Transcript Ohm`s Law - UStudy.in

Ohm’s Law
 The 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 Circuits
 Electrical 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 = 103W)
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 = V2 ÷ R]
 [P = I2 x R]
P (watts) = V (volts) x I (amps) Also,
P (watts) = V2 (volts) ÷ R (Ω) Also,
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 Equations
Ohms Law Pie Chart
TYPES OF CIRCUITS
 Series Circuit
 Parallel Circuit
 Series-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 CIRCUITS
 A 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 Law
 Problem: 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_circu
its/circ130.html
 http://www.electronicstutorials.ws/dccircuits/dcp_2.html
The End
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