- #1
kihr
- 102
- 0
Homework Statement
A voltmeter reads 8V at full scale deflection, and is graded according to its resistance per volt at full scale deflection as 5000 ohms / volt. How will you convert it into a voltmeter that reads 20V at full scale deflection? Will it still be graded as 5000 ohms / volt.? Will you prefer this voltmeter to one that is graded ats 2000 ohms /volt?
Homework Equations
Application of Ohm's Law
The Attempt at a Solution
Let R = voltmeter resistance
I = current through voltmeter for full scale deflection
If the voltmeter has to read 20V at full scale deflection, we need an additional resistance r in series with it. Thus
8/R = 20/R+r
R = 5000 *8 (since the voltmeter is graded as 5000 ohms/V for full scale deflection
of 8V)
1/5000 = 20/40000 +r
r= 60000 ohms
The above has been calculated using the voltmeter grading as 5000 ohms /V.
I need some clues to proceed further with the next part of the question as I am not sure as to whether my way of looking at the voltmeter grading is correct or not.