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Chapter 19: Q50P (page 799)

When a single thin-filament bulb is connected to a 1.5Vbattery, the current through the battery is about80mAIf you add another thin-filament bulb in parallel, the battery current of course increase to160mA. Is the battery ohmic? That is, is the current through the battery proportional to the potential difference across the battery?

Short Answer

Expert verified

No

Step by step solution

01

Given Data

VoltageV=1.5VCurrentI1=80mAI2=160mA

02

Concept

Generally, the current is proportional to the difference of electric potential. The current is inversely proportional to the resistance.

03

Find the battery is ohmic

  • The battery is not ohmic.
  • The current is not proportional to voltage.
  • If you double the current through a battery, the battery voltage hardly changes at all.
  • The battery voltage certainly does not double and will actually decrease slightly.
  • The battery voltage is not proportional to the current.

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Most popular questions from this chapter

Using thick connecting wires that are very good conductors, a Nichrome wire (“wire 1”) of length L1 and cross-sectional area A1 is connected in series with a battery and an ammeter (this is circuit 1). The reading on the ammeter is I1. Now the Nichrome wire is removed and replaced with a different wire (“wire 2”), which is 2.5 times as long and has 5.5 times the cross-sectional area of the original wire (this is circuit 2). In the following question, a subscript 1 refers to circuit 1, and a subscript 2 refers to circuit 2. It will be helpful to write out your solutions to the following questions algebraically before doing numerical calculations. (Hint: Think about what is the same in these two circuits.)(a) What is the value of I2/ I1, the ratio of the conventional currents in the two circuits? (b) What is the value of R2/ R1, the ratio of the resistances of the wires? (c) What is the value of E2/ E1, the ratio of the electric fields inside the wires in the steady states?

The deflection plates in an oscilloscope are 10cm by 2cm with a gap distance of 1mm. A 100V potential difference is suddenly applied to the initially uncharged plates through a 1000 Ωresistor in series with the deflection plates. How long does it take for the potential difference between the deflection plates to reach 95V?

In copper at room temperature, the mobility of mobile electrons is about 4.5×10-3(m/s)V/m,and there are about8×1028mobile electrons perm3Calculate the conductivityσand include the correct units. In actual practice, it is usually easier to measure the conductivityσand deduce the mobilityufrom this measurement.

The conductivity of tungsten at room temperature,1.8×107A/m2/V/m , is significantly smaller than that of copper. At the very high temperature of a glowing light-bulb filament (nearly 3000 kelvins), the conductivity of tungsten is 18 times smaller than it is at room temperature. The tungsten filament of a thick-filament bulb has a radius of about 0.015 mm. Calculate the electric field required to drive 0.20 A of current through the glowing bulb and show that it is very large compared to the field in the connecting copper wires.

A circuit consists of a battery, whose emf is K, and five Nichrome wires, three thick and two thin as shown in Figure 19.78. The thicknesses of the wires have been exaggerated in order to give you room to draw inside the wires. The internal resistance of the battery is negligible compared to the resistance of the wires. The voltmeter is not attached until part (e) of the problem. (a) Draw and label appropriately the electric field at the locations marked × inside the wires, paying attention to appropriate relative magnitudes of the vectors that you draw. (b) Show the approximate distribution of charges for this circuit. Make the important aspects of the charge distribution very clear in your drawing, supplementing your diagram if necessary with very brief written descriptions on the diagram. Make sure that parts (a) and (b) of this problem are consistent with each other. (c) Assume that you know the mobile-electron density n and the electron mobility u at room temperature for Nichrome. The lengths (L1,L2,L3)and diameters (d1,d2)of the wires are given on the diagram. Calculate accurately the number of electrons that leave the negative end of the battery every second. Assume that no part of the circuit gets very hot. Express your result in terms of the given quantities (K,L1,L2,L3,d1,d2,nandu). Explain your work and identify the principles you are using. (d) In the case that d2≪d1, what is the approximate number of electrons that leave the negative end of every second? (e) A voltmeter is attached to the circuit with its + lead connected to location B (halfway along the leftmost thick wire) and its - lead connected to location C (halfway along the leftmost thin wire). In the case that d2≪d1, what is the approximate voltage shown on the voltmeter, including sign? Express your result in terms of the given quantities(K,L1,L2,L3,d1,d2,nandu).
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