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Chapter 25: Problem 14

Why do light bulbs typically burn out just as they are turned on rather than while they are lit?

Short Answer

Expert verified
Answer: Light bulbs typically burn out just as they are turned on due to the combination of increased electrical resistance, rapid thermal expansion, and the stress on the weakened or brittle points of the filament at the turn-on stage.

Step by step solution

01

Understand the basic structure of a light bulb

A light bulb consists of a thin filament, often made of tungsten, enclosed in a glass bulb filled with inert gas. When an electric current passes through the filament, it heats up and emits light as a result.
02

Understand electrical resistance in a filament

As the filament heats up due to the electrical current passing through it, its resistance increases. This is due to the increase in the temperature resulting in an increased agitation of the atoms and electrons in the filament. The increased resistance means that more energy is converted into heat, making the filament even hotter, and ultimately resulting in the filament glowing and emitting light.
03

Understand thermal expansion

When the filament heats up, it undergoes thermal expansion. This means that the material expands as its temperature increases. When the material cools down again, it contracts. This expansion and contraction can eventually lead to the material becoming weakened or brittle, particularly at the points where the filament is attached to its supports.
04

Understand turn-on moment for light bulbs

When a light bulb is turned on, there is a sudden surge of electrical current passing through the filament that rapidly increases its temperature. This results in a sharp increase in electrical resistance and a corresponding increase in temperature, causing rapid thermal expansion.
05

Identify the reason for light bulbs burning out at turn-on

The rapid thermal expansion that occurs at the turn-on moment causes stress on the already weakened or brittle points of the filament. This additional stress can cause the filament to break, consequently resulting in the light bulb burning out. Since this process is more likely to occur when the filament is rapidly heated during the turn-on stage, light bulbs typically burn out just as they are turned on rather than while they are lit. In conclusion, the reason why light bulbs typically burn out just as they are turned on, rather than while they are lit, is due to the combination of increased electrical resistance, rapid thermal expansion, and the stress on the weakened or brittle points of the filament at the turn-on stage.

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Most popular questions from this chapter

A potential difference of \(V=0.500 \mathrm{~V}\) is applied across a block of silicon with resistivity \(8.70 \cdot 10^{-4} \Omega \mathrm{m}\). As indicated in the figure, the dimensions of the silicon block are width \(a=2.00 \mathrm{~mm}\) and length \(L=15.0 \mathrm{~cm} .\) The resistance of the silicon block is \(50.0 \Omega\), and the density of charge carriers is \(1.23 \cdot 10^{23} \mathrm{~m}^{-3}\) Assume that the current density in the block is uniform and that current flows in silicon according to Ohm's Law. The total length of 0.500 -mm-diameter copper wire in the circuit is \(75.0 \mathrm{~cm},\) and the resistivity of copper is \(1.69 \cdot 10^{-8} \Omega \mathrm{m}\) a) What is the resistance, \(R_{w}\) of the copper wire? b) What are the direction and the magnitude of the electric current, \(i\), in the block? c) What is the thickness, \(b\), of the block? d) On average, how long does it take an electron to pass from one end of the block to the other? \(?\) e) How much power, \(P\), is dissipated by the block? f) In what form of energy does this dissipated power appear?

A light bulb is connected to a source of emf. There is a \(6.20 \mathrm{~V}\) drop across the light bulb, and a current of 4.1 A flowing through the light bulb. a) What is the resistance of the light bulb? b) A second light bulb, identical to the first, is connected in series with the first bulb. The potential drop across the bulbs is now \(6.29 \mathrm{~V},\) and the current through the bulbs is \(2.9 \mathrm{~A}\). Calculate the resistance of each light bulb. c) Why are your answers to parts (a) and (b) not the same?

Which of the following wires has the largest current flowing through it? a) a 1 -m-long copper wire of diameter \(1 \mathrm{~mm}\) connected to a \(10-V\) battery b) a \(0.5-\mathrm{m}\) -long copper wire of diameter \(0.5 \mathrm{~mm}\) connected to a 5 -V battery c) a 2 -m-long copper wire of diameter \(2 \mathrm{~mm}\) connected to a \(20-V\) battery d) a \(1-\mathrm{m}\) -long copper wire of diameter \(0.5 \mathrm{~mm}\) connected to a 5 -V battery e) All of the wires have the same current flowing through them.

A water heater consisting of a metal coil that is connected across the terminals of a 15 -V power supply is able to heat \(250 \mathrm{~mL}\) of water from room temperature to boiling point in \(45 \mathrm{~s}\). What is the resistance of the coil?

The Stanford Linear Accelerator accelerated a beam consisting of \(2.0 \cdot 10^{14}\) electrons per second through a potential difference of \(2.0 \cdot 10^{10} \mathrm{~V}\) a) Calculate the current in the beam. b) Calculate the power of the beam. c) Calculate the effective ohmic resistance of the accelerator.
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