✧ vsaqs

• power of the lens is the reciprocal of focal length.

  units are dioptre.
• when the image forms behind the retina it is called as hypermetropia.

  it is corrected by convex lens.
• when an object is placed at the near point but the image is formed just in front of the retina, it is called as myopia.

  it is corrected with diverging lens called as concave lens.
• the phenomena of splitting of white light into different colors when passing through a thick glass medium is called as dispersion. violet color gets deviated more.
• ammeter is an instrument used to measure current.
• voltmeter is used to measure potential difference.
• ammeter offers low resistances and is always connected in series.
• voltmeter offers very high resistances and is always connected in parallel.
• ideal resistance of ammeter is 0
• ideal resistance for voltmeter is infinity.
• principle of moving coil galvanometer ;

  when a current carrying rectangular coil is freely suspended inside a uniform magnetic field, it undergoes couple and restoring couple due to which it oscillates for sometime before coming to rest.
• importance of oersted experiment ;

  it led to the discovery of electromagnetism and explains the relationship between electricity and magnetism.
• you can convert a moving coil galvanometer into an ammeter by connecting a small resistance 'shunt' parallel to it.
• ampere's law ; helps us to find out magnetic induction field strength due to a current carrying wire.
• biot savart's law ; the magnetic induction field strength due to a small segment of infinitely long wire at a point is directly proportional to strength of the wire, length of the wire, sin angle between the segment & the line joining the point & inversely proportional to the square of the distances between the point and the segment.
• manganese and oxygen are paramagnetic.
• cobalt and nickel show ferromagnetism.
• bismuth is diamagnetic.
• copper is non magnetic in nature.
• magnetic inclination/angle of dip ;

  it is the angle between the direction of total magnetic field of earth and a horizontal line in magnetic meridian.
• magnetic lines of force form continuous closed loops because magnetic monopoles do not exist in nature.
• compass needle points north poles and magnetic needle is used to detect poles.
• units ;

  magnetic moment ; ampere

  magnetic induction ; tesla or N/A -m

  magnetic field ; tesla
• magnetic declination ; the angle between the magnetic north and true north.
• the magnetic moment associated with a solenoid is given by the equation m = NiA.
• gauss law ; flux surrounding any body is equal to $1/ε0$times the charge enclosed by it.
• At Earth's pole, a compass needle will be show any particular direction in horizontal plane.
• phenomenon of working transformer ;

  The basic principle behind working of a transformer is the phenomenon of mutual induction between two windings linked by common magnetic flux.
• a step down transformer is used in a 6v bed lamp to convert 6v ac to 6v dc lamp.
• the no. of turns in the secondary coil divided by the no. of turns in the primary coil is called the transformer ratio.
• principle of production of electromagnetic waves ;

  If the charge is accelerated both the magnetic field and electric field will change with space and time, then electromagnetic waves are produced.
• The uses of the microwaves are similar to that of radio waves. They are used in communications, radio astronomy, remote sensing, radar, and of course, owing to their heating application, they are used in cooking as well.
• infrared waves are used in infrared photography, night vision, thermography etc.

  mosquitoes, snakes, vampire bats can detect infrared rays.
• if wavelength of electromagnetic radiation is doubled, energy of photon is halved.
• Microwaves have longer wavelengths and low frequencies. So they can be focussed along a straight line without much deviation and thus do not bend around corners of any obstacle coming in their path.

  so, they are used in radars.
• a beam of electrons emitted from a cathode plate in a high vacuum tube are called as cathode rays.
• work function ; it the minimum energy of incident radiation required to cause photo electric emission.
• photo electric effect ; when a beam of light strikes the surface of photosensitive materials, ejection of electrons take place. the ejected electrons are called as photons.
• millikan's experiment established an important fact that electric charge is quantised.
• de broglie's relation ;

  p = h/λ

  where p = momentum, h = plank's constant and λ = wavelength pf electron.