Ohm’s Law The relationship between Voltage, Current and Resistance in any DC electrical circuit...

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

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