I intend to study a circuit, in which I will determine the electro motive force (emf) and total internal resistance (tir) of a power supply.

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Hannah Proctor 3PAW

Practical assessment – Power supply.

Aim:

        I intend to study a circuit, in which I will determine the electro motive force (emf) and total internal resistance (tir) of a power supply.

Diagram:

        E = emf, r = tir, R = potentiometer, V = voltmeter, A = ammeter.

Results of preliminary trials:

        I did some preliminary testing to determine the range over which the variables will change, here are the results…

                

… From my preliminary tests I found that a decrease of 1A results in an increase of 0.16V on average. Thus I have decided that a decrease of 0.5A for each reading should give me enough information to calculate the emf and tir if I were to take seven readings.

Method:

        I will set up my equipment as shown and as I vary the current on the potentiometer, and read the voltage from the digital voltmeter (accurate to 100th of a volt) I have chosen to use this degree of accuracy because my preliminary tests show accuracy to 2 decimal place will be most appropriate. I will vary A in steps of 0.5A and thus I will start at 10A, 9.5A, 9A etc until 7A

        I will measure the current on an analogue meter accurate to 100th of an amp. I have chosen to work with this degree of accuracy because my preliminary trials dictated that would be the most appropriate and accurate.

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        To ensure a fair test I will try to keep the temperature constant in the circuit and in the room, also the equipment to be used and the degree of accuracy to which I will measure will be kept constant. However I do realise that I cannot control the temperature but ideally that is what I would like to do.

        I should be able to measure the voltage to (+/- 0.05) +2% volts plus five per cent of the answer which is one hundredth of a volt plus five per cent due to the error in the machine ...

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