Hello, Im Jason Fernandes, 18, and a student at college in london. Basically i have to complete a planning exercise for my physics exam practical paper, I was given this task, I will post the details below:
'A student is comparing materials for use as electrical insulation. The student decided to measure the resisticity of a number of different materials. The circuit below is used to determine the resistance of the sample
-Diagram of a circuit, 3v d.c power supply connected in series to a milliammeter, and then to a sampler of insulating matetial. A voltmeter is connected across the insulator.
The student finds that the milliammeter give a small reading. However when the voltmeter is removed from the circuit the milliameter reads zero. The student concludes that the current registered on the milliammeter is due to the voltmeter and not the insulating material. The student decides to make several modifivcations to the experiment in order to obtain a measurable current in the insulating material.
Design a lab experiment to measure the resistuvty on an insulating material such as paper, PVC, Glass. You may asume that standard colelge equipment is avaiblable.
yoour answer should contain details of the following:
a) The steps which would be taken to ensure the current measured is not due to the current passing through the voltmeter.
b) The modifications you would make to circuit in order to obtain a measurable current.
c) What size and dimensions of insulating material you would use and reasons for ur choice.
d) how the resistivity would be found and measured
e) safety precautions.
f) any design featured that would improve the accuracy of ur results.'
and thats it. It might look complicated, but dont worry im not looking for someone to write it out for me. We have to go sit in a hall one morning and write the whole thing up from scratch to make sure we understand it.
I just need help in overcoming 1 problem, the current going through the voltmeter:
Treating the voltmeter (digital, typical resistance of 1M ohm supposedly)
like a resistor it takes up a large proportion of the current because the resistance of a sample that im supposed to be measuring is pretty high. For my test values, i used a glass block of resistivity in the region of 10^12 Ohm m^-1, being 0.003m in length, and 0.01m^2 in cross sectional area. using the equation R = pl/A , got a resistance of 3 x 1-611 ohms.
any suggestions on what to do? I dont think Im supposed to make the resistance of the insulator sample comparintively smaller that the resistance of the voltmeter. I think the solution lies in the circuit. I thought about increasing the voltmeter resistance somehow, or something else.
The goal is to acheive current in the insulator of no small than 10^-12 amps, using a high tension supply supply.
Most other problems i have covered, but any other help would be great.
If u can help me, could u please email me too, I would appreciate it.
thanks, Jason Fernandes
'A student is comparing materials for use as electrical insulation. The student decided to measure the resisticity of a number of different materials. The circuit below is used to determine the resistance of the sample
-Diagram of a circuit, 3v d.c power supply connected in series to a milliammeter, and then to a sampler of insulating matetial. A voltmeter is connected across the insulator.
The student finds that the milliammeter give a small reading. However when the voltmeter is removed from the circuit the milliameter reads zero. The student concludes that the current registered on the milliammeter is due to the voltmeter and not the insulating material. The student decides to make several modifivcations to the experiment in order to obtain a measurable current in the insulating material.
Design a lab experiment to measure the resistuvty on an insulating material such as paper, PVC, Glass. You may asume that standard colelge equipment is avaiblable.
yoour answer should contain details of the following:
a) The steps which would be taken to ensure the current measured is not due to the current passing through the voltmeter.
b) The modifications you would make to circuit in order to obtain a measurable current.
c) What size and dimensions of insulating material you would use and reasons for ur choice.
d) how the resistivity would be found and measured
e) safety precautions.
f) any design featured that would improve the accuracy of ur results.'
and thats it. It might look complicated, but dont worry im not looking for someone to write it out for me. We have to go sit in a hall one morning and write the whole thing up from scratch to make sure we understand it.
I just need help in overcoming 1 problem, the current going through the voltmeter:
Treating the voltmeter (digital, typical resistance of 1M ohm supposedly)
like a resistor it takes up a large proportion of the current because the resistance of a sample that im supposed to be measuring is pretty high. For my test values, i used a glass block of resistivity in the region of 10^12 Ohm m^-1, being 0.003m in length, and 0.01m^2 in cross sectional area. using the equation R = pl/A , got a resistance of 3 x 1-611 ohms.
any suggestions on what to do? I dont think Im supposed to make the resistance of the insulator sample comparintively smaller that the resistance of the voltmeter. I think the solution lies in the circuit. I thought about increasing the voltmeter resistance somehow, or something else.
The goal is to acheive current in the insulator of no small than 10^-12 amps, using a high tension supply supply.
Most other problems i have covered, but any other help would be great.
If u can help me, could u please email me too, I would appreciate it.
thanks, Jason Fernandes