Test question

[dbabn7]

Good Morning:
I was wondering if someone could help me understand the following question Thank you:
Insulation resistance tests are best made with a direct-reading Megger. These tests can
also be made with a high-resistance voltmeter and a source of d.c. supply. Assume that a direct reading instrument is not available but you have on hand a 100-volt voltmeter having a sensitivity of 5000 ohms per volt and a 100-volt battery. The battery is connected in series with the voltmeter. One free battery lead is connected to the wire whose insulation resistance is to be measured, and the other free lead to the grounded circuit. With this hookup, the volt meter
reads 50 volts.
22. The insulation resistance, in ohms, of the above conductor is
A. 500 B. 5,000
C. 250,000
D. 500,000
23. The resistance, in ohms, of the above-mentioned voltmeter is
A. 500 B. 5,000
C. 250,000
D. 500,000

 

[synchro]

A voltmeter with a 5000 ohms per volt sensitivity will have an input resistance of 5000 Ω/V x 100V = 500,000 ohms when set to a 100V full scale.
The insulation resistance and the input resistance of the voltmeter are placed in series with the battery, and form a voltage divider off of the 100 volt battery voltage. To get the 50V reading the voltage divider ratio will be 1/2, and so the insulation resistance must be equal to the input resistance of the voltmeter, or 500,000 ohms. So the answer to 22. is D., and the answer to 23. is also D.

 

[dbabn7]

Thank you so much for your help.

 

[GoldDigger]

Just for your future information, when a question is posted that looks like homework, we prefer that you at least attemtp to start solving the problem, We will then guiide youi to the correct solution and you will learn more in the process.

 

[garbo]

Good Morning:
I was wondering if someone could help me understand the following question Thank you:
Insulation resistance tests are best made with a direct-reading Megger. These tests can
also be made with a high-resistance voltmeter and a source of d.c. supply. Assume that a direct reading instrument is not available but you have on hand a 100-volt voltmeter having a sensitivity of 5000 ohms per volt and a 100-volt battery. The battery is connected in series with the voltmeter. One free battery lead is connected to the wire whose insulation resistance is to be measured, and the other free lead to the grounded circuit. With this hookup, the volt meter
reads 50 volts.
22. The insulation resistance, in ohms, of the above conductor is
A. 500 B. 5,000
C. 250,000
D. 500,000
23. The resistance, in ohms, of the above-mentioned voltmeter is
A. 500 B. 5,000
C. 250,000
D. 500,000

 

[junkhound]

Obsolete test question, who still uses a meter that is rated ohms/volt ?

 

[Dennis Alwon]

Obsolete test question, who still uses a meter that is rated ohms/volt ?

Alot of questions on exams are obsolete but I think it is more for the understanding of it. For instance, a question that states you 5 current carrying conductor's of #10 thw...... Nobody uses tw---but it is there for a purpose.