IGCSE›Oxford AQA IGCSE Physics›Mind mapsElectricity Transmission & DistributionOxford AQA IGCSE Physics: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsThe GridNetwork of transmission cables and transformersStep-up transformer raises voltage for transmissionStep-down transformer lowers it before homesWhy high voltage?High voltage means lower current for the same powerLower current means less heating in cablesLess energy wasted, so more efficientInside a transformerPrimary and secondary coils on a soft iron coreAlternating current makes a changing magnetic fieldThat field induces a pd in the secondary coilWorks with ac onlyNational GridtransformersVpV_pVpVsV_sVsnnnStep-up and step-downStep-up: more turns on the secondaryStep-down: fewer turns on the secondarySwitch mode transformers are small, light, high frequencyEquationsVpVs=npns\frac{V_p}{V_s} = \frac{n_p}{n_s}VsVp=nsnpIdeal transformer: VpIp=VsIsV_p I_p = V_s I_sVpIp=VsIs230 V, 100 to 1000 turns gives 2300 VExam tipsState that transformers need ac, not dcChain: higher voltage, lower current, less heating