What is the efficiency of a device that takes 400J of heat and does 120J of work while giving off 280 J of heat

30%

Explanation:

Efficiency = useful work / heat absorbed x 100

= 120/400 x 100

= 0.3 x 100

= 30%

b mirrors submit a iisner? e. for which optical devices does d sometimes have a positive value? o a a and b o b. a and c o c. b and d 0 d. b and cb

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.