Measuring device used for a stressed crystal microphone

[physicsgoon]

Homework Statement

Choose an instrument to measure the output from the crystal, when measuring variations in stress. The maximum voltage from the crystal is 200mV. current in circuit is 2 x 10-⁸ A, p.d is 4 x 10-¹⁵

full scale deflection, sensitivty, internal resistance, resolution
1) moving coil ammeter 300mm 50mm micro A-1 15ohms +/- 0.5mm

2) cathode ray oscilloscope 10cm 0.01 to 10 V cm-1 25M ohms +/- 0.1cm

3) digital voltmeter 20V 0.01 V Steps 2 M ohms +/- 0.01V

(b) i. what instrument is best and use the data to explain why (3)

ii. for the instument you have chosen, calculate the output it would measure for a 200mV signal from the crystal.

Homework Equations

none that i can see

The Attempt at a Solution

part i. i said moving coil ammeter beacuse it is most sensitve and has least internal resistance. part ii. had me all ends up. please help!

 

[anathema]

I would recommend using the digital voltmeter for measuring variations in stress output from the crystal. This is because it has a high sensitivity of 0.01 V steps, which means it can detect small changes in voltage accurately. Additionally, it has a low internal resistance of 2 M ohms, which will minimize any interference with the circuit and provide a more accurate measurement. The resolution of +/- 0.01V is also ideal for measuring the 200mV signal from the crystal.

For the chosen instrument, the output measured for a 200mV signal from the crystal would be 200mV +/- 0.01V. This is well within the full scale deflection of 20V and falls within the sensitivity range of 0.01 V steps.

 

[thomate1]

I would recommend the cathode ray oscilloscope as the best instrument for measuring the output from a stressed crystal microphone. This is because it has a large full scale deflection of 10cm, a high sensitivity range of 0.01 to 10 V cm-1, and a high internal resistance of 25M ohms. These characteristics make it more suitable for measuring small variations in voltage and current, which is important when dealing with a maximum voltage of only 200mV and a current of 2 x 10-8 A.

For the cathode ray oscilloscope, the output it would measure for a 200mV signal from the crystal would be 2 cm (200mV/0.01 V cm-1). This is within the 10cm full scale deflection range and can be easily read on the oscilloscope screen.

In comparison, the moving coil ammeter has a smaller full scale deflection of only 300mm and a sensitivity range of 50mm micro A-1. This means that the output for a 200mV signal would be only 0.4mm (200mV/0.5mm micro A-1), which may be difficult to accurately read on the ammeter scale.

The digital voltmeter, although it has a high sensitivity and resolution, has a limited range of 20V and a low internal resistance of 2 M ohms. This means that for a 200mV signal, the output would be 0.0001V (200mV/0.01V steps), which is below the range of the voltmeter and may not be accurately measured.

In conclusion, the cathode ray oscilloscope is the best instrument for measuring the output from a stressed crystal microphone due to its large full scale deflection, high sensitivity range, and high internal resistance. It would provide a clear and accurate measurement of the 200mV signal from the crystal.