Physics, 29.06.2019 19:00 josephvcarter

Which statement is true about ac? a). the electrons move back and forth b). the +/- polarity is constant c). it is most common in portable devices d). it can produce only low voltages

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Answer from: Nprz84

In a wire carrying Alternating Current, the electrons move "back and forth", first toward one end of the wire, then toward the other end of the wire. (A)

The + / - polarity of AC is constantly reversing. (B)

AC is most commonly used to power devices that plug into a wall outlet, and very very very seldom to power portable devices. (C)

AC is used at voltages anywhere between several hundred-thousand volts for long-distance interstate power transmission, to 3 or 4 volts coming out of a "wall wart" AC adapter in the house. (D) . Voltage of an AC is easily shifted with a transformer, whereas transformers can't be used for DC.

Answer from: Quest

The answer is frictional force

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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Which statement is true about ac? a). the electrons move back and forth b). the +/- polarity is co...

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