Physics, 07.04.2020 15:50 parmer6527p810bw

A small bulb is rated at 7.5 W when operated at 125 V. The tungsten filament has a temperature coefficient of resistivity α = 0.0045/°C. When the filament is hot and glowing, its temperature is seven times room temperature (20 °C). What is the resistance of the filament (in ohms) at room temperature? Group of answer choices 1911 1350 1280 5630 4530

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To solve this problem we will apply the concepts related to resistance as a function of temperature, product of the relationship between the squared voltage and the power. Mathematically this is,

$R = \frac{v^2}{P}$

Here,

R = Resistance (At function of temperature)

v = Voltage

P = Power

Then we have,

R at 140°C (7 times room temperature),

$R(140\°C) = \frac{125^2}{7.5}$

$R(140\°C) = 2083.33\Omega$

The relationship between normal temperature and increased temperature would then be given by,

$R(140\°C) = R(20\°C)(1 +\alpha (\Delta T))$

$R(140\°C) = R(20\°C)(1+(4.5*10^{-3})(140-20))$

$R(20\°C) = \frac{2083.33}{1.54}$

$R(20\°C) = 1352.81\Omega$

Therefore the correct value of the group of answer is 1350

Answer from: Quest

Hypothesis. why don’t you know this? i learned this stuff in like 5th grade

Answer from: Quest

force is based upon mass and acceleration.the statement is not always true.

it can be explained from newton's second law of motion.

as per newton's second law of motion the rate of change of momentum is directly proportional to the applied force and takes place along the direction of force.

mathematically it can be written as -

$f\alpha \frac{dp}{dt}$

⇒ $f= k \frac{dp}{dt}$

here k is the proportionality constant whose value is 1.

$f=\frac{dp}{dt}$

$f= \frac{d[mv]}{dt}$

$f= m\frac{dv}{dt} +v\frac{dm}{dt}$

$f=ma+v\frac{dm}{dt}$ [a is the acceleration=dv/dt]

hence we see that force not only depends on mass and acceleration but also on velocity and rate of change of mass. force f will depend on mass and acceleration only when mass is constant.

hence the statement that force is based upon mass and acceleration is false.

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