1. Jenny bought a resistor made up of unknown material with color bands (red-green-black- brown-silver) to be used in her school project. She used a multimeter to measure the resistance of the resistor and she found out that the resulting value is exactly the upper limit of the value of the resistance. The length of the resistor is 5 cm and the radius of the cross-sectional area is 1.7011 mm. (Assume that the shape of the resistor is perfectly cylindrical.) A. Find the resistance value (upper limit). B. Find the resistivity of the resistor| C. What type of material is the resistor made of?

1. Jenny bought a resistor made up of unknown material with color bands (red-green-black- brown-silver) to be used in her school project. She used a multimeter to measure the resistance of the resistor and she found out that the resulting value is exactly the upper limit of the value of the resistance. The length of the resistor is 5 cm and the radius of the cross-sectional area is 1.7011 mm. (Assume that the shape of the resistor is perfectly cylindrical.) A. Find the resistance value (upper limit). B. Find the resistivity of the resistor| C. What type of material is the resistor made of?

Physics for Scientists and Engineers with Modern Physics

10th Edition

ISBN:9781337553292

Author:Raymond A. Serway, John W. Jewett

Publisher:Raymond A. Serway, John W. Jewett

Chapter27: Direct-current Circuits

Section: Chapter Questions

Problem 7P: You are working at an electronics fabrication shop. Your current project is on the team producing...

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Review. When a straight wire is warmed, its resistance is given by R = R0,[1 + a(T T0)] according to Equation 27.20, where a is the temperature coefficient of resistivity. This expression needs to be modified if we include the change in dimensions of the wire due to thermal expansion. For a copper wire of radius 0.100 0 mm and length 2.000 m, find its resistance at 100.0C, including the effects of both thermal expansion and temperature variation of resistivity. Assume the coefficients are known to four significant figures.
Show that the power dissipated by the load resistor is maximum when the resistance of the load resistor is equal to the internal resistance of the battery.
Explain why R=R0(1 + a?T) for the temperature variation of the resistance R of an object is not as accurate as P=P0(1 + a?T) which gives the temperature variation of resistivity P.
A child’s electronic toy is supplied by three 1.58-V alkaline cells having internal resistances of 0.0200 in series with a 1.53-V carbon-zinc dry cell having a 0.100- internal resistance. The load resistance is 10.0 . (a) Draw a circuit diagram of the toy and its batteries, (b) What current flows? (c) How much power is supplied to the load? (d) What is the internal resistance of the dry cell if it goes bad, resulting in only 0.500 W being supplied to the load?
When a straight wire is heated, its resistance changes according to the equation R = R0 [1 + (T T0)] (Eq. 17.7), where is the temperature coefficient of resistivity. (a) Show that a more precise result, which includes the length and area of a wire change when it is heated, is R=R0[1+(TT0)][1+(TT0)][1+2(TT0)] where is the coefficient of linear expansion. (See Topic 10.) (b) Compare the two results for a 2.00-m-long copper wire of radius 0.100 mm, starting at 20.0C and heated to 100.0C.
(a) Digital medical thermometers determine temperature by measuring the resistance of a semiconductor device called a thermistor (which has a= - 0.0600/°C ) when it is at the same temperature as the patient. What is a patient's temperature if the thermistor’s resistance at that temperature is 82.0% of its value at 37.0°C (normal body temperature)? (b) The negative value for a may not be maintained for very low temperatures. Discuss why and whether this is the case here. (Hint: Resistance can’t become negative.)
Why is the following situation impossible? A technician is testing a circuit that contains a resistance R. He realizes that a better design for the circuit would include a resistance 73R rather than R. He has three additional resistors, each with resistance R. By combining these additional resistors in a certain combination that is then placed in series with the original resistor, he achieves the desired resistance.
A child's electronic toy is supplied by three 1.58-V alkaline cells having internal resistances of 0.0200 inseries with a 1.53-V carbon-zinc dry cell having a 0.100- internal resistance. The load resistance is 10.0 . (a) Draw a circuit diagram of the toy and itsbatteries, (b) What current flows? (c) How much power is supplied to the load? (d) What is the internal resistance of the dry cell if it goes bad, resulting in only 0.500 W being supplied to the load?
The label on a battery-powered radio recommends the use of a rechargeable nickel-cadmium cell (nicads), although it has a 1.25-V emf, whereas an alkaline cell has a 1.58-V emf. The radio has a 3.20 resistance.(a) Draw a circuit diagram of the radio and its battery. Now, calculate the power delivered to the radio (b) when using a nicad cells, each having an internal resistance of 0.0400 , and (c) when using an alkaline cell, having an internal resistance of 0.200 . (d) Does this differenceseem significant, considering that the radio's effective resistance is lowered when its volume is aimed up?
An automobile starter motor has an equivalent resistance of 0.0500 and is supplied by a 12.0-V battery with a 0.0100- internal resistance, (a) What is thecurrent to the motor? (b) What voltage is applied to it? (c) What power is supplied to the motor? (d) Repeat these calculations for when the battery connections are corroded and add 0.0900 to the circuit. (Significant problems are caused by even small amounts of unwanted resistance in low-voltage, high-current applications.)
You are working at an electronics fabrication shop. Your current project is on the team producing resistors for the timer circuit that delays the closing of an elevator door. According to its design specification, the timer circuit is to have a resistance of 32.0 between two points A and B. As your resistors come off the assembly line, you find that they have a variation of 5.00% from this value. After a team meeting to evaluate this situation, the team decides that resistances in the range 32.0 0.5 are acceptable and do not need modification. For resistances outside this range, the director does not wish to discard the resistors, but rather to add extra resistors in series or parallel with the main resistor to bring the total equivalent resistance to the exact design value of 32.0 . You are put in charge of procuring the extra resistors. What range of resistances for these extra resistors do you need to cover the entire range of variation of 5.00%? All resistances can be measured to three significant figures.
A person with body resistance between his hands of 1.00 k accidentally grasps the terminals of a 20.0-kV power supply. (Do NOT do this!) (a) Draw a circuit diagram to represent the situation. (b) If the internal resistance of the power supply is 2000 , what is the current through his body? (c) What is the power dissipated in his body? (d) If the power supply is to be made safe by increasing its internal resistance, what should the internal resistance be for the maximum current in this situation to be 1.00 mA or less? (e) Will this modification compromise the effectiveness of the power supply for driving low-re si stance devices? Explain your reasoning,