- Physics
- Ready-made model
- Class 10 to 12
Rectifier Using DC Using Volt Meter Physics Working Model Educational Investigatory Project
Code B0C3H5XBQK
- Paid for and delivered by Amazon. The current price and the delivery date for your PIN code are shown there.
- Sold by Gurukul Technicals Institute, Delhi.
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In this project guide
Ready-made model
About this model
This investigatory model demonstrates a rectifier, a circuit that converts alternating current (AC) into direct current (DC), using a voltmeter to measure the DC output. It is a practical way to study how diodes let current flow in only one direction.
How it works
The science behind it
The idea the model demonstrates, in words you can use in your report and when you explain it.
A p-n junction diode conducts when forward biased (p side more positive) and blocks current when reverse biased; a silicon diode needs about 0.7 V to start conducting. Indian mains AC is 230 V at 50 Hz, meaning 50 complete cycles per second. In a half-wave rectifier, one diode passes only the positive half-cycles, so the output is one-way pulses with gaps between them. A full-wave rectifier, using two diodes with a centre-tapped transformer or four diodes in a bridge, uses both halves, so its output pulses come at twice the input frequency, 100 Hz for a 50 Hz supply. This output is DC but pulsating. A filter capacitor across the output, where one is fitted, charges at each peak and supplies current in between, smoothing it into steadier DC. The peak of an AC voltage is √2 times its rms value, so a 12 V rms supply peaks at about 17 V.
Make it yourself
Make a half wave and full wave rectifier with a DC voltmeter yourself
Build your own version from scratch, or use the steps to understand how the ready-made model is put together before you present it.
What you need 9
Step by step 9 steps
Test every diode on the multimeter's diode range: about 0.5 to 0.7 V one way and no reading the other way.
- Build the half wave circuit
One diode from the first AC input terminal to a 'half wave positive' point, band towards that point. The second AC input terminal is its negative.
- Build the bridge beside it
The two diodes whose bands meet form the positive output, the two whose plain ends meet form the negative output, and the other two corners go to the AC input terminals.
Make one output section with the load resistor, the LED and its resistor, and the analogue voltmeter (its + terminal to the positive side), and wire the DPDT switch so this section is fed by either the half wave or the full wave outputs, both positive and negative.
Fit the capacitor through its own switch across the output section, long leg to positive, and leave it switched out for now.
With the adapter unplugged, connect it to the AC input terminals. An adult then plugs it in. Read the AC input on the multimeter's AC range.
Select half wave and read the analogue meter, then select full wave: the reading should roughly double. Compare both with the ideal values of 0.45 and 0.9 times the AC reading, less the drop across the diodes.
- Switch in the capacitor
The reading rises towards the peak value, about 1.4 times the AC reading less the diode drops, because the capacitor fills the gaps between pulses.
Ask the adult to switch off, connect the analogue voltmeter straight across the AC input, and switch on: the needle only trembles near zero, because the average of AC over a cycle is zero. Switch off and wait a minute for the capacitor to discharge before touching the board.
Read this first
Safety first
Go through these points before you build or switch anything on. Younger students should do this with an adult.
- Use only a low-voltage AC adapter, plugged in and switched off by an adult; students must never connect anything to a 230 V socket or open the adapter.
- Fit the electrolytic capacitor with its long leg to the positive output, and use one rated 25 V or more.
- Ask the adult to unplug the adapter before you change any connection, and let the capacitor discharge first.
- Use the soldering iron only with an adult and rest it in its stand.
Troubleshooting
If something does not work
The usual problems with this model and how to fix them. Open a problem to see the fix.
The analogue needle tries to move backwards
The meter is connected the wrong way round, or the half wave diode is reversed. Swap the meter leads, or check that the diode's band faces the positive output.
The full wave reading is no higher than the half wave reading
One bridge diode is open or wired wrongly, so the bridge is only passing one half of each cycle. Unplug the adapter and test each diode again.
The adapter gets warm or the output reads zero
A reversed diode in the bridge may be shorting the adapter. Ask the adult to unplug it at once, then check that the bands meet only at the positive corner.
The readings are higher than the label suggests
Simple AC adapters often give more than their marked voltage when lightly loaded. Measure the real AC input and use that figure in your calculations.
Exhibition day
How to present it
A running order for the exhibition table or the practical, step by step.
Draw the input AC wave and the rectified output wave side by side on a chart.
Note the voltmeter reading and explain why it shows DC.
Explain the difference between half-wave and full-wave rectification.
If the model works from the mains, ask a teacher to plug it in and keep your hands off the terminals while it is on.
Practice
Viva questions
Practice questions on this model, with short answers. Try each one aloud before you open the answer.
What is rectification?
The conversion of alternating current into direct current.
Why can a diode be used as a rectifier?
It conducts only when forward biased, so it allows current to flow in one direction only.
What is the output frequency of a full-wave rectifier on a 50 Hz supply?
100 Hz, because both halves of each input cycle produce an output pulse.
What is the purpose of the filter capacitor?
It smooths the pulsating DC output by charging at each peak and discharging between peaks.
Project file
Project file outline
The headings of the project file, in order. Give each heading its own section and write it in your own words.
Free ebook: Writing a Science Project FileContents
- Aim: to convert AC into DC with half wave and full wave rectifiers and measure the output
- Introduction: why electronic devices need DC
- The p-n junction diode in forward and reverse bias
- Working of the half wave and bridge rectifiers, with waveform sketches
- Average value of the rectified output: 0.45 and 0.9 times the AC reading
- Observations: AC input, half wave and full wave DC readings, with and without the capacitor
- Why a DC voltmeter reads zero on AC
- Precautions: a low-voltage adapter only, connected by an adult, and never mains wiring
- Conclusion and bibliography
Buying checklist
Before you buy
What to check before you order the model, and what to do when it arrives.
1Before you order
- Check that rectifiers are part of your syllabus and whether your teacher wants half wave, full wave or both.
- Read the listing to see how the model is powered and what meter it uses, and make sure an adult handles any plug.
- Practise explaining why the full wave output is about twice the half wave output.
- Keep the box so the meter is protected in transport.
- Check the delivery date for your PIN code on the marketplace, and order well before the exhibition or practical.
2When it arrives
- Test it with an adult as soon as it arrives, and note the readings so you know what is normal.
Next steps
Take it further
Ways to turn this model into a bigger investigation or a stronger exhibition entry.
Measure the ripple with the multimeter's AC range across the output, with and without the capacitor, and compare capacitor values.
Add a 5 V voltage regulator after the capacitor and show a steady output that hardly changes with load.
Plot output voltage against load resistance, with and without the capacitor, and explain the fall in terms of ripple.
Audience
Who it suits
Class 12 physics students preparing an investigatory project on semiconductor diodes and rectifiers.
- ClassClass 10 to 12
- SubjectPhysics
- TypeReady-made model
Free to read
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