Presentation on theme: "Direct voltage and current 1. Alternating voltage and current 1 The alternating voltage may make an alternating current flow."— Presentation transcript:
Direct voltage and current 1
Alternating voltage and current 1 The alternating voltage may make an alternating current flow
Alternating voltage and current 2 1.The voltage changes direction as the coil is rotated. 2.In the UK there are 50 complete cycles in one second. 3.The frequency is 50Hz V t
Supply voltages - mains 1.UK Mains230V AC 50Hz 2.Europe230V AC 50Hz 3.USA110V AC60Hz
Direct voltage and current 2 1.Batteries produce a direct voltage. 2.Direct means one way 3.A direct voltage makes a direct current flow in a circuit V t
Oscilloscope This is a type of voltmeter that is used to show graphs of changing voltage.
Peak and RMS voltage 230V ___V
Adapting alternating voltage 1.Alternating can be converted to direct – this is called rectification – diodes are used for this. 2.Alternating voltage can be stepped up or stepped down – transformers are used for this.
Transformer – images 1
Transformer – images 3
Transformer – images 4
Transmitting electricity over long distances 1.When electricity passes through a cable heat is produced and energy is lost 2.To reduce the heat loss transformers are used 3.The heat loss depends on the current flowing 4.The current is stepped down before transmission using a transformer 5.In order to do his the voltage is stepped up 6.The power is not changed
The Transmission System
Transmission Towers These keep the cables away from the ground.
The National Grid
Epidemiological study Cases of leukemia Controls Exposed to fieldA=7C=46 not exposed to field B=27D=475 Calculate exposure ratios A/B and C/D Odds ratio =A/B divided by C/D