erer (1) A battery has an emf of 9.0 V. After connecting a light bulb, you measure the terminal voltage of the battery between points a and b to be 8.81 V and the current in the light bulb to be 752 mA. What is the internal resistance of the battery? (2) What is the resistance of the light bulb? a

erer (1) A battery has an emf of 9.0 V. After connecting a light bulb, you measure the terminal voltage of the battery between points a and b to be 8.81 V and the current in the light bulb to be 752 mA. What is the internal resistance of the battery? (2) What is the resistance of the light bulb? a

University Physics Volume 2

18th Edition

ISBN:9781938168161

Author:OpenStax

Publisher:OpenStax

Chapter10: Direct-current Circuits

Section: Chapter Questions

Problem 22P: An automobile starter motor has an equivalent resistance of 0.0500 and is supplied by a 12.0-V...

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Digital medical thermometers determine temperature by measuring the resistance of a semiconductor device called a thermistor (which has a=0.06/C ) when it isat 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 37C (normal bodytemperature)?
A car battery with a 12-V emf and an internal resistance of 0.050 is being charged with a current of 60 A. Note that in this process the battery is being charged. (a) What is the potential difference across its terminals? (b) At what rate is thermal energy being dissipated in the battery? (c) At what rate is electric energy being converted to chemical energy? (d) What are the answers to (a) and (b) when the battery is used to supply 60 A to the starter motor?
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?
(a) A defibrillator sends a 6.00-A current through the chest of a patient by applying a 10,000-V potential as in the figure below. What is the resistance of the path? (b) The defibrillator paddles make contact with the patient through a conducting gel that greatly reduces the path resistance. Discuss the difficulties that would ensue if a larger voltage were used to produce the same current through the patient, but with the path having perhaps 50 times the resistance. (Hint: The current must be about the same, so a higher voltage would imply greater power. Use this equation for power: P=I2 RP = .)
A 1,00-?O voltmeter is placed in parallel with a 75.0kresistor in a circuit, (a) Draw a circuit diagram of the connection, (b) What is the resistance of the combination? If the voltage across the combination is kept the same as it was across the 75.0-kresistor alone, what is the percent increase in current? (d) If the current through the combination is kept the same as it was through the 75.0-kresistor alone, what is the percentage decrease in voltage? (e) Are the changes found in parts (c) and (d) significant? Discuss.
(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.)
For the purpose of measuring the electric resistance of shoes through the body of the wearer standing on a metal ground plate, the American National Standards Institute (ANSI) specifies the circuit shown in Figure P27.14. The potential difference V across the 1.00-M resistor is measured with an ideal voltmeter. (a) Show that the resistance of the footwear is Rshoes=50.0VVV (b) In a medical test, a current through the human body should not exceed 150 A. Can the current delivered by the ANSI-specified circuit exceed 150 A? To decide, consider a person standing barefoot on the ground plate. Figure P27.14
Ralph has three resistors, R1, R2, and R3, connected in series. When connected to an ideal emf source E1, current I1 flows through the resistors. a. If the resistors are instead connected to a second source with E2=2E1, what is the new current through the resistors in terms of the first current? b. Show that, if each resistance is doubled and the resistors are connected in series to the second emf source, the current through the resistors is equal to I1.
The circuit in Figure P27.34a consists of three resistors and one battery with no internal resistance. (a) Find the current in the 5.00- resistor. (b) Find the power delivered to the 5.00- resistor. (c) In each of the circuits in Figures P27.34b, P27.34c, and P27.34d, an additional 15.0-V battery has been inserted into the circuit. Which diagram or diagrams represent a circuit that requires the use of Kirchhoffs rules to find the currents? Explain why. (d) In which of these three new circuits is the smallest amount of power delivered to the 10.0- resistor? (You need not calculate the power in each circuit if you explain your answer.) Figure P27.34
A car battery with a 12-V emf and an internal resistance of 0.050 is being charged with a current of 60 A. Note that in this process, the battery is being charged. (a)What is the potential difference across its terminals? (b)At what rate is thermal energy being dissipated in the battery? (c) At what rate is electric energy being converted into chemical energy?
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,
Consider the circuit shown in Figure P28.21 on page 860. (a) Find the voltage across the 3.00-0 resistor, (b) Find the current in the 3.00-12 resistor.