Homework Help: Physics EM

Posted by Spencer on Monday, March 10, 2008 at 7:50pm.

A battery with EMF 90.0 V has internal resistance R_b = 8.68 Omega.
What is the reading V_v of a voltmeter having total resistance R_v = 485 \Omega when it is placed across the terminals of the battery?
Express your answer with three significant figures.
V_v =88.4V
This is the value I found is correct. I dont see how to solve this next question.

What is the maximum value that the ratio R_b/R_v may have if the percent error in the reading of the EMF of a battery is not to exceed 3.00 %?

Physics EM - Steve, Wednesday, October 22, 2008 at 1:27am
Give up - this question is impossible.
Physics EM - Steve, Wednesday, October 22, 2008 at 1:27am
roflcopter
Physics EM - JB, Tuesday, October 20, 2009 at 10:38pm
Physics2212 students... lets all protest against mastering physics.
Physics EM - Alina, Sunday, February 5, 2012 at 11:28pm
Consider the fractional error as
a = (V-V_v)/V

where a is equal to the 0.03 (because in this question the percent error is 3.00%)

You should know from Kirchhoff's rule that the Electric potential difference is

V=I(R_b+R_v)

You also found out that Elec. Poten. diff. with only the voltmeter as resistance is

V_v =IR_v

You plug in the Voltage equations to the first equation for the error and play a little with algebra you get the ratio as

R_b/R_v = (1/(1-a))-1

Got me the right answer. ;)

Answer this Question

Related Questions

repost physics E&M please - A battery with EMF 90.0 V has internal ...
Physics - The battery in the circuit diagram has an EMF of 12V and an unknown ...
Physics - The battery in the circuit diagram has an EMF of 12V and an unknown ...
Physics - A voltmeter of internal resistance of 5000 Ω is connected ...
Phyics - A resistor has a resistance R, and a battery has an internal resistance...
physics - The voltage across the terminals of a 8.90 V battery is 8.00 V when ...
Physics - Batteries are not perfect. Instead they have an "internal ...
College Physics - When switch S is open, the voltmeter V of the battery reads 3....
physics - Two bulbs are connected in parallel across a source of emf EMF = 10.0V...
PHYSICS - Two bulbs are connected in parallel across a source of emf EMF = 10.0V...

For Further Reading

First Name:
School Subject:
Answer: