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Alternating Current voltage time 0 maximum positive voltage (the peak voltage) maximum negative voltage (peak voltage) Direction of current and size constantly change. Mains frequency is 50 Hz

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Alternating Current 2 Voltage (V) Time (s) 0 peak voltage effective voltage The quoted value ( rms ) or Effective voltage of an a.c. supply is the same as the steady d.c. voltage which would produce the same heating effect in a resistance wire. The quoted value of the mains voltage in the UK is 230 V. The peak voltage is 325 V. Effective voltage is measured with a voltmeter. Peak voltage is measured with an oscilloscope.

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Alternating Current 3 The quoted value of an a.c. supply is also known as the r.m.s. value (root mean square). The peak value is 2 larger than this r.m.s. value. This applies to both voltage and current. Voltage Time peak value r.m.s value

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Alternating Current 4 Peak and r.m.s. values: Example The period of a sinusoidally varying current is 0.005 s. The peak value of the current is 4·0 A. Calculate a) the frequency b) the root mean square value of the current. Frequency = 1 / Period Frequency = 1 / 0.005 Frequency = 200 Hz

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Calculation of frequency timebase (s cm –1 ) y input 0.02 Find the time for one wave. This is the period. frequency = 1/period Example Time base = 0.02 s cm -1 Period = time base setting x no of boxes for 1 cycle Period = 0.002 x 4 = 0.08 s Frequency = 1 / period Frequency = 1 / 0.08 = 12.5 Hz.

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Direct Current D.C. stands for direct current. Batteries supply d.c. With d.c. the current is always in travelling in the same direction. The current flows.

Direct Current D.C. stands for direct current. Batteries supply d.c. With d.c. the current is always in travelling in the same direction. The current flows.

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