1Everything Science www.everythingscience.co.za11. Electric circuitsPhysicsGrade 11
2Everything Science www.everythingscience.co.zaOhms LawOhm’s Law states that the amount of current through a conductor, at constant temperature, isproportional to the voltage across the resistor. Mathematically we writewhere I is the current through the conductor, V is the voltage across the conductor and R isthe resistance of the conductor.I=VR
3Everything Science www.everythingscience.co.zaOhms Law and conductorsConductors that obey Ohm’s Law are called ohmic conductors; those that do not are callednon-ohmic conductors.
4Everything Science www.everythingscience.co.zaSeries and parallel circuitsThe equivalent resistance ofresistors in parallel (Rp) can becalculated as follows:The equivalent resistance ofresistors in series (Rs) can becalculated as follows:Rs=R1+R2+R3+... 1Rp=1R1+1R2+1R3+...
5Everything Science www.everythingscience.co.zaMore on series and parallel circuitsIT=I1=I2=I3 VT =V 1+V2+V3In a series circuit the amount of current is thesame through any component in the circuit.And the total voltage of the circuit has to beequal to the sum of the voltages over allthree resistors. This can be expressed as(assuming three resistors):In a parallel circuit the voltage is equalacross all components in the circuit. And allthe currents through each resistor must addup to the total current in the circuit. This canbe expressed as (assuming three resistors):VT =V 1=V 2=V 3 IT =I1+I2+I3
6Everything Science www.everythingscience.co.zaElectrical power and energyElectrical power is the rate at which electrical energy is converted in an electric circuit.Power (P) is measured in watts (W).Using Ohms Law we can find two alternate forms of this expression to calculate power:The electrical energy dissipated is and is measured in joules (J).P=I⋅VP=I2⋅R P=V 2RE=P⋅t
7Everything Science www.everythingscience.co.zaFor more practice see:www.everythingscience.co.zaShortcode: ESBQH