# electrical measuring instruments

Discussion in 'Homework Help' started by Raymond kunda, Sep 3, 2013.

1. ### Raymond kunda Thread Starter New Member

Aug 26, 2013
7
0
Guys help needed
A moving-iron instrument gives full scale deflection with 200v.it has a coil of 20000 turns and resistance of 3000Ω if the instrument is used as an ammeter to give a full scale deflection of 10.calculate the required number of turns. please guys

2. ### Ramussons Well-Known Member

May 3, 2013
754
133
10 what? milli amp or amp?

Hint: the deflection is dependent on the current flow and the number of turns.

Ramesh

3. ### WBahn Moderator

Mar 31, 2012
23,558
7,209
The question seems a bit contradictory. You have an instrument that has 20,000 turns. You are told to use that instrument to make an ammeter. Then you are asked for the required number of turns. Well, if you change the number of turns you have a different instrument. Are you supposed to assume that you are wiring up a new instrument using the same forms and just changing the number of turns?

4. ### JoeJester AAC Fanatic!

Apr 26, 2005
3,972
1,762
Something is amiss. You tell us the full scale voltage is 200v. You state the meter is 20,000 turns of wire and 3000 ohms of resistance. Is the resistance a "resistor" in series with the d'Arsonval meter?

5. ### #12 Expert

Nov 30, 2010
18,076
9,676
Maybe you need help because the question was not valid?

JoeJester likes this.
6. ### JoeJester AAC Fanatic!

Apr 26, 2005
3,972
1,762
True. The OP may have even typed the question wrong.

I'd like to see the section of the course material that the professor/instructor used when they discussed this material.

Actually, it can be worked out, but, the sensitivity of the meter would probably replicate something Kirchoff or Ohm actually used in their earliest laboratory.

Last edited: Sep 4, 2013
7. ### Raymond kunda Thread Starter New Member

Aug 26, 2013
7
0
sorry the 10 is current............but the number of turns is the the way it is and the resistance 3000 ohms

the question is from a past examination paper

8. ### Raymond kunda Thread Starter New Member

Aug 26, 2013
7
0
i tried to solve it in this manner

I=V/R
I=200/3000
I=0.067A

Then i multiplied the current and the turns to get the amp-turns =1333.333

then i made T the subject of the formula and i got 133.33AT
WHAT RE GETTING?

9. ### WBahn Moderator

Mar 31, 2012
23,558
7,209
10 is a number, it is not a current.

10A is a current, 10mA is a current, 10μA is a current, 10kA is a current.

10 is not a current.

What is the current?

10. ### JoeJester AAC Fanatic!

Apr 26, 2005
3,972
1,762
Last edited: Sep 4, 2013