5. During the Christmas season, Sel Erbate uses the equivalent of 45 strings of 100 mini-bulbs to light the inside and outside of his home. Each 100-bulb string of lights is rated at 40 Watts. The average daily usage of the strings is 7 hours. The lights are used for approximately 40 days during the holiday season. a. Determine the resistance of each string of lights. Each is powered by 110-volt outlet. b. Determine the energy consumed (in kWh) by all of the lights over the course of 40 days. c. If Sel pays 12 cents/kWh for electrical energy, then what is the total cost of Christmas lighting for a single season?

5. During the Christmas season, Sel Erbate uses the equivalent of 45 strings of 100 mini-bulbs to light the inside and outside of his home. Each 100-bulb string of lights is rated at 40 Watts. The average daily usage of the strings is 7 hours. The lights are used for approximately 40 days during the holiday season. a. Determine the resistance of each string of lights. Each is powered by 110-volt outlet. b. Determine the energy consumed (in kWh) by all of the lights over the course of 40 days. c. If Sel pays 12 cents/kWh for electrical energy, then what is the total cost of Christmas lighting for a single season?

University Physics Volume 2

18th Edition

ISBN:9781938168161

Author:OpenStax

Publisher:OpenStax

Chapter9: Current And Resistance

Section: Chapter Questions

Problem 93CP: A physics student uses a 115.00-V immersion heater to heat 400.00 grams (almost two cups) of water...

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Integrated Concepts (a) An immersion heater utilizing 120 V can raise the temperature of a 1.00 102 -g aluminum cup containing 350 g of water from 20.0°C to 95.0°C in 2.00 min. Find its resistance, assuming it is constant during the process. (b) A lower resistance would shorten the heating time. Discuss the practical limits to speeding the heating by lowering the resistance.
A physics student uses a 115.00-V immersion heater to heat 400.00 grams (almost two cups) of water for herbal tea. During the two minutes it takes the water to heat, the physics student becomes bored and decides to figure our the resistance of the heater. The student starts with the assumption that the water is initially at the temperature of the room Ti=25.00C and reaches Tf=100.00C . The specific heat of the water is c=4180JkgK What is the resistance of the heater?
The human body can exhibit a wide range of resistances to current depending on the path of the current, contact area, and sweatiness of the skin. Suppose the resistance across the chest from the left hand to the right hand is 1.0 106 . (a) How much voltage is required to cause possible heart fibrillation in a man, which corresponds to 500 mA of direct current? (b) Why should rubber-soled shoes and rubber gloves be worn when working around electricity?
A 120-V circuit in a house is equipped with a 20-A fuse that will b1ow if the current exceeds 20 A. What is the smallest resistance that can be plugged into the circuit without causing the fuse to blow?
Find the current through a person and identify the likely effect on her if she touches a 120-V ac source: (a) if she is standing on a rubber mat and offers a total resistance of 300 k (b) if she is standing barefoot on wet grass and has a resistance of only 4000 k .
. All of the electrical outlets in a room are connected in a single parallel circuit (Figure 7.38). The circuit is equipped with a 20-A fuse, and the voltage is 120 V. (a) What is the maximum total power that can be supplied by the outlets without blowing the fuse? (b) How many 1,200-W appliances can be plugged into the sockets without blowing the fuse?
The hot resistance of a flashlight bulb is 2.30 , and it is run by a 1.58-V alkaline cell having a 0.100-O internal resistance. (a) What current flows? (b) Calculate the power supplied to the bulb using I2Rbulh? (c). power the same as calculated using V2Rbulb?
What would be the maximum cost of a CFL such that the total cost (investment plus operating) would be the same for both CFL and incandescent 60-W bulbs? Assume the cost of the incandescent bulb is 25 cents and that electricity costs 10 cents/kWh, Calculate the cost for 1000 hours, as in the cost effectiveness of CFL example.
The label or a portable radio recommends the use of rechargeable nickel-cadmium cells (nicads), although they have a 1.25-V emf while alkaline cells have a 1.58-V emf. The radio has a 3.20- resistance, (a) Draw a circuit diagram ot the radio and its batteries. Now, calculate the power delivered to the radio, (b) When using Nicad cells each having an internal resistance of 0.0400O. (c) When using alkaline cells each having an internal resistance of 0.200 . (d) Does this difference seem significant, considering that the radio s effective resistance is lowered when its volume is turned 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 the current 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.)
A 14-gauge copper wire has a diameter of 1.628 mm. What magnitude current flows when the drift velocity is 1.00 mm/s? (See above example on Example 20.3 for useful information.)
Some makes of older cars have 6.00-V electrical systems. (a) What is the hot resistance of a 30.0-W headlight in such a car? (b) What current flows through it?