Download 5.2.2 DC Circuits

5.2.2 D.C. Circuits
Practical circuits
Electromotive force and internal resistance
Kirchhoff’s laws
Series and parallel arrangements
Potential divider
Practical circuits
Electromotive Force and
Internal Resistance
Emf - is the amount of energy of any
form that is changed into electrical
energy per coulomb of charge.
Measured in volts.
Batteries get hot after long periods of
use because some of the current
moving through them gets turned into
heat energy by the battery’s internal
resistance.
Kirchhoff’s laws
1.
At any junction in a circuit, the sum of the currents arriving at the
junction = the sum of the currents leaving the junction.
I2
I1
I3
I1=I2+I3+I4
I4
2.
In any loop (path) around a circuit, the sum of the emfs = the sum
of the pds.
pd1
Energy in = Energy out
Cell
emf = pd1 + pd2 + pd3 +
pd4
pd2
pd3
pd4
Series and parallel
arrangements
Components in series are connected
together in a chain looped round. Eg:
A
Components in parallel are connected
like
V
Potential divider
the larger the resistor, the greater
the voltage needed across it for
the same current to flow through
it.
5.2.1 Electric Current
Electric current
Potential difference
Ohm’s law
Resistance and resistivity
Electrical energy and power
Electric Current
Current electricity is about moving
charged particles. If you allow the charge
that builds up in static electricity to flow, you
get a current.
Current is the rate of flow of charge; it is
the amount of charge flowing per second
through a conductor.
The equation for calculating current is:
I=Q
t
Potential difference
Potential Difference (pd) - is
the amount of electrical energy
that is changed into other forms of
energy per coulomb of charge.
Ohm’s law
Ohm’s law states that if it takes 1 volt
(1 joule per coulomb) to drive a
current of 1 amp through a
resistor, it has a resistance of 1
ohm.
Resistance and resistivity
The more resistance there is the more
energy that is needed to push the same
number of electrons through part of the
circuit.
Resistance is measured in ohms, W,
and the resistance of a component can
be found using an ohmmeter.
Electrical energy and power
Work Done (or Energy) and Power Equations
The definition of voltage tells us that:
W = VQ
The definition of current tells us that, Q = It
W=VIt
Of course, we already know that:
Power = V I