Math question

[nickelec]

Stumped

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[jumper]

Here is a tutorial on the subject of meters and resistance.


https://www.allaboutcircuits.com/textbook/direct-current/chpt-8/voltmeter-design/

 

[Frank DuVal]

I get 147 ohms. Not one of the choices. maybe that's why he's stumped?:?

3 volts full scale and 3 ohm meter movement, means full scale is 1 (one) Amp!

To put one amp through the meter at 150 volts potential, one needs a 147 ohm series resistor.

I think a K has been left out of the question. Or at least two zeros.

 

[gar]

180124-1138 EST

Whoever wrote the question is totally screwed up.

If the meter was a 3 V DC meter with an internal resistance of 3 k-ohms, then it would be classified as a 1000 ohms per volt meter, or it uses a 1 mA meter movement, typical possibly before the mid 1940s. After the mid 1940s 20,000 ohms per V became typical (the Simpson 260).

Assuming 1000 ohms per volt, then total resistance has to be 150,000 ohms to make it a 150 V full scale meter. Thus, an external 147,000 ohm resistor is required.

A modern Simpson 260 has a 50 microampere movement or 20,000 ohms per volt, and has a total resistance of 250 * 20,000 = 5,000,000 ohms on the DC 250 V range. Note: the 260 in recent times is 5,000 ohms per volt on AC, and in the past was 1000 ohms per volt for AC.

.

 

[Besoeker]

180124-1138 EST

Whoever wrote the question is totally screwed up.

A 3 ῼ movement ???

 

[retirede]

A 3 ῼ movement ???

The ultimate "low impedance" meter!

 

[jumper]

The question is screwed up but my guess is that the author was trying to get at something like this from the link I posted above.

 

[steve66]

180124-1138 EST

Whoever wrote the question is totally screwed up.

If the meter was a 3 V DC meter with an internal resistance of 3 k-ohms, then it would be classified as a 1000 ohms per volt meter, or it uses a 1 mA meter movement, typical possibly before the mid 1940s. After the mid 1940s 20,000 ohms per V became typical (the Simpson 260).

Assuming 1000 ohms per volt, then total resistance has to be 150,000 ohms to make it a 150 V full scale meter. Thus, an external 147,000 ohm resistor is required.

A modern Simpson 260 has a 50 microampere movement or 20,000 ohms per volt, and has a total resistance of 250 * 20,000 = 5,000,000 ohms on the DC 250 V range. Note: the 260 in recent times is 5,000 ohms per volt on AC, and in the past was 1000 ohms per volt for AC.

.

Then it seems the question was supposed to include 300 ohms as the meter resistance, and then the answer would be b.