out, since it is assumed that the transformer is 100% efficient and does not waste any energy.

5. Explain why energy losses in cables are lower when the voltage is high. 

As said above, energy is lost as heat when a current is run through a wire. From the power equation we know that voltage and current are proportional to make the final power product. If the voltage is high, this means the current is low, resulting in less power loss. 

Physics Unit 3.2: Energy Resources

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Unit 3.2: Energy Resources

1. Distinguish between renewable and non-renewable sources of energy.

Renewable sources of energy are sources of energy that can replenish itself, will not run out, and does not harm the environment. Examples are solar energy and wind energy. Non-renewable sources of energy are sources of energy that are used up once used, and cannot be replaced. Examples include coal and oil.

2. Demonstrate understanding that energy is released by nuclear fusion in the Sun.

Because of nuclear fusion reactions within the Sun, it radiates energy. A small fraction of this energy reaches the Earth.

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3. Know that the Sun is the source of energy for all our energy resources except geothermal and nuclear. 

The Sun's energy can be used for solar panels and cells. It also in the food we eat, wood that we burn, biofuels from waste, plants, and fossil fuels. The Sun's energy has helped shape the end product that we come in contact with. 

Geothermal energy is due to the heat from the deep, hot layers within the Earth. Nuclear energy comes from a process called fission, which is the process of splitting uranium atoms. The energy released form fission produces steam that can turn a turbine, similar to how the steam from heating water with fossil fuels can turn a turbine.

4. Describe how electricity or other useful forms of energy may be obtained from; 

● chemical energy stored in fuel,

● water, including the energy stored in waves, in tides, and in water behind hydroelectric dams,

● geothermal resources,

● nuclear fission,

● heat and light from the Sun (solar cells and panels)

● wind.

Chemical energy can be obtained from burning fuel. When the fuel (oil, coal, wood, waste biofuels) is burnt, it releases heat energy, resulting in an exothermic reaction.

We can also obtain energy from the movement of water. Water is moved by wind, tidal energy, or being held back in a dam and then released; the movement turns generators in the water that create energy.

As mentioned above, geothermal energy comes from hot rocks deep underground. The thermal energy released heats water, which creates steam that can drive generators or heat buildings. Nuclear energy is a reaction due to fission, and this also heats up water to create steam.

Solar cells and panels suck up heat energy directly from the Sun, as they must be in contact with the Sun in order to work.

Wind energy is using the wind's movement to push turbines and turn generators.


5. Give advantages and disadvantages of each method in terms of reliability, scale, and environmental impact.

Energy source	Advantages	Disadvantages
Fuel	- ready-made - cheap	- unenvironmentally friendly - creates greenhouse gases
Wave	- renewable - does not produce greenhouse gases	- source may not always be present
Tidal	- renewable - does not produce greenhouse gases	- source may not always be present
Hydroelectic	- renewable - does not produce greenhouse gases	- hydroelectric plants affect life in the water - expensive to develop usage sites
Geothermal	- renewable - does not produce greenhouse gases	- effectiveness varies on the location - expensive to develop usage sites
Nuclear	- a small amount of radioactive material produces lots of energy - relatively cheap - no atmosphere pollutants	- creates nuclear waste - leakage of nuclear waste is very serious
Heat	- renewable - does not produce greenhouse gases	- source may not always be present - expensive to make solar panels
Light	- renewable - does not produce greenhouse gases	- source may not always be present
Wind	- renewable - does not produce greenhouse gases	- a lot of land is needed to build wind turbines - noisy - visual pollutant - energy can't be produced in large quantities - source may not always be present

6. Recall and use the equation: efficiency = energy input/useful energy output x 100%

Efficiency = energy input/useful energy output x 100%

7. Demonstrate a qualitative understanding of efficiency. 

For example, if 100J of energy goes into a lamp and 75J of light energy comes out, the efficiency of the lamp is 75%.

Physics Unit 11: Magnetism

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Unit 11: Magnetism

1. Describe the properties of magnets.

● opposite poles attract; same poles repel

● field lines travel from N to S

● produces a magnetic field which can then produce a current

● a temporary magnet that loses its magnetism easily is known as a soft magnet

● a permanent magnet that does not lose its magnetism easily is known as a hard magnet

2. Give an account of induced magnetism.

When you rub a wire between a N and S pole, the wire cuts the horizontal magnetic fields at a 90° angle. This induces a current. 

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The same thing occurs with a solenoid (a coil of wire) and a magnet. The magnet is moved inside the solenoid, creating a current. 

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The speed of the magnet within the solenoid and the amount of coils of the solenoid both affect the current induced. Faster movement and more coils induce a greater current. 

3. Identify the pattern of field lines round a bar magnet.

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This diagram basically sums up this point on the syllabus. 

4. Distinguish between the magnetic properties of iron and steel.

Iron	Steel
Is a soft magnet	Is a hard magnet
Useful for making temporary electromagnets; strong but temporary	Slow to magnetise but retains its magnetism
High susceptibility, low retentivity	Low susceptibility, high retentivity

5. Distinguish between the design and use of permanent magnets and electromagnets.

Permanent magnets

● magnetism is permanent

● its atoms are aligned to produce a constant magnetic field

● used for compasses, fridge magnets, and cabinet doors

Electromagnets

● magnetism works only when a current is induced

● used for transformers, motors, and loudspeakers

Chemistry Unit 12: Sulphur

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Unit 12: Sulphur

1. Describe the manufacture of sulphuric acid by the Contact process, including essential conditions.

The manufacture of sulphuric acid is called the Contact Process and this is the process: firstly, you need to burn sulphur in oxygen to create sulphur dioxide. The sulphur dioxide is then passed over a vanadium pentoxide catalyst to form sulphur trioxide. Essential conditions for maximum yield of sulphur trioxide is 450°c and a moderate amount of atmospheric pressure. The sulphuric trioxide is then dissolved in water to produce sulphuric acid. 

Here's how it goes with symbol equations:

1. sulphur + oxygen --> sulphur dioxide

S + O2 --> SO2

2. sulphur dioxide + oxygen --> sulphur trioxide (vanadium pentoxide catalyst, 450°c, atmospheric pressure)

SO2 + O2 --> SO3

3. sulphur trioxide + water --> sulphuric acid

SO3 + H2O --> H2SO4

2. Describe the properties of dilute sulphuric acid as a typical acid.

● eats away and dissolve objects

● readily absorbs moisture

● corrosive

● reacts with bases

● doesn't conduct electricity

Biology Unit 9.3: Monohybrid Inheritance

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Unit 9.3: Monohybrid Inheritance

1. Define the terms genotype, phenotype, homozygous, heterozygous, dominant, and recessive.

Genotype: the genetic makeup of an organism in terms of the alleles present.

Phenotype: the physical or other features of an organism due to both its genotypes and its environment.

Homozygous: having two identical alleles of a particular gene (e.g. TT or gg). Two identical homozygous individuals that breed together will be pure-breeding.

Heterozygous: having two different alleles of a particular gene (e.g. Tt or Gg); not pure breeding.

Dominant: an allele that is expressed if it is present (e.g. T or G)

Recessive: an allele that is only expressed when there is no dominant allele of the gene present (e.g. t or g).

Alleles are different forms of the same gene. For example, a certain gene controls eye colour but there are many eye colours out there. If you inherit two different alleles for a particular gene, one may be stronger than the other; the stronger one is the dominant allele while the weaker one is the recessive allele. The effect of the recessive will be masked by the dominant. Dominants are represented with capital letters (e.g. B for a dominant brown allele controlling eye colour) and recessives with lower case letters.

Following on with the eye colour situation: you've got a mother with brown eyes (Bb genotype (B for the dominant brown allele, b for the recessive blue allele)) and a dad with blue eyes (bb genotype). Like with multiplication, you can use a punnet square to calculate outcomes.

	b	b
B	Bb	Bb
b	bb	bb

Let's use the eye colour problem again to describe heterozygotes and homozygotes. If an individual ended up with an Bb genotype, they are known to be heterozygotes because they have two different alleles that make up their eye colour. The individual with the bb genotype is known to be a homozygote because they have the same kind of allele that makes up their eye colour.


2. Calculate and predict the results of monohybrid crosses involving 1:1 and 3:1 ratios.

To understand this concept let's use an example involving flowers, because flowers are nice. We can take two red flowers and predict their breeding outcomes. One flower's genotype is RR, while the other is Rw; the latter flower contains a recessive white allele.

	R	R
R	RR	RR
w	Rw	Rw

The ratio of a heterozygous flower to a homozygous flower is 1:1. 

Say you take two purple flowers and and want to breed them to produce a flower. The genotype of the purple flowers would be Pw, where the dominant allele is purple and the recessive allele is white.

	P	w
P	PP	Pw
w	Pw	ww

From the punnet table we see that the possibility of producing a purple flower is 3/4, while producing a white flower is 1/4. The ratio is 3 purples : 1 white.

Biology Unit 9.1+2: Chromosomes and Genes, Cell Division

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9.1: Chromosomes and Genes

1. Define inheritance as the transmission of genetic information from generation to generation.

Well, there you go! But here's a little more detail: inheritance is how parents pass on their characteristics to their children or offspring.

2. Define the terms chromosome, gene, and allele.

Chromosome: A thread of DNA, made up of a string of genes.

Gene: A length of DNA that is the unit of heredity and codes for a specific protein. A gene may be copied and passed on to the next generation. 

Allele: Any of two or more alternative forms of a gene.

3. Define the terms haploid nucleus and diploid nucleus.

Haploid nucleus: a nucleus containing a single set of unpaired chromosomes.

Diploid nucleus: A nucleus containing two sets of chromosomes.

A set is 23 single chromosomes, meaning a haploid nucleus has 23 chromosomes while a diploid nucleus has 46 (who pairs of 23). Body cells (somatic cells) are known as diploid nucleuses, while male and female gametes are haploid nucleuses. 

When an egg and sperm fuse in the process of fertilisation, the 23 chromosomes from the egg and the 23 chromosomes from the sperm add up together in the zygote, returning the chromosome number to 46. (Each gamete is a h______ n______; the zygote is a d______ n______)

Think about it this way:
Haploid sounds like half;
Diploid means 'double' or 'two'

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4. Describe the inheritance of sex in humans (XX and XY chromosomes)

All eggs contain an X chromosome while sperm contain either X or Y chromosomes. When the X egg is fertilised with an X sperm, the XX chromosome makeup makes a girl. When the X egg is fertilised with a Y sperm, the XY chromosome makeup makes a boy. Therefore the baby has a 50/50 chance of being a girl or boy, and it is the sperm that determines the baby's gender. 

9.2: Cell Division

1. Define mitosis

Mitosis: nuclear division giving rise to genetically identical cells in which the chromosome number is maintained by the exact duplication of chromosomes.

Mitosis begins with a single cell, so it contains 46 chromosomes (23 pairs). This is known as the diploid parent cell. The cell makes a copy of each chromosome, resulting in 92 chromosomes. It then divides itself in half, forming two new cells that each contain a full set of chromosomes and are identical to the parent cell. They are known as the daughter diploid cells.

Gotta love that comic sans!

What type of cells go through mitosis? Body cells! The daughter cells end up with a full set of chromosomes, and we know that body cells are diploid nucleuses.


2. Sate the role of mitosis in growth, repair of damaged tissues, replacement of worn out cells and asexual reproduction.

As said above, mitosis is used to provide body cells that replace old or dead ones. It is also used for asexual reproduction, as asexual reproduction produces a clone of the parent with the exact same genetic makeup.


3. Define meiosis

Meiosis: reduction division in which the chromosome number is halved from diploid to haploid.

Meiosis is similar to mitosis. The process is the same until the end; the two daughter cells split in half again, resulting in four cells that contain 23 chromosomes each.

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4. State that gametes are the result of meiosis.

Gametes are the result of meiosis. *Heh* We know that gametes contain 23 chromosomes each, and meiosis results in four cells that contain 23 chromosomes each. It adds up!

5. State that meiosis results in genetic variation so the cells produced are not all genetically identical.

To form a zygote, you need an egg and sperm. Both of these gametes contain different genetic information, so through meiosis genetic information is shared and split between the cells. This results in genetic variation, where cells don't all contain the same genetic information.

This can be beneficial as if the parent has a disease, it could potentially be passed down to the child; genetic variation makes it so that the disease has a chance of not being passed.

Chemistry Unit 8: Acids, Bases and Salts

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Unit 8.1 The characteristic properties of acids and bases

Before I start going into the syllabus, let's define acids and bases clearly!

Acids: a substance that dissolves in water to produce hydrogen

Base: a substance that neutralises an acid

A lot of the time, you'll hear the word alkali. An alkali is a type of base that can dissolve in water. An alkali is a base, but a base is not an alkali.

1. Describe neutrality and relative acidity and alkalinity in terms of pH (whole numbers only) measured using full-range indicator and litmus.

When talking about pH, you've got the whole pH scale in mind, where you identify the pH according to a certain colour. You can use litmus paper or universal indicator (UI) to check a substance's pH. 

Neutral: pH 7, turns UI green, turns litmus paper purple

Acid: low pH (less than 7), turns UI red-yellow, turns litmus paper red

Alkali: high pH (greater than 7), turns UI blue-purple, turns litmus paper blue

Below is an image displaying the different colours universal indicator turns according to pH levels, and also what substances are of that pH level.

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2. Describe the characteristic reactions between acids and metals, bases (including alkalis) and carbonates.

Here is a handy-dandy four-step system to this:

● acid + alkali --> salt + water

● acid + metal --> salt + hydrogen

● acid + carbonate --> salt + water + carbon dioxide

● acid + oxides (bases) --> salt + water

3. Describe and explain the importance of controlling acidity in the environment (air, water and soil)

Soil: Soil is used to grow crops, so it is important for it to be neutral. If it happens to be too alkaline or acidic, the crops tend to grow poorly. Acidity is usually the problem for soil, so a base can help neutralise it. Bases include limestone, slaked lime, or quick lime (more on that later!).

Water: Factory waste is often acidic, and it can leak into water. To prevent this from happening, it needs to be neutralised. Again, slaked lime is used for this. 

Air: Burning fossil fuels releases gases into the air, such as nitrogen oxides and sulphur dioxide. They react with water and air, leading to acid rain. As you can tell by the name, it's not that great; it causes buildings to erode and will negatively affect soil and water. 

Unit 8.2 Types of oxides

1. Classify oxides as either acidic or basic, related to metallic and non-metallic character of the other element.

First, let's define oxide: it is a compound made up of oxygen and another element. Next, acidic oxide: a compound of oxygen and a non-metal, most commonly a gas. Lastly, basic oxide: a compound of oxygen and a metal.

Here are some examples of each type of oxide:
acidic oxide: sulphuric acid (H2SO4), nitric acid (HNO3)
basic oxide: sodium hydroxide (NaOH), copper oxide (CuO)

So now that you know what the different oxides are, it's easier to classify them into groups. 

Acidic oxides:
● react with water to give and acid
i.e carbon dioxide + water --> carbonic acid
     CO2 + H2O --> H2CO3
● react with bases to form a salt
i.e. sulphuric acid + copper oxide --> copper sulphate + water
     H2SO4 + CuO --> CuSO4 + H2O

Basic oxides:
● react with acids to form a salt and water
i.e. copper oxide + hydrochloric acid --> copper chloride + water

     CuO + 2HCl --> CuCl2 + H2O


2. Further classify some oxides as neutral, given relevant information.

Some oxides are neither basic or acidic, so they are neutral oxides. They don't react with acids or bases either. Examples of neutral oxides include nitrous oxide (N2O) and carbon monoxide (CO). 




Unit 8.3 Preparation of salts

1. Describe the preparation, separation and purification of salts using techniques selected from section C2.1 and the reactions specified in C8.1.

Preparing the salt:
1. Add an excess of your carbonate to your acid
2. Test the pH with U.I. paper to check if the solution is neutral
3. Filter the solution to get rid of the excess carbonate
4. Heat the liquid until most of it has evaporated and you are left with salt crystals

Separating the salt:
Let's say we have a mixture of salt and pebbles
1. Add water to your mixture so the salt dissolves
2. Filter the mixture
3. Evaporate the liquid

Purifying the salt:
If it's an insoluble salt: filtration
If it's a soluble salt: distillation

2. Suggest a method of making a given salt from suitable starting materials, given appropriate information. 

Remember that handy-dandy four-step system from above? Here, it comes to use.

Acid + alkali --> salt + water
Hydrochloric acid + sodium hydroxide --> sodium chloride + water
HCl + NaOH --> NaCl + H2O
1. Add 30cm2 of sodium hydroxide to a flask
2. Add two drops of the indicator phenolphthalein 
3. Add the hydrochloric acid to the flask
4. The solution will turn colourless when neutralised
5. Heat the solution to evaporate the liquid and obtain the salt

Acid + metal --> salt + hydrogen
Sulphuric acid + zinc --> zinc sulphate + hydrogen
H2SO4 + Zn --> ZnSO4 + H2
1. Add zinc to a flask of the acid
2. When the zinc dissolves, hydrogen bubbles will appear
3. Filter the solution to remove the excess zinc
4. Heat the solution to evaporate the liquid and obtain the salt

Acid + base --> salt + water
Sulphuric acid + iron(II) oxide --> iron sulphate + water
H2SO4 + FeO --> FeSO4 --> H2O
1. Add and excess of iron oxide to the sulphuric acid
2. Filter the solution to remove the excess iron oxide
3. Heat the solution to evaporate the liquid and obtain the salt




Unit 8.4 Identification of ions and gases

1. Use the following tests to identify aqueous cations, anions, and gases.

Aqueous cations:
● ammonium
● copper(II)
● iron(II)
● iron(III)
● zinc 

Cation	Test	What happens if cation is present?
Ammonium	Add dilute sodium hydroxide, warm up	Ammonia gas is released, damp red litmus paper turns blue
Copper(II)	Add dilute sodium hydroxide or ammonia solution	A blue precipitate forms
Iron(II)	Add dilute sodium hydroxide or ammonia solution	A pale green precipitate forms
Iron(III)	Add dilute sodium hydroxide or ammonia solution	A red-brown precipitate forms
Zinc	Add dilute sodium hydroxide or ammonia solution	A white precipitate forms

Anions:

● carbonate

● chloride

● nitrate

● sulphate

Anion	Test	What happens if anion is present?
Carbonate	Add dilute hydrochloric acid	Bubbles that give off gas turn limewater a milky-white
Chloride	Add the same volume of nitric acid as chloride, add aqueous silver nitrate	A white precipitate forms
Nitrate	Add sodium hydroxide, then aluminium	Ammonia gas will be given off
Zinc	Add dilute sodium hydroxide or ammonia solution	A white precipitate forms

Gases:

● ammonia

● carbon dioxide

● chlorine

● hydrogen

● oxygen

Anion	Test	What happens if gas is present?
Ammonia	Damp red litmus paper	Paper turns blue
Carbon dioxide	Limewater	Limewater turns milky-white
Chlorine	Damp blue litmus paper	Paper turns white
Hydrogen	Lighted splint	A loud POP
Oxygen	Glowing splint	Splint relights