Aresistor dissipates 0.25 w when current of 20 ma passes through it. part a how much current would be needed for the resistor to dissipate 0.50 w? how much current would be needed for the resistor to dissipate 0.50 ? 56 ma 28 ma 40 ma 80 ma

Power dissipated by a resistor = (current)² x (resistance).

0.25 W = (0.02 A)² x (resistance)

This resistor = (0.25 W) / (0.02 A)²

This resistor = 625 ohms

If we want it to dissipate 0.5 W, then

0.5 W = (current)² x (625 ohms)

Current = √(0.5/625)

Current = √(0.0008)

Current = 28.28 mA

A slightly easier way:

Since the power is = I²R, it grows in proportion to (current)² .

We want to double the power dissipated, so we only need to increase the current by the factor of √2 .

(20 mA) x (√2) = 28.28 mA

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 -

                                              ⇒      

here   k is the proportionality constant whose value is 1.

                                                            [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.