4. (Note that script E in the figure stands for emf.). Since digital meters require less current than analog meters, they alter the circuit less than analog meters. (a) What current flows? Current sensitivity is the current that gives a full-scale deflection of the galvanometer’s needle, the maximum current that the instrument can measure. There are practical limits to galvanometer sensitivity, but it is possible to get analog meters that make measurements accurate to a few percent. Include a circuit diagram with your solution. (See Figure 7(a).) 12. 13. 1. Suppose you are using a multimeter (one designed to measure a range of voltages, currents, and resistances) to measure current in a circuit and you inadvertently leave it in a voltmeter mode. These IR drops are IR = IGr so that [latex]IR=\frac{{I}_{\text{G}}}{I}=\frac{R}{r}\\[/latex]. An ammeter is placed in series to get the full current flowing through a branch and must have a small resistance to limit its effect on the circuit. 11. In a circuit an ammeter and voltmeter is always connected in_____ and _____ respectively. A certain ammeter has a resistance of 5.00 × 10−5Ω on its 3.00-A scale and contains a 10.0-Ω galvanometer. (b) What is the resistance of the combination? Figure 4 shows how a galvanometer can be used as a voltmeter by connecting it in series with a large resistance, R. The value of the resistance R is determined by the maximum voltage to be measured. (a) A voltmeter having a resistance much larger than the device (RVoltmeter>>R) with which it is in parallel produces a parallel resistance essentially the same as the device and does not appreciably affect the circuit being measured. That choice involves switching an appropriate resistance into series with the galvanometer. ), Analog meters have a needle that swivels to point at numbers on a scale, as opposed to digital meters, which have numerical readouts similar to a hand-held calculator. A parallel connection is used because objects in parallel experience the same potential difference. The two crucial characteristics of a given galvanometer are its resistance and current sensitivity. Find the resistance that must be placed in series with a 25.0-Ω galvanometer having a 50.0-μA sensitivity (the same as the one discussed in the text) to allow it to be used as a voltmeter with a 3000-V full-scale reading. (A large resistance in parallel with a small one has a combined resistance essentially equal to the small one.) 5. You may need to download version 2.0 now from the Chrome Web Store. (b) Find the terminal voltage. 2. Figure 1. Unreasonable Results Suppose you have a40.0-Ω galvanometer with a 25.0-μA sensitivity. The circuit is essentially unaltered compared with when the ammeter is absent. 15. A 1.00-MΩ voltmeter is placed in parallel with a 75.0-kΩ resistor in a circuit. (e) Are the changes found in parts (c) and (d) significant? (c) If the voltage across the combination is kept the same as it was across the 75.0-kΩ resistor alone, what is the percent increase in current? Voltmeters measure voltage, and ammeters measure current. (c) To see how close the measured terminal voltage is to the emf, calculate their ratio. Click to download the simulation. For macroscopic systems, such as the circuits discussed in this module, the alteration can usually be made negligibly small, but it cannot be eliminated entirely. What is the sensitivity of the galvanometer (that is, what current gives a full-scale deflection) inside a voltmeter that has a 25.0-kΩ resistance on its 100-V scale? Most of the current (I) flowing through the meter is shunted through R to protect the galvanometer. There is another measurement technique based on drawing no current at all and, hence, not altering the circuit at all. For an ideal ammeter… 15. Another way to prevent getting this page in the future is to use Privacy Pass. 9. 2. Standard voltmeters and ammeters alter the circuit being measured and are thus limited in accuracy. (See Figure 3, where the ammeter is represented by the symbol A. A 0.0200-Ω ammeter is placed in series with a 10.00-Ω resistor in a circuit.

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