Physics Made Simple : Electrostatics : Electrostatic Shielding

Electrostatic Shielding :

It is the process of isolating a certain region of space from external field.

It is based on the fact that electric field inside a conductor is zero.




Electrostatic Induction :

Electrostatic induction is a method to create or generate static electricity in a material by bringing an electrically charged object near it. This causes the electrical charges to be redistributed in the material, resulting in one side having an excess of either positive (+) or negative (−) charges.

It is possible to obtain charges without any contact with another charge.

They are known as induced charges and the phenomenon of producing induced charges is known as electrostatic induction.

It is used in electrostatics machines such as Van de Graaff generator and capacitors.



Capacitance of a conductor :

The capacitance of a conductor is defined as the ration of the charge given to the conductor to the potential developed in the conductor.

Physics Made Simple : Electrostatics : Electric Flux

The Electric Flux:

This is defined as the total number of electric lines of force crossing through the given area.

Gauss"s Law :

This law relates the flux through any closed surface and the net charge enclosed with in the surface.

This law applies to:

1 . Electric field due to an infinite long straight charged wire

2. Electric Field due to an infinite charged plane sheet.

3.Electric field due to two parallel charged sheets.

4. Electric field due to uniformly charged spherical shell.


Electrostatic Shielding :

It is the process of isolating a certain region of space  from an external field.

It is based on the fact that electric field inside a conductor is zero.

Physics Made Simple : Electrostatics : Electric Field

Electric Field:

The electric field due to a charge is the space around that charge where it experiences a force.

The presence of an electricfield around a charge cannot be detected unless another charge is brought towards it.

If a test charge g is placed near a charge q which being the source of electric field, an electrostatic force F will act on the test charge.

Electric Field Intensity :

Electric field at a point is measured in terms of  electric field intensity.

Electric field intensity at a point in an electric field is defined as the force experienced by a unit positive charge kept at that point.

Electric lines of force :

Electric line of force is an imaginary straight or curved path along which a unit positive charge tends to move in an electric field.

Endocrinology Made Simple : Sheehan Syndrome

Sheehan"s syndrome :

This refers to hypopituitarism due to ischemic damage to the pituitary resulting from excessive haemorhage during delivery / parturition.

During pregnancy,the pituitary gland gets enlarged and metabolically more active and more susceptible to hypoxemia.

The blood vessels in pituitary are more suseptible to vasospasm due to excessive estrogen levels.

The clinical presentation depends on how much the pituitary gland has been damaged and the type of cells damaged.

For example damage to pituitary gonadotrophs and diminished secretion of gonadotrophs / LH may lead to Amenorrhoea.

Damage to lactotrophs will lead to reduced prolactin levels.

If the patient tries to breast feed her child in this case,most likel failure of lactation would be seen.

Damage to Corticotrophs will affect steroids metabolism and ACTH levels.

Hypothyroidism is also common

Clinical Genetics Made Simple : X - linked Disorders : Wiskott - Aldrich Syndrome

 X - linked Disorders : Wiskott - Aldrich Syndrome :

This is an X linked disorder.

Mutations in the WASP gene on short arm of X chromosome are responsible for this disease.

It is characterized by eczema,thrombocytopenia and repeated infections.

Affected children may present with bleeding and often succumb to complications of bleeding,infection or lymphoreticular malignancy.

The platelets are small,have a shortened half-life and appear to be deficient in surface sialophorin ( CD43).

Splenectomy can correct the thrombocytopenia but not the immune defect.

Serum IgM is usually decreased while IgE is frequently increased.


Other diseases with immune defects include :

Selective IgA deficiency.

DiGeorge Syndrome :

Characterized by developmental malformation leading to thymic aplasia and hypoparathyroidism.


Ataxia Telangiectasia :

An autosomal recessive disease characterized by progressive cerebellar dysfunction,telangiectasias and a variable immunodeficiency.

Acquired Hypogammaglobulinemia:

This disease is seen in adults.
It ischaracterized by normal number of B cells but low immunoglobulin production.

Physics Made Simple : Electrostatics : Coulombs Law

Coulomb"s Law :

This law states that the force of attraction or repulsion between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.


Electric Field :

The electric field due to a charge is the space around the test charge in which it experiences a force.
The presence of an electric field around a charge cannot be detected unless another charge is brought towards it.

Electric field Intensity :

The electric field intensity at a point in an electric field is defined as  the force experienced by a unit positive charge kept at that point

It is a vector quantity.

It can also be referred as Electric field strength or simply electric field

Physics Made Simple : Electrostatics :Conductors & Insulators

Electrostatics

Electrostatics is a branch of physics which deals with static electric charges or charges at rest.

Main characteristics of static electric charges:

The charges in an electrostatic field are similar to masses in a gravitational field.

These charges have forces acting on them and hence possess potential energy.

Like charges repel each other and unlike charges attract each other.

Conductors

Conductors are bodies that allow the charges to pass through them. eg metals

Insulators

Insulators are bodies that do not allow the charges to pass through them eg glass ,mica,plastic etc

Basic Properties of electric charge :

Quantisation of electric charge :

The fundamental unit of electric charge (e) is the charge carried by the electron and its unit is Coulomb.

e has a magnitude of 1.6 * 10 ^ 19 C

Conservation of Electric charge:

Electric charges can neither be created nor destroyed.

According to this law,the total charge in an isolated system remains constant.

The charges can be transferred from one part of the system to another but the total charge in a system always remain constant.

Additive properties of charge :

The total electric charge of a system is the algebric sum of electric charges in the system

Clinical Medicine Made Simple : Clinical manifestations of vitamin Deficiencies

Thiamine Deficiency:

This  leads to Wernicke - Korsakoff Syndrome,which is a constellation of neurologic symptoms which include severe memory deficit,confabulation which means patient makes up imaginary stories to cover his memory deficit.These occur due to damage to mamillary bodies and periventricular structures

Thiamine deficiency can also damage the peripheral nerves : DryBeri beri and heart / Wet beri beri

Folic Acid Deficiency :

This produces Megaloblastic Anemia without neurologic symptoms

Niacin Deficiency :

This produces Pellagra characterized by depigmenting dermatitis,chronic diarrhea and anemia

Riboflavin deficiency:

This produces ariboflavinosis which is characterized by glossitis,corneal opacities,dermatitis and erythroid hyperplasia

Vitamin B12 Deficiency :

This produces megaloblastic anemia accompanied by degeneration of posterolateral spinal cord.