Unit 2 Lesson 1 GCSE circuit review Current Emf and pds Series and parallel circuits rules

What happens in an electrical circuit? Connect up a series circuit with a battery and 2 bulbs Use an ammeter and a voltmeter to provide evidence for how electricity behaves in a series circuit. Draw circuit diagrams, label your results. Come up with rules about V and I in series circuits. Present your findings on A3 paper. Repeat with parallel circuit. 15 minutes

Current in a series circuit If the current here is 2 amps… The current here will be… And the current here will be… In other words, the current in a series circuit is THE SAME at any point.

Current in a parallel circuit A PARALLEL circuit is one where the current has a “choice of routes” Here comes the current… And the rest will go down here… Half of the current will go down here (assuming the bulbs are the same)…

Current in a parallel circuit If the current here is 6 amps The current here will be… And the current here will be…

Kirchoff’s First Law 6A For example: If the current through here is 4A... …and the current through here is 2A… … then the current here will be 6A Gustav Kirchoff ( ) “The sum of the currents leaving a junction is the same as the sum of the currents entering that junction.” Law of Conservation of charge

Some example questions… 3A6A

Current Summary What is a current? What is d.c? What is a.c? What is conventional current? What is the equation for current? Current Unit? How is the ammeter placed in a circuit? Flow of charge Direct current. Alternating current. Current flowing from positive to negative I=∆Q/∆t amps (A) Series

Electromotive force and p.d. Components like batteries and power supplies provide a force that pushes the current around a circuit: we call this the “electromotive force” (e.m.f). Other components like bulbs and motors have work done to them by the current – the voltage across them is called the “potential difference” (p.d.) The sum of these EMFs… Is equal to the sum of the p.d.s Kirchoff’s Second Law

Voltage in a series circuit V VV If the emf across the battery is 6V… …and these bulbs are all identical… …what will the voltage across each bulb be? 2V

Voltage in a series circuit V V If the emf across the battery is 6V… …what will the voltage across two bulbs be? 4V

Voltage in a parallel circuit If the emf across the batteries is 4V… What is the voltage here? And here? VV 4V

Voltage What is p.d? Name some components that the charge has to do work on to pass through? What is the equation for voltage in symbols? What is the unit? What meter is used? How is it placed in a circuit? Electrical work done per unit charge = Work done/ charge V=W/Q volts (V) Voltmeter parallel

E.m.f. What components do work on charge? What is the full name given to this voltage measurement? Electromotive force. The cell /power supply applies a force to the charge carriers. It moves them around the circuit. It does work on the charge. What unit is e.m.f measured in? volts What is the equation? ε = W/Q

Conservation of energy in circuits. Explain how energy conservation occurs in an electrical circuit. Write an equation for energy conservation in a circuit. Circuit Σe.m.f. = ΣIR. This means the sums of the emf = sum of the voltages around a circuit as V=IR from Ohm’s Law

Summary In a SERIES circuit: Current is THE SAME at any point Voltage SPLITS UP over each component In a PARALLEL circuit: Current SPLITS UP down each “strand” Voltage is THE SAME across each”strand” Phet Ac and DC electroball

An example question: V1V1 V2V2 6V 3A A1A1 A2A2 V3V3 A3A3 Questions On Kirchoff More qns