It is a known fact that well-insulated buildings need less energy for heating than do buildings that have no insulation. Two building materials that are being used more and more worldwide, are
mineral wool and
polystyrene . Mineral wool is a good insulator because it holds air still in the matrix of the wool so that heat is not lost. Since air is a poor conductor and a good insulator, this helps to keep energy within the building. Polystyrene is also a good insulator and is able to keep cool things cool and hot things hot. It has the added advantage of being resistant to moisture, mould and mildew.
Remember that concepts such as conductivity and insulation are not only relevant in the building, industrial and home environments. Think for example of the layer of blubber or fat that is found in some animals. In very cold environments, fat and blubber not only provide protection, but also act as an insulator to help the animal keep its body temperature at the right level. This is known as
thermoregulation .
Magnetic and non-magnetic materials
We have now looked at a number of ways in which matter can be grouped, such as into metals, semi-metals and non-metals; electrical conductors and insulators, and thermal conductors and insulators. One way in which we can further group metals, is to divide them into those that are
magnetic and those that are
non-magnetic.
Magnetism
Magnetism is one of the phenomena by which materials exert attractive or repulsive forces on other materials.
A metal is said to be
ferromagnetic if it can be magnetised (i.e. made into a magnet). If you hold a magnet very close to a metal object, it may happen that its own electrical field will be induced and the object becomes magnetic. Some metals keep their magnetism for longer than others. Look at iron and steel for example. Iron loses its magnetism quite quickly if it is taken away from the magnet. Steel on the other hand will stay magnetic for a longer time. Steel is often used to make permanent magnets that can be used for a variety of purposes.
Magnets are used to sort the metals in a scrap yard, in compasses to find direction, in the magnetic strips of video tapes and ATM cards where information must be stored, in computers and TV's, as well as in generators and electric motors.
Investigation : magnetism
You can test whether an object is magnetic or not by holding another magnet close to it. If the object is attracted to the magnet, then it too is magnetic.
Find some objects in your classroom or your home and test whether they are magnetic or not. Then complete the table below:
Object
Magnetic or non-magnetic
Group discussion : properties of materials
In groups of 4-5, discuss how our knowledge of the properties of materials has allowed society to:
develop advanced computer technology
provide homes with electricity
find ways to conserve energy
The following presentation provides a summary of the classification of matter.
Summary
All the objects and substances that we see in the world are made of
matter .
This matter can be classified according to whether it is a
mixture or a
pure substance .
A
mixture is a combination of one or more substances that are not chemically bonded to each other. Examples of mixtures are air (a mixture of different gases) and blood (a mixture of cells, platelets and plasma).
The main
characteristics of mixtures are that the substances that make them up are not in a fixed ratio, they keep their individual properties and they can be separated from each other using mechanical means.
A
heterogeneous mixture is non-uniform and the different parts of the mixture can be seen. An example would be a mixture of sand and water.
A
homogeneous mixture is uniform, and the different components of the mixture can't be seen. An example would be a salt solution. A salt solution is a mixture of salt and water. The salt dissolves in the water, meaning that you can't see the individual salt particles. They are interspersed between the water molecules. Another example is a metal
alloy such as steel.
Mixtures can be
separated using a number of methods such as filtration, heating, evaporation, centrifugation and dialysis.
Pure substances can be further divided into
elements and
compounds .
An
element is a substance that can't be broken down into simpler substances through chemical means.
All the elements are recorded in the
Periodic Table of the Elements . Each element has its own chemical symbol. Examples are iron (
), sulphur (
), calcium (
), magnesium (
) and fluorine (
).
A
compound is a substance that is made up of two or more elements that are chemically bonded to each other in a fixed ratio. Examples of compounds are sodium chloride (
), iron sulphide (
), calcium carbonate (
) and water (
).
When
naming compounds and writing their
chemical formula , it is important to know the elements that are in the compound, how many atoms of each of these elements will combine in the compound and where the elements are in the Periodic Table. A number of rules can then be followed to name the compound.
Another way of classifying matter is into
metals (e.g. iron, gold, copper),
semi-metals (e.g. silicon and germanium) and
non-metals (e.g. sulphur, phosphorus and nitrogen).
Metals are good electrical and thermal conductors, they have a shiny lustre, they are malleable and ductile, and they have a high melting point. These properties make metals very useful in electrical wires, cooking utensils, jewellery and many other applications.
A further way of classifying matter is into
electrical conductors ,
semi-conductors and
insulators .
An
electrical conductor allows an electrical current to pass through it. Most metals are good electrical conductors.
An
electrical insulator is not able to carry an electrical current. Examples are plastic, wood, cotton material and ceramic.
Materials may also be classified as
thermal conductors or
thermal insulators depending on whether or not they are able to conduct heat.
Materials may also be either
magnetic or
non-magnetic .
Summary
For each of the following
multiple choice questions, choose
one correct answer from the list provided.
Which of the following can be classified as a mixture:
sugar
table salt
air
iron
An element can be defined as:
A substance that cannot be separated into two or more substances by ordinary chemical (or physical) means
A substance with constant composition
A substance that contains two or more substances, in definite proportion by weight
A uniform substance
Classify each of the following substances as an
element , a
compound , a
solution (homogeneous mixture), or a
heterogeneous mixture : salt, pure water, soil, salt water, pure air, carbon dioxide, gold and bronze.
Look at the table below. In the first column (A) is a list of substances. In the second column (B) is a description of the group that each of these substances belongs in. Match up the
substance in Column A with the
description in Column B.
Column A
Column B
iron
a compound containing 2 elements
H
2 S
a heterogeneous mixture
sugar solution
a metal alloy
sand and stones
an element
steel
a homogeneous mixture
You are given a test tube that contains a mixture of iron filings and sulphur. You are asked to weigh the amount of iron in the sample.
Suggest one method that you could use to separate the iron filings from the sulphur.
What property of metals allows you to do this?
Given the following descriptions, write the chemical formula for each of the following substances:
silver metal
a compound that contains only potassium and bromine
a gas that contains the elements carbon and oxygen in a ratio of 1:2
Give the names of each of the following compounds:
For each of the following materials, say what properties of the material make it important in carrying out its particular function.
tar on roads
iron burglar bars
plastic furniture
metal jewellery
clay for building
cotton clothing
Questions & Answers
What are the factors that affect demand for a commodity
In economics, a perfect market refers to a theoretical construct where all participants have perfect information, goods are homogenous, there are no barriers to entry or exit, and prices are determined solely by supply and demand. It's an idealized model used for analysis,
When MP₁ becomes negative, TP start to decline.
Extuples Suppose that the short-run production function of certain cut-flower firm is given by: Q=4KL-0.6K2 - 0.112 •
Where is quantity of cut flower produced, I is labour input and K is fixed capital input (K-5). Determine the average product of lab
Kelo
Extuples Suppose that the short-run production function of certain cut-flower firm is given by: Q=4KL-0.6K2 - 0.112 •
Where is quantity of cut flower produced, I is labour input and K is fixed capital input (K-5). Determine the average product of labour (APL) and marginal product of labour (MPL)
Quantity demanded refers to the specific amount of a good or service that consumers are willing and able to purchase at a give price and within a specific time period. Demand, on the other hand, is a broader concept that encompasses the entire relationship between price and quantity demanded
Ezea
ok
Shukri
how do you save a country economic situation when it's falling apart
Economic growth as an increase in the production and consumption of goods and services within an economy.but
Economic development as a broader concept that encompasses not only economic growth but also social & human well being.
Shukri
production function means
Jabir
What do you think is more important to focus on when considering inequality ?
sir...I just want to ask one question... Define the term contract curve? if you are free please help me to find this answer 🙏
Asui
it is a curve that we get after connecting the pareto optimal combinations of two consumers after their mutually beneficial trade offs
Awais
thank you so much 👍 sir
Asui
In economics, the contract curve refers to the set of points in an Edgeworth box diagram where both parties involved in a trade cannot be made better off without making one of them worse off. It represents the Pareto efficient allocations of goods between two individuals or entities, where neither p
Cornelius
In economics, the contract curve refers to the set of points in an Edgeworth box diagram where both parties involved in a trade cannot be made better off without making one of them worse off. It represents the Pareto efficient allocations of goods between two individuals or entities,
Cornelius
Suppose a consumer consuming two commodities X and Y has
The following utility function u=X0.4 Y0.6. If the price of the X and Y are 2 and 3 respectively and income Constraint is birr 50.
A,Calculate quantities of x and y which maximize utility.
B,Calculate value of Lagrange multiplier.
C,Calculate quantities of X and Y consumed with a given price.
D,alculate optimum level of output .
the market for lemon has 10 potential consumers, each having an individual demand curve p=101-10Qi, where p is price in dollar's per cup and Qi is the number of cups demanded per week by the i th consumer.Find the market demand curve using algebra. Draw an individual demand curve and the market dema
suppose the production function is given by ( L, K)=L¼K¾.assuming capital is fixed find APL and MPL. consider the following short run production function:Q=6L²-0.4L³ a) find the value of L that maximizes output b)find the value of L that maximizes marginal product
Abdureman
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