* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Alternating Current - The Place Programme
Ground (electricity) wikipedia , lookup
Variable-frequency drive wikipedia , lookup
History of electromagnetic theory wikipedia , lookup
Power inverter wikipedia , lookup
Electric machine wikipedia , lookup
Opto-isolator wikipedia , lookup
Electric power system wikipedia , lookup
Pulse-width modulation wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Skin effect wikipedia , lookup
War of the currents wikipedia , lookup
Power engineering wikipedia , lookup
Current source wikipedia , lookup
Voltage optimisation wikipedia , lookup
Utility frequency wikipedia , lookup
Stray voltage wikipedia , lookup
Power electronics wikipedia , lookup
Three-phase electric power wikipedia , lookup
Mercury-arc valve wikipedia , lookup
Electrical ballast wikipedia , lookup
Buck converter wikipedia , lookup
Electrification wikipedia , lookup
Switched-mode power supply wikipedia , lookup
History of electric power transmission wikipedia , lookup
Earthing system wikipedia , lookup
Alternating Current Learning Outcomes • Distinguish between alternating and direct current. • State the frequency of UK mains electricity. • Describe how the potential of the live wires varies each cycle. • State that the potential of the neutral wire is approximately zero. • Use oscilloscope traces to compare direct and alternating potential differences. Starter Draw and label a waveform with the following labels: •Amplitude •Wavelength •Peak •Trough •Also, define frequency Starter Wavelength Peak Trough Draw and label a waveform with the following labels: •Amplitude Amplitude •Wavelength •Peak •Trough •Also, define frequency = number of waves passing a fixed point every second (Hz) A.C. D.C. – not the band!! • Direct current and alternating current are different types of electric current • You should know the differences between direct current (d.c.) and alternating current (a.c.) electrical supplies. Direct Current • If the current flows in only one direction it is called direct current, or d.c. • Batteries and cells supply d.c. electricity, with a typical battery supplying maybe 1.5V. • The diagram shows an oscilloscope screen displaying the signal from a d.c. supply. We can’t see current but we can put it In to an image using a oscilloscope. Alternating Current • If the current constantly changes direction, it is called alternating current, or a.c.. • Mains electricity is an a.c. supply, with the UK mains supply being about 230V. • It has a frequency of 50Hz (50 hertz), which means it changes direction, and back again, 50 times a second. • The diagram shows an oscilloscope screen displaying the signal from an a.c. supply. Why does the graph go positive and negative? Match em’ up • Match the subject with the type of current a.c. or d.c. • • • • • • Torch Lamp in the living room Bicycle lamp Power shower Mobile phone Mobile phone charger Match em’ up • Match the subject with the type of current a.c. or d.c. • Torch – d.c. • Lamp in the living room – a.c. • Bicycle lamp – d.c. • Power shower a.c. • Mobile phone d.c. • Mobile phone charger a.c. Power pack • Why on a power pack does the a.c. supply have yellow plastic circles around the points whereas d.c. have red and black? – What do the red and black represent? D.C. A.C. Power pack • Why on a power pack does the a.c. supply have yellow plastic circles around the points whereas d.c. have red and black? – What do the red and black represent? – Red = positive + – Black = negative – – It flows from negative to positive DEMO • Will a bulb light in a.c. and d.c.? • In a direct current the electrons are travelling all around the circuit. In a a.c. current they oscillate only a few centimetres in each direction – they pass energy on through energy transfer. Mains Electricity • Main circuits have live and neutral wire. • Mains has an a.c. supply and is very dangerous as it repeatedly changes form + to – and reaches over 300V both ways. – If we were to look at this on an oscilloscope what would happen if we increased the potential difference (voltage) – it should make the waves taller. – What happens if we increase the frequency – it increases the number of waves/sec so it makes them more squashed on the screen HIGHER!! • The potential difference of the live terminal varies between a large positive value and a large negative value. • However, the neutral terminal is at a potential difference close to earth, which is zero. • The diagram shows an oscilloscope screen displaying the signals from the mains supply. – The red trace is the live terminal and the blue trace the neutral terminal. – Note that, although the mean voltage of the mains supply is about 230V, the peak voltage is higher. Oscilloscope Traces • There are two things that you need to know about on the oscilloscope – the time base – the Y-gain • The time base allows us to look at how long a wavelength takes. We can alter the setting of the time-base on the oscilloscope so e.g. 10 milliseconds per centimetre shows that each cm on the screen is a time interval of 10s • The Y-gain can also be set e.g if it is set at 0.5V/cm the it means that each cm of height is due to 0.5 V. • Confused???? Alternating current Problems! • Q: An a.c. source is connected to an oscilloscope. The waveform of the alternating potential difference from the source is displayed on the oscilloscope screen as below. • The Y-gain setting of the oscilloscope is 0.5 V/cm. Determine the amplitude of the alternating potential difference. Practical • Use the oscilloscopes and make notes on what happens when you alter the time base setting and the Y gain. • You need to be able to read information off oscilloscopes about frequency. Plenary • Draw an oscilloscope trace in your book and give set y-gains and time bases and set a question for your partner. Learning Outcomes • Distinguish between alternating and direct current. • State the frequency of UK mains electricity. • Describe how the potential of the live wires varies each cycle. • State that the potential of the neutral wire is approximately zero. • Use oscilloscope traces to compare direct and alternating potential differences.