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Ohm’s LawThe relationship between Voltage, Current and
Resistance in any DC electrical circuit was firstly
discovered by the German physicist Georg Ohm,
(1787 - 1854). Georg Ohm found that, at a constant
temperature, the electrical current flowing through a
fixed linear resistance is directly proportional to the
voltage applied across it, and also inversely proportional
to the resistance. This relationship between the Voltage,
Current and Resistance forms the bases of Ohms Law
Georg Simon Ohm(1789 - 1854)
Ohms Law Relationship
To find Voltage (V)
[V = I x R] V (volts) = I (amps) x R (Ω)
To find Current (I)
[I = V ÷ R] I (amps) = V (volts) ÷ R (Ω)
To find Resistance (R)
[R = V ÷ I] R (Ω) = V (volts) ÷ I (amps)
Ohms Law Triangle
Power in Electrical CircuitsElectrical Power, (P) in a circuit is the amount of
energy that is absorbed or produced within the circuit.
A source of energy such as a voltage will produce or
deliver power while the connected load absorbs it.
The quantity symbol for power is P and is the product
of voltage multiplied by the current with the unit of
measurement being the Watt (W) with prefixes used
to denote milliwatts (mW = 10-3W) or kilowatts (kW
= 103W). By using Ohm's law and substituting for V, I
and R the formula for electrical power can be found
as:
To find Power (P)
[P = V x I] P (watts) = V (volts) x I (amps)
Also,
[P = V2 ÷ R] P (watts) = V2 (volts) ÷ R (Ω)
Also,
[P = I2 x R] P (watts) = I2 (amps) x R (Ω)
The Power Triangle
One other point about Power, if the calculated power
is positive in value for any formula the component
absorbs the power, but if the calculated power is
negative in value the component produces power, in
other words it is a source of electrical energy.
Also, we now know that the unit of power is the
WATT but some electrical devices such as electric
motors have a power rating in Horsepower or hp.
The relationship between horsepower and watts is
given as: 1hp = 746W.
Ohms Law EquationsOhms Law Pie Chart
TYPES OF CIRCUITS
Series Circuit Parallel CircuitSeries-Parallel Circuit
SERIES CIRCUITS A Series Circuit has only one path to ground, so electrons
must go through each component to get back to ground. All
loads are placed in series.
Therefore:
1. An open in the circuit will disable the entire circuit.
2. The voltage divides (shared) between the loads.
3. The current flow is the same throughout the circuit.
4. The resistance of each load can be different.
PARALLEL CIRCUITS
A Parallel Circuit has multiple paths or branches to
ground. Therefore:
1. In the event of an open in the circuit in one of the
branches, current will continue to flow through the
remaining.
2. Each branch receives source voltage.
3. Current flow through each branch can be
different.
4. The resistance of each branch can be different.
SERIES-PARALLEL CIRCUITSA series-parallel circuit has some components in
series and others in parallel. The power source and
control or protection devices are usually in series; the
loads are usually in parallel.
The same current flows in the series portion, different
currents in the parallel portion. The same voltage is
applied to parallel devices, different voltages to series
devices. If the series portion is broken, current stops
flowing in the entire circuit. If a parallel
Problems on the Ohm's LawProblem: A potential difference of 10 V is applied across
a conductor whose resistance is 25Ω. The current in the
conductor is ? (Answer =.40 Amperes)
Problem: If the current passing through conductor is
5A,and conductance of the conductor is 50 ohm.Calculate
the potential applied across the conductor ? (Hint:
Conductance=1/Resistance, Answer=0.1 volts ).
Problem: Five cells each of internal resistance
0.2Ω and e.m.f. of 2V are connected in series with
a resistance of 4Ω.The current through the
external resistance is ?(Answer: 2 Amperes).
Problem: Two resistance when connected in
parallel have equivalent resistance of 3Ω. When
one of the resistance is burnt and broken, the net
resistance is 12 Ω. What is the resistance of burnt
resistor. (Answer: 4Ω)
Reference:
http://www.autoshop101.com/trainmodules/elec_circuits/circ130.html
http://www.electronics-tutorials.ws/dccircuits/dcp_2.html
The End
… Thank you …