```Ohm"s Law                                              Electromagnets
   It deals with the relationship between                An electromagnet is a type of magnet in
voltage and current in an ideal conductor.             which the magnetic field is produced by
   This relationship states that, the potential           an electric current. The magnetic field
difference (voltage) across an ideal                   disappears when the current is turned off.
conductor is proportional to the current              Electromagnets usually consist of a large
through it.                                            number of closely spaced turns of wire
   Ohm"s Law is given by:                                 that create the magnetic field.
V = I R , where V is the potential
difference between two points which                Electronics
include a resistance R. I is the current           It deals with electrical circuits that involve
flowing through the resistance. The                active electrical components such as vacuum
constant of proportionality is called the          tubes, transistors, diodes and integrated
"resistance", R.                                   circuits,      and       associated       passive
   For biological work, it is often preferable        interconnection technologies.
to use the conductance, g = 1/R ; in this
form Ohm"s Law is: I = g V                         Electrical resistance and conductance
Electric Field                                            Conductance (G) is a measure of how
well an artefact (such as an electrical
   Electric field is defined as the electric              component, not a material, such as iron)
force per unit charge (E = F/q)                        carries an electric current. It is measured
   The direction of the field is taken to be the          in Siemens (S).
direction of the force it would exert on a            Resistance (R) is a measure of how well
positive test charge.                                  an artefact resists an electric current. It is
   The electric field is radially outward from            measured in Ohms (Ω).
a positive charge and radially in toward a            The resistance (R) of an object is defined
negative point charge.                                 as the ratio of voltage across it (V) to
   Electric field intensity inside a charged              current through it (I), while the
hollow conductor, hollow conductor &                   conductance (G) is the inverse:
spherical surface is zero.
V       I       1
R     , G , G
Electric Potential                                               I      V      R
   It is the capacity of an electric field to do          1 S = 1 ohm -1
work on an electric charge, typically
measured in volts.                                 Measuring instrument
   It is the "push" of electricity through a          1. Ammeter : It is a measuring instrument
circuit.                                               used to measure the electric current in a
   The electric potential at infinity is                  circuit.
assumed to be zero.                                2. Voltmeter : It is an instrument used for
   Force and potential energy are directly                measuring electrical potential difference
related.                                               between two points in an electric circuit.
3. Galvanometer : It is an instrument used
to indicate the presence, direction, or
strength of a small electric current.
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