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Lost Volts
Lost Volts (Product Code: SLE/EAM/19) is a self-contained apparatus for finding the EMF and internal resistance of a cell by experiment. Seven appropriately rated resistors and a push switch are housed in one unit, so students connect a single source, a voltmeter and an ammeter instead of wiring up a row of loose resistors. It is made by Jain Scientific Equipments Pvt Ltd (ScienceLab), Ambala, India, for school and college laboratories that want a quicker, tidier version of this classic piece of physics practical equipment for CBSE and similar syllabuses.
Specifications
| Parameter | Detail |
|---|---|
| Purpose | Experimental determination of the EMF and internal resistance of a cell |
| Load resistors | Seven appropriately rated resistors housed in the unit |
| Switch | Push switch, reducing unnecessary battery drain and excessive heat in the resistors |
| Source required | 6V DC source of EMF |
| Meters required | One voltmeter and one ammeter |
| Design advantage | Removes the complications of wiring separate resistors |
Typical Use
The name comes from the idea behind the experiment: when a cell drives current through a load, part of its EMF is “lost” across its own internal resistance, so the terminal voltage falls as the current rises. With the 6V DC source connected, the ammeter placed in series and the voltmeter across the source terminals, students press the push switch and record a voltage and current pair with each built-in resistor in circuit. Plotting terminal voltage against current gives a straight line whose intercept on the voltage axis is the EMF and whose gradient gives the internal resistance.
Because the switch only passes current while it is held down, the cell is not left discharging between readings and the resistors do not warm up, which keeps successive readings consistent through a practical period. It is a useful addition to any school physics lab equipment in India where the internal-resistance practical is run by several groups at once. Tip: take each reading promptly after pressing the switch, then release it before changing the load.
Manufacturer
Lost Volts is built by Jain Scientific Equipments Private Limited, a company in Ambala, Haryana that sells its teaching apparatus under the ScienceLab name to schools, colleges and distributors. More about the business and its electricity and magnetism range is on our company profile page.
Related Electricity and Magnetism Equipment
Items that complete the internal-resistance set-up on the bench:
- Digital Voltmeter — reads the terminal potential difference of the source at each load setting
- Digital Ammeter — records the current drawn from the source for the voltage–current graph
- Battery Holder, C — holds cells to build up the source whose internal resistance is being measured
- Stackable Leads — connecting leads for linking the source, meters and unit
- Apparatus for Studying f.e.m. and Internal Battery and Battery Resistance — an alternative apparatus for the same EMF and internal-resistance practical
Browse the complete Electricity and Magnetism range for more circuit and field apparatus.
Frequently Asked Questions
What else do I need to run the experiment?
A 6V DC source of EMF, a voltmeter and an ammeter, plus connecting leads. These are connected to the unit rather than built into it; suitable meters and leads are listed above.
How many load resistors does the unit contain?
Seven, each appropriately rated for the purpose. Individual resistance values are not listed in our current product documentation, so please contact us if your worksheet needs them in advance.
Why is a push switch fitted instead of a toggle switch?
Current flows only while the switch is pressed. This reduces unnecessary drain on the battery and stops excessive heat building up in the resistors between readings.
Can I use a bench power supply as the source?
The unit is intended for a 6V DC source of EMF. A cell or battery is the usual choice, because the aim is to measure that source’s own internal resistance; a well-regulated supply shows very little “lost volts” and gives a less instructive result.
What should an institutional quotation request include?
The product code SLE/EAM/19, the number of units, whether you also need meters, leads or cell holders, and the delivery address. Send these through our contact page.
Is bulk or export supply possible?
Yes. ScienceLab supplies schools, colleges, tender buyers and distributors in India and international markets; quantities and dispatch details are confirmed with each quotation.
Request a Quote
To order Lost Volts for your laboratory, send your requirement through our contact page or add the item to the enquiry cart together with any meters and leads you need, and our team will reply with a quotation.
Last updated: 24 September 2026
