5.2.2 D.C. Circuits Practical circuits Electromotive force and internal resistance Kirchhoff’s laws Series and parallel arrangements Potential divider

Practical circuits

Electromotive Force and Internal Resistance Emf - is the amount of energy of any form that is changed into electrical energy per coulomb of charge. Measured in volts. Batteries get hot after long periods of use because some of the current moving through them gets turned into heat energy by the battery’s internal resistance.

1.At any junction in a circuit, the sum of the currents arriving at the junction = the sum of the currents leaving the junction. 2.In any loop (path) around a circuit, the sum of the emfs = the sum of the pds. Kirchhoff’s laws I1I1 I 1 =I 2 +I 3 +I 4 I4I4 I3I3 I2I2 Energy in = Energy out emf = pd 1 + pd 2 + pd 3 + pd 4 pd2 pd1 pd4 pd3 Cell

Components in series are connected together in a chain looped round. Eg: Components in parallel are connected like Series and parallel arrangements A V

Potential divider the larger the resistor, the greater the voltage needed across it for the same current to flow through it.

5.2.1 Electric Current Electric current Potential difference Ohm’s law Resistance and resistivity Electrical energy and power

Electric Current Current electricity is about moving charged particles. If you allow the charge that builds up in static electricity to flow, you get a current. Current is the rate of flow of charge; it is the amount of charge flowing per second through a conductor. The equation for calculating current is: I=Q t

Potential difference Potential Difference (pd) - is the amount of electrical energy that is changed into other forms of energy per coulomb of charge.

Ohm’s law Ohm’s law states that if it takes 1 volt (1 joule per coulomb) to drive a current of 1 amp through a resistor, it has a resistance of 1 ohm.

Resistance and resistivity The more resistance there is the more energy that is needed to push the same number of electrons through part of the circuit. Resistance is measured in ohms, , and the resistance of a component can be found using an ohmmeter.

Electrical energy and power Work Done (or Energy) and Power Equations The definition of voltage tells us that: W = VQ The definition of current tells us that, Q = It W = V I t Of course, we already know that: Power = V I