Advertisements
Advertisements
Question
The current in a conductor and the potential difference across its ends are measured by an ammeter and a voltmeter. The meters draw negligible currents. The ammeter is accurate but the voltmeter has a zero error (that is, it does not read zero when no potential difference is applied). Calculate the zero error if the readings for two different conditions are 1.75 A, 14.4 V and 2.75 A, 22.4 V.
Advertisements
Solution
Let the magnitude of zero error in the voltmeter reading be V.
We need to subtract the zero error from the readings obtained under the two given conditions to obtain the true value of potential difference.
Under both the conditions ,the resistance of the wire will not change.
\[\Rightarrow R_1 = R_2 \]
\[ \Rightarrow \frac{V_1}{I_1} = \frac{V_2}{I_2}\]
\[\frac{I_1 R}{I_2 R} = \frac{V_1}{V_2}\]
\[ \Rightarrow \frac{1 . 75}{2 . 75} = \frac{14 . 4 - V}{22 . 4 - V}\]
\[ \Rightarrow \frac{0 . 35}{0 . 55} = \frac{14 . 4 - V}{22 . 4 - V}\]
\[ \Rightarrow \frac{7}{11} = \frac{14 . 4 - V}{22 . 4 - V}\]
\[ \Rightarrow 7 \times \left( 22 . 4 - V \right) = 11\left( 14 . 4 - V \right)\]
\[ \Rightarrow 156 . 8 - 7V = 158 . 4 - 11V\]
\[ \Rightarrow \left( 7 - 11 \right)V = 156 . 8 - 158 . 4\]
\[ \Rightarrow - 4V = - 1 . 6\]
\[ \Rightarrow V = 0 . 4 V\]
Magnitude of zero error, V = 0.4 V, which can either be positive or negative. Positive or negative zero error just indicates that the needle of the voltmeter is to the right or left of the zero marked on the device if zero voltage is applied across the voltmeter.
APPEARS IN
RELATED QUESTIONS
In the following potentiometer circuit, AB is a uniform wire of length 1 m and resistance 10 Ω. Calculate the potential gradient along the wire and balance length AO (= l).
In a series LCR circuit, what is the phase difference between VL and VC where VL is the potential difference across the inductor and V c is the potential difference across the capacitor?
Why are Si and GaAs preferred materials for solar cells?
The emf of a cell is always greater than its terminal voltage. Why? Give reason.
Identify the correct options.
(a) An ammeter should have small resistance.
(b) An ammeter should have large resistance.
(c) A voltmeter should have small resistance.
(d) A voltmeter should have large resistance.
The potential difference between the terminals of a battery of emf 6.0 V and internal resistance 1 Ω drops to 5.8 V when connected across an external resistor. Find the resistance of the external resistor.
A voltmeter of resistance 400 Ω is used to measure the potential difference across the 100 Ω resistor in the circuit shown in the figure. (a) What will be the reading of the voltmeter? (b) What was the potential difference across 100 Ω before the voltmeter was connected?
A voltmeter consists of a 25 Ω coil connected in series with a 575 Ω resistor. The coil takes 10 mA for full-scale deflection. What maximum potential difference can be measured by this voltmeter?
If a constant potential difference is applied across a bulb, the current slightly decreases as time passes and then becomes constant. Explain.
A copper strip AB and an iron strip AC are joined at A. The junction A is maintained at 0°C and the free ends B and C are maintained at 100°C. There is a potential difference between _______________ .
(a) the two ends of the copper strip
(b) the copper end and the iron end at the junction
(c) the two ends of the iron strip
(d) the free ends B and C
A potential difference of 220 V is maintained across 12000 Ω rheostat. Then voltmeter V has a resistance of 6000 Ω and point C is at one fourth the distance from a to b. Then the reading of voltmeter is ______.
Two sources of equal e.m.f are connected to an external resistance R in series. The internal resistance of the two sources are R1 and R2 (R2 > R1) If the potential difference across the source having internal. resistance R2 is zero, then ______.
The terminal potential difference of a cell is greater than its e.m.f when it is ______
