Ohm’s Law The relationship between Voltage, Current and Resistance in any DC electrical circuit was firstly discovered by the German physicist Georg Ohm, ( ). 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 ( )

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 = W) or kilowatts (kW = 10 3 W). 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 = V 2 ÷ R] P (watts) = V 2 (volts) ÷ R (Ω) Also, [P = I 2 x R] P (watts) = I 2 (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)

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