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Wednesday, March 31, 2010

general science#10

PHYSICS: HEAT

Overview

  • Heat is the process of energy transfer from one system to another
  • Units of heat: Joules (J), Calories, British Thermal Unit (BTU)
  • Temperature is a measure of internal energy (enthalpy)
  • Heat transfer can happen spontaneously only from a warmer to a colder body. Reverse heat transfer can only happen with the aid of an external source such as a heat pump.
Mechanisms of heat transfer

  • Conduction is the most significant heat transfer mechanism in solids. It occurs as hot high energy molecules interact with neighbouring and transfer heat to them. Eg: heat transfer from one end of a metal rod to another
  • Convection is most significant in liquids and gases. This happens when hot molecules move and transfer energy to other molecules. Eg: boiling of water. When water is heated on a stove, hot water from the bottom rises and displaces colder liquid which falls.
  • Radiation is the only form of heat transfer possible in the absence of a medium. Heat is transferred in the form of electromagnetic radiation. Eg: heat from the sun reaching the earth.
Heat transfer in everyday life

  • Copper is used in construction of boilers and cooking utensils because it is a good conductor of heat
  • Air is a poor conductor
  • Wool and cotton are good insulators i.e. poor conductors. Their insulation arises mainly due to air spaces between molecules
  • Double-walled glass doors with air between them are better insulators than windows with a single thick glass layers
  • Eskimos live in snow huts because snow is a poor conductor of heat, and hence protects them from the extreme cold outside.
  • Land and sea breeze, ocean currents are arise due to convection
  • The boiling point of water at sea level and atmospheric pressure is 100C. When extra heat is added, it changes the phase of water from liquid to gas (water vapour).
Thermometers

  • Thermometers can be divided into two groups:
    • Primary thermometers: measure temperature directly based on the property of matter. They are relatively complex and not used commonly. Eg: thermometers based on velocity of sound in gas, thermal noise of an electrical resistor etc.
    • Secondary thermometers: measure temperature relative to a pre-calibrated quantity. They are easy to use and used commonly. Alcohol thermometer, mercury thermometer, medical thermometer are all secondary thermometers
  • In cold winter places, alcohol thermometers are used instead of mercury thermometers because the freezing point of alcohol is lower
  • For extra-low temperature measurements (-200 C), Pentane is used
  • Water is not suitable for use in thermometers because it freezes at 0 C and has irregular expansion
  • Mercury is used for common medical thermometers because
    • It does not cling to glass and hence reading is easy
    • It is opaque and easily seen
    • Its expansion is uniform and hence calibration is easier
    • It is a better conductor of heat than alcohol and hence responds more rapidly to changes of temperature
    • It has low specific heat capacity and hence is more sensitive
Common appliances based on heat

  • Solar cooker: is a box made of insulating material such as wood, cardboard etc. The box has a glass cover to retain heat inside by greenhouse effect. The inside of the box is painted black to increase heat absorption.
  • Pressure cooker: Pressure cooker increases the boiling point of water by increasing pressure. When the boiling point of water increases, food cooks faster. Pressure cookers are especially essential in hill stations because at higher altitudes the boiling point of water decreases due to lower atmospheric pressure
  • Refrigerator and Air-conditioner: are heat pumps that transfer heat from inside to the external environment. They use a refrigerant which is a compound that undergoes reversible phase change from gas to liquid. Common refrigerants include ammonia, sulphur dioxide, carbon dioxide and methane. The use of chlorofluorocarbons has been phased out due to concerns regarding depletion of the ozone layer.

CHEMISTRY: ELECTROLYTES

Electrolytes in the human body

  • Electrolytes are required in the body to maintain balance between intracellular and extracellular liquids. In particular, it is important to maintain the osmotic gradient between inside and outside.
  • Electrolyte balance is maintained by oral and intravenous intake
  • Kidneys flush out excess electrolytes
  • Dehydration and overhydration are caused by electrolyte imbalance
  • Hormones that maintain electrolyte balance are antidiuretic hormone, aldosterone and parathyroid hormone
  • The most common electrolyte in the body is salt (sodium chloride)
Functions of electrolytes in the body

  • Maintain blood pH
  • Muscle and neuron activation
  • Hydration of the body
Other common applications of electrolytes

  • Sports drinks
  • Batteries
  • Fuel cells
  • Electroplating
  • Capacitors
Sports Drinks

  • Sports drinks replenish the body’s water and electrolyte levels after dehydration caused by exercise, vomiting, diarrhea etc.
  • They are made of electrolytes containing sodium and potassium salts
  • Examples of sports drinks: Glucon-D, Gatorade etc
  • Simplest electrolyte drink that can be made at home is water + sugar + salt
Batteries

Battery
Electrode
Electrolyte
Other notes
Alkaline
Zinc, Manganese oxide
Potassium Hydroxide





Daniell cell
Copper, Zinc
Copper sulphate, zinc sulphate





Leclanche cell
Zinc, carbon
Ammonium chloride
Precursor of modern dry cell




Voltaic pile
Copper, zinc
Brine
First electric battery, invented in 1880




Zinc carbon
Zinc, carbon, manganese dioxide
Zinc chloride, ammonium chloride
Most common battery




Zinc chloride
Same as above
Zinc chloride
Improvement on zinc carbon battery




Lead-acid
Lead, lead dioxide
Sulphuric acid
Oldest rechargeable battery
Used in vehicles as they provide high surge currents




Lithium-ion
Graphite, Lithium Cobalt oxide
Non-aqueous lithium salts
Rechargable
Slow self-discharge, high energy to weight ratio




Nickel Cadmium
Nickel oxide hydroxide, cadmium

Rechargable
Last longer, more stable than lithium ion




Fuel cell
Hydrogen (fuel), oxygen (oxidant)
Polymer membrane
Aqueous alkaline solution
Consumes reactant from an external source
High energy efficiency and high reliability
No moving parts
Used in space shuttles, submarines
Common electrolytes and their uses

Electrolyte
Uses
Other notes
Sodium chloride
Primary component of extracellular fluid
Food preservative




Sodium hydroxide
(caustic soda)
Manufacture of paper, soaps, detergents, drain cleaners
Purification of drinking water




Silver nitrate
Photographic films
Water disinfection (esp. on space shuttles)




Hydrochloric acid
Manufacture of PVC, household cleaners
Food additives (like gelatin)
Leather processing
Found naturally in gastric acid



Sulphuric acid
Lead-acid batteries
Ore processing
Fertilizer manufacture
Soluble in water at all concentrations
One of the largest products of chemical industry



Nitric acid
Determining metal traces in solutions
Wood finishing
Colourless when pure, yellows with age
Highly corrosive



Acetic acid
Manufacture of soft drink bottles
Photographic films
Synthetic fibres and fabrics
Dilute acetic acid is called vinegar



Ammonium hydroxide
(aqueous ammonia)
Cleaning agent




Calcium hydroxide
(slaked lime or pickling lime)
Sewage treatment
Whitewash, plaster, mortar
Hair relaxers
Natural mineral form is called portlandite
(rare mineral occurring in volcanic rocks)

BIOLOGY: BLOOD

Overview

  • Blood is a specialized body fluid that delivers necessary substances to various cells (like nutrients and oxygen) and transports waste products away from those cells
  • Blood accounts for 7% of human body weight
  • The average human adult has a blood volume of approx. 5 litres
  • Arteries carry inhaled oxygen-rich blood from the heart to the tissues, while veins carry carbon dioxide rich blood (de-oxygenated) from the tissues to the lungs to be exhaled
Red_White_Blood_cells
SEM image of a RBC, a platelet and a WBC (L to R)
Composition of blood
  • Blood is made of plasma, Red Blood Cells, White Blood Cells (including leukocytes and platelets)
  • Plasma constitutes about 54.3% of blood, RBCs 45% and WBCs about 7%
  • RBCs contain hemoglobin and distribute oxygen to tissues
  • Leukocytes attack and remove pathogens and provide immunity
  • Platelets are responsible for clotting of blood
  • Plasma is the blood’s liquid medium. It circulates dissolved nutrients and removes waste products. By itself, it is yellow in colour
Functions of blood

  • Supply oxygen to tissues
  • Supply nutrients such as glucose, amino acids and fatty acids
  • Remove waste such as carbon dioxide, urea and lactic acid
  • Provide immunity against pathogens
  • Coagulation
  • Transport hormones
  • Regulate pH
  • Regulate core body temperature
Colour of blood

  • Colour is primarily determined by hemoglobin
  • Arterial blood is bright red, due to the presence of oxygen
  • Venous blood is dark red, due to deoxygenation
  • Blood in carbon monoxide and cyanide poisoning is bright red
  • Blood of most molluscs (marine animals like squids, oysters, snails, octopuses etc) is blue due to the presence of copper containing protein hemocyanin
Blood Groups

Blood Group
Can donate to
Can receive from
A
A and AB
A and O



B
B and AB
B and O



AB
AB only
All groups



O
All groups
O only
Medical disorders related to blood

Disorder
Cause
Other notes
Bleeding
An adult can lose 20% of blood volume before the first symptom (restlessness) sets in



Dehydration
Loss of volume due to loss of water




Atherosclerosis
Reduced blood flow through arteries




Thrombosis
Coagulation of blood vessels




Hypoxia (lack of oxygen)
Narrowing of blood vessels
Problem with pumping action of heart
Can lead to ischemia (tissue with insufficient blood) or to infarction i.e. necrosis (tissue death)



Anemia (insufficient RBC)
Bleeding, nutritional deficiencies




Sickle-cell disease
Mutation of hemoglobin leading to abnormal sickle shape of RBC
Sickle shaped RBCs do not have the flexibility to travel through many blood vessels
Extremely painful disease with no known cure
Found commonly in malaria-infested areas because sickle cells offer resistance to malaria



Leukemia
Abnormal proliferation of WBCs in the bone marrow




Hemophilia
Dysfunction of clotting mechanism
Lack of coagulation means simple wounds become life-threatening
Causes hemarthosis (bleeding into joints), which is painful and crippling
Linked to X chromosome
Occurs usually in males only



Thrombophilia
Abnormal propensity to coagulate




Blood-borne infections
Infection by a disease-carrying vector
Examples: HIV, Hepatitis, Malaria



Carbon monoxide poisoning
Carbon monoxide binds to hemoglobin preventing oxygen transport
Body tissues die due to lack of oxygen

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