Create a circuit that includes a sensor, which in turn will enable me to measure the volume of liquid in a container by reading the voltage from a voltmeter.

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Planning

Aim:

The aim of this investigation is to create a circuit that includes a sensor, which in turn will enable me to measure the volume of liquid in a container by reading the voltage from a voltmeter.

Plan:

 1. I could use many methods to pick up a change in water level in a container. I could use a rotary potentiometer and attach it to a metal rod, then fix a cork to the metal rod, which will be used as the float that will rise with water level. I will need to use a potential divider in the circuit in order to pick up the changes in resistance, which will cause the voltage to rise or fall.

        2. I could also use a length of wire, which, as it becomes immersed in water causes changes in its conductance and therefore changes in its resistance and the voltage across the circuit.

        I am going to use a rotary potentiometer for my investigation. [No.1]

Apparatus:

        

        6v dry cell battery pack

        Voltmeter

        Rotary Potentiometer

        Wires

        Container for water

        Cork

        Copper Rod        

        Fixed Resistor

        Retort Stand

        Clamp & Boss

Preliminary Tests:

I carried out some preliminary tests with my apparatus in order to try and find the best setup for my main experiment. I tested how much water to use - because if I used under 600ml the cork wouldn't float.

        I examined whether to position the potentiometer so that the resistance rose when the water level rose or decreased when the water level rose, as this did not physically affect the experiment in any way, I decided it would look better to have the resistance fall as the water rose because this made the voltage increase and that is what I will be measuring.

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        The voltmeter could be connected either across the potentiometer or the fixed resistor. I tried both setups and discovered that more simple and readable readings where achieved by connecting the voltmeter across the fixed resistor.

        While performing the preliminary tests I discovered the potentiometer would not cause a change in resistance until the cork was lifted above roughly 35º from its starting position [Fig.1]. To solve this problem I positioned the potentiometer so that its starting position was now about 40º [Fig.2], this way even when the potentiometer was at rest it was causing less resistance in the circuit ...

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