l>Chapter 16 Concepts

chapter 18

Conceptual Questions: 4, 6, 9, 10, 13, 17, 21, 22, 23

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4. Jeff requirements a 100 Ohm resistor for a circuit, yet he only has actually a box of 300 Ohm resistors. What have the right to he do?

Jeff has actually a few options. First, he can go to the resistor store and also buy a various box, this time the 100 Ohm resistors, favor he should have the first time. But this isn\"t really where we were going through this question.

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What Jeff is supposed to carry out is to decrease the the full resistance. If he connects the resistors in series, they will certainly only rise the full resistance. However, if the connects lock in parallel with one another, climate they decrease the full resistance. 3 300 Ohm resistors in parallel will integrate to have a full of 100 Ohms the resistance, since 1/100 = 1/300 + 1/300 + 1/300. (Try that out for yourself.)

6. Compare the resistance of perfect ammeter through that of suitable voltmeter. Which has actually the larger resistance? Why?

An ammeter requirements to measure present without an altering the quantity of current that would usually be coming through a certain brand of a circuit. As a result, it needs to have an extremely low resistance. ~ above the various other hand, a voltmeter actions the voltage difference in between two different points (say, on various sides the a resistor), yet it should not readjust the amount of present going through the facet between those two points. So, it need to have very high resistance so the it doesn\"t \"draw\" existing through it. Inquiry 10 (below) offers more details top top this, and really should be answered in ~ the same time as this question, therefore let\"s skip to that one:

10. Why room ammeters linked in series with a circuit elementy in i beg your pardon the current is to be measured and also voltmeters connected in parallel across the element for which the potential difference is to be measured?

Ammeters are measuring current, for this reason they need to gain \"in\" the circuit and actually intercept and also count all the charges going through. You break the branch that the circuit you\"re measuring existing in, and then insert this meter, reconnecting the circuit through it \"seeing\" every these fees going with it. (It must have very very short resistance in this case, so the it doesn\"t adjust the conditions of the circuit and readjust the current flow.)

Voltmeters have to compare two different points and also their voltages. Through virtue of to compare the two points, you have actually to connect to those 2 at the exact same time, which needs a parallel connection. (The voltmeter need to have really high resistance so that it doesn\"t permit current to circulation through it and also thus adjust the currents in the rest of the circuit.)

What would occur if you hooked an ammeter increase in a configuration that was supposed for a voltmeter (i.e., in parallel)? That\"s a really an excellent exam question.

9. Why are electric stoves and clothes dryers gave with 240 V, yet lights, radios, and clocks are provided with 120 V?

Since strength (rate of energy) is the product of I and also V, you can get increased energy from this stoves and also dryers through simply raising the existing (by diminish the resistance of the facets within them). However, it isn\"t constantly a great idea to simply keep enhancing current, since this is physically demanding: much more charges moving through a wire way you need to have actually thicker cable with much less resistance, otherwise the wire might heat up too much and melt the insulation. So, the other method to boost the strength without raising the present too lot is to boost the voltage. This isn\"t crucial for most electric devices, but a great fit because that high power things.

13. Part batteries have the right to be \"recharged.\" does that mean that the battery has a supply of fee that is depleted together the battery is used? If \"recharging\" does not literally median to put charge earlier into the battery, what does the mean?

We don\"t produce nor destroy charge. And, the battery is never anything but neutrally charged. That moves fee around, but always with the same current going in one finish of the battery together what comes the end the the contrary end.

What is being excellent to the battery is to rise its potential energy as it\"s gift \"recharged.\" In batteries, this means there\"s some type of chemical adjust taking place, and also the energy stored in this is harvested later on as electrical energy.

17. An elecrician working on \"live\" circuits attract insulated shoes and keeps one hand behind his or her back. Why?

Insulated pair of shoes keeps the electrician isolated indigenous the ground, hope making higher resistance in a circuit the would affix him to ground. This higher resistance would result in a short (hopefully near-zero) current. The same human being keeps one hand behind his or her earlier just to show off. No, actually, the second hand would be a an excellent way to affix a complete circuit going best through the heart, and also keeping that behind your ago assures you the you don\"t do this connection. (Later in the semester I\"ll create a circuit through a pickle, for reasons you\"ll understand then, and also you\"ll watch a comparable technique. Hopefully.)

21. A. If the resistance R1 decreases, what happens to the voltage drop throughout R3? The switch S is tho open, together in the figure.

The existing will be larger in R3, boosting the voltage drop.

21. B. If the resistance R1 decreases, what happens ot the voltage drop across R2? The switch S is tho open, together in the figure.

It decreases, result from more current going v R1 (and R2 needs to share through R1).

21. C. In the circuits shown, if the switch S is closed, what happens to the current through R1?

It increases. In this case, no existing will go v R3 -- us say the it has been \"shorted out.\" This means there\"s less full resistance in the circuit, so an ext current to share v R1 and R2.

22. Four identical lightbulbs are put in two various circuits with the same batteries. Bulbs A and also B are linked in collection with the battery. Bulbs C and also D are connected in parallel throughout the battery.

a. Rank the brightness of the bulbs.

C and D will be same bright and brighter than A and also B; A and B are equally bright.

b. What wake up to the brightness of pear B if pear A is changed by a wire?

B rises in brightness.

c. What happens ot the brightness of bulb C if bulb D is gotten rid of from the circuit?

Its brightness stays the same.

23. Three the same lightbulbs are linked in a circuit as displayed in the diagram.

a. What happens to the brightness that the remaining bulbs if bulb A is gotten rid of from the circuuit and also replaced through a wire?

Bulbs B and also C get brighter.

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b. What wake up to the brightness of the reamining bulbs if bulb B is eliminated from the circuit?

Bulb A it s okay dimmer and also bulb C it s okay brighter. Through all 3 resistances in the circuit, the currents room IA = 2V/(3R), IB = IC = V/(3R). When B is removed, the existing in both A and also C is V/(2R). (Did you gain all that?)

c. What wake up to the brightness of the reamining bulbs if bulb B is changed by a wire?

Bulb A it s okay brighter, bulb C stop glowing entirely. (Bulb C has been shorted out by a wire v zero resistance, for this reason none of the present goes come C.)