It is not possible to get a perfect Machine in our practice, why?​

No machine is perfect because some part of the work done on a machine is always used up or wasted in overcoming the friction between the moving parts of the machine. If a machine is 80% of the work input to the machine is obtained as the useful work output.

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adding a(n) to an electric circuit would increase the magnetic field around a wire;

b. solenoid

a solenoid is a type of electromagnet whose purpose is to generate a controlled magnetic field.

if the purpose of the solenoid is instead to impede changes in the electric current, a solenoid can be more specifically classified as an inductor rather than an electromagnet.