11) Magbetic Field and Properties of Tissues Flashcards
Magnetic field
It’s generated by moving electrical charges
Any electric current causes a magnetic field
Magnetic induction
Magnetic induction B is the vector describing the direction and magnitude of the magnetic field
Graphic representation of magnetic field
The magnitude of the field line is proportional to the density of the field line
Magnetic field lines are closed loops
Direction of magnetic induction
Pointing the right hand thumb in the direction of the moving positive charge and the rest of the fingers in the direction of the magnetic field
Magnitude of the magnetic induction
dB= u_o/4 pi x IdL/r^2 x sinø
Current is I
r is the distance
U_o is free space
Lorentz force
Acts on charges moving in a magnetic field
Depends on magnitude of induction B
Magnitude Q
Velocity V
F=qvBsinø
Work of magnetic force
Magnetic force can do no work as it is perpendicular to the direction of movement
It’s not conservative
Movement of charged particles in a magnetic field
The Lorentz force acts as a centripetal force
The particle performs circular motion
DAWING
Application examples
The radius of circle depends the mass, velocity, charge
It’s used to control movement of charges particles in electron microscopy and mass spectrometers
Forces between current carrying wires
Current carrying wires interact with each other by magnetic force
Any current carrying wire includes a magnetic field
Ampere’s force law
The interaction force between 2 current elements is
dF= u_o (IdL)(I2dL2)/4pi r^2 sinø1sinø2
2 parallel wires attract each other if their currents flow in the same direction
Current is measured in amps
Magnetic dipole moment of a current loop
Direction is determined by the right hand grip rule
Magnitude is P_m=IS
Torque on magnetic dipole
In external magnetic fields a couple is generated
Magnetic moment aligns with the field lines
Orbital magnetic moment Of electron
Electron with
Charge e
Velocity v
Radius r
P_mo=1/2evr
Spin magnetic moment of the electron
P_ms=h/4pi e/m
h is planks constant
e and m is the charge and mass of the electron
Magnetic properties of matter
Determined by orbital and spin magnetic moments of the electron
The net magnetic moment of an atom is the vectorial sum of the orbital and spin magnetic moment of its electrons
Diamagnetic materials
Examples
Water
Co2
Nitrogen
They have no magnetic field of their own
Diamagnetic effect
Induction of a magnetic field inside the material in opposition of an externally applied magnetic field
Diamagnetic in a magnetic field
The diamagnetic field inside the body is weaker than the external field
Magnets exert a repulsive force of diamagnetic bodies
Paramagnetic materials
Examples
Aluminium
Liquid oxygen
Free radicals
They have no magnetic field of their own as the magnetic moments cancel out
Paramagnetic effect
Generation on magnetic field inside the material in the direction of an externally applied magnetic field
Paramagnetic in a magnetic field
The paramagnetic inside the material is stronger than the external
The magnets exert an attraction force on the paramagnetic body
Ferromagnetic materials
Examples
Iron
Cobalt
Nickel
They are paramagnetic substances consisting of numerous magnetic domains. Above a certain temp the domains are destroyed and become ordinary paramagnetic materials
Ferromagnetic effect
The internal magnetic field becomes much stronger than the external
External magnetic field aligns the magnetic domains
Magnetic hysteresis
The internal magnetic field changes and takes different paths when external field is decreased or increased
Applications of ferromagnetic
Used for the generation of string magnetic fields
Extraction of ferromagnetic particles out of the eye
Magnetic properties of biological tissue
Most biological tissues have diamagnetic properties
The human body contains some paramagnetic atoms molecules ions and radicals
Ferromagnetic material in the body is negligible
Effect of magnetic field on the human body
Mechanical vibrations of nerve and muscle fibres
Magnetohydrodynamics slows down blood flow
Magnetocardiography
Non contact method for investigation of the heart
