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Chapter 19: Q27Q (page 796)

Should an ammeter have a low or high resistance? Why? Should a voltmeter have a low or high resistance? Why?

Short Answer

Expert verified

An ammeter should have low resistance since it is connected in series. A voltmeter should have high resistance since it is connected in parallel.

Step by step solution

01

Given data

An ammeter and voltmeter are provided.

02

Current and resistance

Current through a circuit path is inversely proportional to the total resistance in that path.

03

Determination of resistances of ammeter and voltmeter

An ammeter is connected in series in a circuit. Hence it must have low resistance so as not to modify the total resistance of the circuit much. If it does, then it will modify the current which it has to measure.

A voltmeter is connected in parallel to the circuit. It provides an alternate path for the current to flow. So it must have very high resistance so that current doesn't flow through that path keeping the current and voltage in the original circuit unchanged.

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Most popular questions from this chapter

The capacitor in Figure 19.67 is initially uncharged, then the circuit is connected. Which graph in Figure 19.66 best describes the absolute value of the charge on the left plate as a function of time?

The capacitor in Figure 19.67 is initially uncharged, then the circuit is connected. Which graph in Figure 19.66 best describes the current through the bulb as a function of time?

A long Iron slab of width w and height h emerges from a furnace, as shown in Figure 19.79. Because the end of the slab near the furnace is hot and the other end Is cold, the electron mobility increases significantly with the distance x. The electron mobility is u=u0+kxwhere u0is the mobility of the iron at the hot end of the slab. There are n iron atoms per cubic meter, and each atom contributes one electron to the sea of the mobile electron (we can neglect the small thermal expansion of the iron). A steady state conventional current runs through the slab from the hot end towards cold end, and an ammeter (not shown) measures the current to have a magnitude I in amperes. A voltmeter is connected to two locations a distance d apart, as shown. (a) Show the electric field inside the slab at two locations marked with ×. Pay attention to the relative magnitudes of the two vectors that you draw. (b) Explain why the magnitude of the electric field is different at these two locations. (c) At a distance x from the left voltmeter connection, what is the magnitude of the electric field in terms x and the given quantities w,h,d,u0,k,l, and n ( and fundamental constants)? (d) What is the sign of potential difference displayed on the voltmeter? Explain briefly. (e) In terms of the given quantitiesw,h,d,u0,k,l, and n and ( and fundamental constants), what is the magnitude of the voltmeter reading? Check your work. (f) What is the resistance of this length of the iron slab?

Which of the following statements about the discharging of a capacitor through a light bulb are correct? Choose all that are true. (1) The fringe field of the capacitor decreases as the charge on the capacitor plates decreases. (2) Electrons flow across the gap between the plates of the capacitor, thus reducing the charge on the capacitor. (3) The electric field at a location inside the wire is due to charge on the surface of the wires and charge on the plates of the capacitor. (4) Electrons in the wires flow away from the negative plate toward the positive plate, reducing the charge on the plates.

A circuit consists of two batteries (with negligible resistance), six ohmic resistors and connecting wires that have negligible resistance. The resistance R1is 10Ω, R2 is 20Ω, R3 is 30Ω, R4is 12Ω, R5is 15Ω and R6 is 20Ω. Unknown currents I1,I2 ,I3 ,I4 , I5 and I6 have their directions marked on the circuit diagram in figure 19.87.

(a) Write down a set of equations that could be solved for the six unknown currents. Make sure you can explain how to you got these equations. (b) When a correct set of equations is solved the currents are as follows (to the nearest miiampeares) I1=0.4394A, I2=0.3312A, I3=0.0065A, I4=0.1082A, I5=0.3247Aand I6=0.4329A. Check your equations by substituting in these numbers. (c) Suppose that you connect the negative lead of a voltmeter to location C. What does the voltmeter read, including both magnitude and sign? (d) What does the power output of the 5 V battery? (e) Resistor is made of a very thin metal wire that is 3 mm long, with a diameter of 0.1 mm. What is the electric field inside the metal resistor.
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